diff --git a/Documentation/config/core.txt b/Documentation/config/core.txt
index e909b26001c9bb..66517d16c741fb 100644
--- a/Documentation/config/core.txt
+++ b/Documentation/config/core.txt
@@ -68,6 +68,14 @@ core.fsmonitor::
 	avoiding unnecessary processing of files that have not changed.
 	See the "fsmonitor-watchman" section of linkgit:githooks[5].
 
+core.virtualFilesystem::
+	If set, the value of this variable is used as a command which
+	will identify all files and directories that are present in
+	the working directory.  Git will only track and update files
+	listed in the virtual file system.  Using the virtual file system
+	will supersede the sparse-checkout settings which will be ignored.
+	See the "virtual file system" section of linkgit:githooks[6].
+
 core.trustctime::
 	If false, the ctime differences between the index and the
 	working tree are ignored; useful when the inode change time
@@ -600,6 +608,48 @@ core.multiPackIndex::
 	single index. See link:technical/multi-pack-index.html[the
 	multi-pack-index design document].
 
+core.gvfs::
+	Enable the features needed for GVFS.  This value can be set to true
+	to indicate all features should be turned on or the bit values listed
+	below can be used to turn on specific features.
++
+--
+	GVFS_SKIP_SHA_ON_INDEX::
+		Bit value 1
+		Disables the calculation of the sha when writing the index
+	GVFS_MISSING_OK::
+		Bit value 4
+		Normally git write-tree ensures that the objects referenced by the
+		directory exist in the object database. This option disables this check.
+	GVFS_NO_DELETE_OUTSIDE_SPARSECHECKOUT::
+		Bit value 8
+		When marking entries to remove from the index and the working
+		directory this option will take into account what the
+		skip-worktree bit was set to so that if the entry has the
+		skip-worktree bit set it will not be removed from the working
+		directory.  This will allow virtualized working directories to
+		detect the change to HEAD and use the new commit tree to show
+		the files that are in the working directory.
+	GVFS_FETCH_SKIP_REACHABILITY_AND_UPLOADPACK::
+		Bit value 16
+		While performing a fetch with a virtual file system we know
+		that there will be missing objects and we don't want to download
+		them just because of the reachability of the commits.  We also
+		don't want to download a pack file with commits, trees, and blobs
+		since these will be downloaded on demand.  This flag will skip the
+		checks on the reachability of objects during a fetch as well as
+		the upload pack so that extraneous objects don't get downloaded.
+	GVFS_BLOCK_FILTERS_AND_EOL_CONVERSIONS::
+		Bit value 64
+		With a virtual file system we only know the file size before any
+		CRLF or smudge/clean filters processing is done on the client.
+		To prevent file corruption due to truncation or expansion with
+		garbage at the end, these filters must not run when the file
+		is first accessed and brought down to the client. Git.exe can't
+		currently tell the first access vs subsequent accesses so this
+		flag just blocks them from occurring at all.
+--
+
 core.sparseCheckout::
 	Enable "sparse checkout" feature. See section "Sparse checkout" in
 	linkgit:git-read-tree[1] for more information.
diff --git a/Documentation/config/status.txt b/Documentation/config/status.txt
index ed72fa7daece09..1f20eb5551e4c0 100644
--- a/Documentation/config/status.txt
+++ b/Documentation/config/status.txt
@@ -12,6 +12,11 @@ status.branch::
 	Set to true to enable --branch by default in linkgit:git-status[1].
 	The option --no-branch takes precedence over this variable.
 
+status.aheadBehind::
+	EXPERIMENTAL, Set to true to enable --ahead-behind and false to
+	enable --no-ahead-behind by default in linkgit:git-status[1] for
+	non-porcelain status formats.  Defaults to true.
+
 status.displayCommentPrefix::
 	If set to true, linkgit:git-status[1] will insert a comment
 	prefix before each output line (starting with
@@ -70,3 +75,25 @@ status.submoduleSummary::
 	the --ignore-submodules=dirty command-line option or the 'git
 	submodule summary' command, which shows a similar output but does
 	not honor these settings.
+
+status.deserializePath::
+	EXPERIMENTAL, Pathname to a file containing cached status results
+	generated by `--serialize`.  This will be overridden by
+	`--deserialize=<path>` on the command line.  If the cache file is
+	invalid or stale, git will fall-back and compute status normally.
+
+status.deserializeWait::
+	EXPERIMENTAL, Specifies what `git status --deserialize` should do
+	if the serialization cache file is stale and whether it should
+	fall-back and compute status normally.  This will be overridden by
+	`--deserialize-wait=<value>` on the command line.
++
+--
+* `fail` - cause git to exit with an error when the status cache file
+is stale; this is intended for testing and debugging.
+* `block` - cause git to spin and periodically retry the cache file
+every 100 ms; this is intended to help coordinate with another git
+instance concurrently computing the cache file.
+* `no` - to immediately fall-back if cache file is stale.  This is the default.
+* `<timeout>` - time (in tenths of a second) to spin and retry.
+--
diff --git a/Documentation/fetch-options.txt b/Documentation/fetch-options.txt
index fa0a3151b3f7e9..3680082ae7ebc6 100644
--- a/Documentation/fetch-options.txt
+++ b/Documentation/fetch-options.txt
@@ -220,6 +220,19 @@ endif::git-pull[]
 	When multiple `--server-option=<option>` are given, they are all
 	sent to the other side in the order listed on the command line.
 
+--show-forced-updates::
+	By default, git checks if a branch is force-updated during
+	fetch. This can be disabled through fetch.showForcedUpdates, but
+	the --show-forced-updates option guarantees this check occurs.
+	See linkgit:git-config[1].
+
+--no-show-forced-updates::
+	By default, git checks if a branch is force-updated during
+	fetch. Pass --no-show-forced-updates or set fetch.showForcedUpdates
+	to false to skip this check for performance reasons. If used during
+	'git-pull' the --ff-only option will still check for forced updates
+	before attempting a fast-forward update. See linkgit:git-config[1].
+
 -4::
 --ipv4::
 	Use IPv4 addresses only, ignoring IPv6 addresses.
diff --git a/Documentation/git-status.txt b/Documentation/git-status.txt
index eec603fbfbe1cc..59f1e19cb94bff 100644
--- a/Documentation/git-status.txt
+++ b/Documentation/git-status.txt
@@ -152,6 +152,21 @@ ignored, then the directory is not shown, but all contents are shown.
 	update it afterwards if any changes were detected. Defaults to
 	`--lock-index`.
 
+--serialize[=<path>]::
+	(EXPERIMENTAL) Serialize raw status results to a file or stdout
+	in a format suitable for use by `--deserialize`.  If a path is
+	given, serialize data will be written to that path *and* normal
+	status output will be written to stdout.  If path is omitted,
+	only binary serialization data will be written to stdout.
+
+--deserialize[=<path>]::
+	(EXPERIMENTAL) Deserialize raw status results from a file or
+	stdin rather than scanning the worktree.  If `<path>` is omitted
+	and `status.deserializePath` is unset, input is read from stdin.
+--no-deserialize::
+	(EXPERIMENTAL) Disable implicit deserialization of status results
+	from the value of `status.deserializePath`.
+
 <pathspec>...::
 	See the 'pathspec' entry in linkgit:gitglossary[7].
 
@@ -389,6 +404,26 @@ quoted as explained for the configuration variable `core.quotePath`
 (see linkgit:git-config[1]).
 
 
+SERIALIZATION and DESERIALIZATION (EXPERIMENTAL)
+------------------------------------------------
+
+The `--serialize` option allows git to cache the result of a
+possibly time-consuming status scan to a binary file.  A local
+service/daemon watching file system events could use this to
+periodically pre-compute a fresh status result.
+
+Interactive users could then use `--deserialize` to simply
+(and immediately) print the last-known-good result without
+waiting for the status scan.
+
+The binary serialization file format includes some worktree state
+information allowing `--deserialize` to reject the cached data
+and force a normal status scan if, for example, the commit, branch,
+or status modes/options change.  The format cannot, however, indicate
+when the cached data is otherwise stale -- that coordination belongs
+to the task driving the serializations.
+
+
 CONFIGURATION
 -------------
 
diff --git a/Documentation/githooks.txt b/Documentation/githooks.txt
index 959044347e5ee0..1a90bc01d704c9 100644
--- a/Documentation/githooks.txt
+++ b/Documentation/githooks.txt
@@ -492,6 +492,44 @@ This hook is invoked by `git-p4 submit`. It takes no parameters and nothing
 from standard input. Exiting with non-zero status from this script prevent
 `git-p4 submit` from launching. Run `git-p4 submit --help` for details.
 
+virtualFilesystem
+~~~~~~~~~~~~~~~~~~
+
+"Virtual File System" allows populating the working directory sparsely.
+The projection data is typically automatically generated by an external
+process.  Git will limit what files it checks for changes as well as which
+directories are checked for untracked files based on the path names given.
+Git will also only update those files listed in the projection.
+
+The hook is invoked when the configuration option core.virtualFilesystem
+is set.  It takes one argument, a version (currently 1).
+
+The hook should output to stdout the list of all files in the working
+directory that git should track.  The paths are relative to the root
+of the working directory and are separated by a single NUL.  Full paths
+('dir1/a.txt') as well as directories are supported (ie 'dir1/').
+
+The exit status determines whether git will use the data from the
+hook.  On error, git will abort the command with an error message.
+
+post-indexchanged
+~~~~~~~~~~~~~~~~~
+
+This hook is invoked when the index is written in read-cache.c
+do_write_locked_index.
+
+The first parameter passed to the hook is the indicator for the
+working directory being updated.  "1" meaning working directory
+was updated or "0" when the working directory was not updated.
+
+The second parameter passed to the hook is the indicator for whether
+or not the index was updated and the skip-worktree bit could have
+changed.  "1" meaning skip-worktree bits could have been updated
+and "0" meaning they were not.
+
+Only one parameter should be set to "1" when the hook runs.  The hook
+running passing "1", "1" should not be possible.
+
 GIT
 ---
 Part of the linkgit:git[1] suite
diff --git a/Documentation/technical/read-object-protocol.txt b/Documentation/technical/read-object-protocol.txt
new file mode 100644
index 00000000000000..a893b46e7c28a9
--- /dev/null
+++ b/Documentation/technical/read-object-protocol.txt
@@ -0,0 +1,102 @@
+Read Object Process
+^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+The read-object process enables Git to read all missing blobs with a
+single process invocation for the entire life of a single Git command.
+This is achieved by using a packet format (pkt-line, see technical/
+protocol-common.txt) based protocol over standard input and standard
+output as follows. All packets, except for the "*CONTENT" packets and
+the "0000" flush packet, are considered text and therefore are
+terminated by a LF.
+
+Git starts the process when it encounters the first missing object that
+needs to be retrieved. After the process is started, Git sends a welcome
+message ("git-read-object-client"), a list of supported protocol version
+numbers, and a flush packet. Git expects to read a welcome response
+message ("git-read-object-server"), exactly one protocol version number
+from the previously sent list, and a flush packet. All further
+communication will be based on the selected version.
+
+The remaining protocol description below documents "version=1". Please
+note that "version=42" in the example below does not exist and is only
+there to illustrate how the protocol would look with more than one
+version.
+
+After the version negotiation Git sends a list of all capabilities that
+it supports and a flush packet. Git expects to read a list of desired
+capabilities, which must be a subset of the supported capabilities list,
+and a flush packet as response:
+------------------------
+packet: git> git-read-object-client
+packet: git> version=1
+packet: git> version=42
+packet: git> 0000
+packet: git< git-read-object-server
+packet: git< version=1
+packet: git< 0000
+packet: git> capability=get
+packet: git> capability=have
+packet: git> capability=put
+packet: git> capability=not-yet-invented
+packet: git> 0000
+packet: git< capability=get
+packet: git< 0000
+------------------------
+The only supported capability in version 1 is "get".
+
+Afterwards Git sends a list of "key=value" pairs terminated with a flush
+packet. The list will contain at least the command (based on the
+supported capabilities) and the sha1 of the object to retrieve. Please
+note, that the process must not send any response before it received the
+final flush packet.
+
+When the process receives the "get" command, it should make the requested
+object available in the git object store and then return success. Git will
+then check the object store again and this time find it and proceed.
+------------------------
+packet: git> command=get
+packet: git> sha1=0a214a649e1b3d5011e14a3dc227753f2bd2be05
+packet: git> 0000
+------------------------
+
+The process is expected to respond with a list of "key=value" pairs
+terminated with a flush packet. If the process does not experience
+problems then the list must contain a "success" status.
+------------------------
+packet: git< status=success
+packet: git< 0000
+------------------------
+
+In case the process cannot or does not want to process the content, it
+is expected to respond with an "error" status.
+------------------------
+packet: git< status=error
+packet: git< 0000
+------------------------
+
+In case the process cannot or does not want to process the content as
+well as any future content for the lifetime of the Git process, then it
+is expected to respond with an "abort" status at any point in the
+protocol.
+------------------------
+packet: git< status=abort
+packet: git< 0000
+------------------------
+
+Git neither stops nor restarts the process in case the "error"/"abort"
+status is set.
+
+If the process dies during the communication or does not adhere to the
+protocol then Git will stop the process and restart it with the next
+object that needs to be processed.
+
+After the read-object process has processed an object it is expected to
+wait for the next "key=value" list containing a command. Git will close
+the command pipe on exit. The process is expected to detect EOF and exit
+gracefully on its own. Git will wait until the process has stopped.
+
+A long running read-object process demo implementation can be found in
+`contrib/long-running-read-object/example.pl` located in the Git core
+repository. If you develop your own long running process then the
+`GIT_TRACE_PACKET` environment variables can be very helpful for
+debugging (see linkgit:git[1]).
diff --git a/Documentation/technical/status-serialization-format.txt b/Documentation/technical/status-serialization-format.txt
new file mode 100644
index 00000000000000..475ae814495581
--- /dev/null
+++ b/Documentation/technical/status-serialization-format.txt
@@ -0,0 +1,107 @@
+Git status serialization format
+===============================
+
+Git status serialization enables git to dump the results of a status scan
+to a binary file.  This file can then be loaded by later status invocations
+to print the cached status results.
+
+The file contains the essential fields from:
+() the index
+() the "struct wt_status" for the overall results
+() the contents of "struct wt_status_change_data" for tracked changed files
+() the list of untracked and ignored files
+
+Version 1 Format:
+=================
+
+The V1 file begins with a required header section followed by optional
+sections for each type of item (changed, untracked, ignored).  Individual
+item sections are only present if necessary.  Each item section begins
+with an item-type header with the number of items in the section.
+
+Each "line" in the format is encoded using pkt-line with a final LF.
+Flush packets are used to terminate sections.
+
+-----------------
+PKT-LINE("version" SP "1")
+<v1-header-section>
+[<v1-changed-item-section>]
+[<v1-untracked-item-section>]
+[<v1-ignored-item-section>]
+-----------------
+
+
+V1 Header
+---------
+
+The v1-header-section fields are taken directly from "struct wt_status".
+Each field is printed on a separate pkt-line.  Lines for NULL string
+values are omitted.  All integers are printed with "%d".  OIDs are
+printed in hex.
+
+v1-header-section    = <v1-index-headers>
+		       <v1-wt-status-headers>
+		       PKT-LINE(<flush>)
+
+v1-index-headers     = PKT-LINE("index_mtime" SP <sec> SP <nsec> LF)
+
+v1-wt-status-headers = PKT-LINE("is_initial" SP <integer> LF)
+		       [ PKT-LINE("branch" SP <branch-name> LF) ]
+		       [ PKT-LINE("reference" SP <reference-name> LF) ]
+		       PKT-LINE("show_ignored_files" SP <integer> LF)
+		       PKT-LINE("show_untracked_files" SP <integer> LF)
+		       PKT-LINE("show_ignored_directory" SP <integer> LF)
+		       [ PKT-LINE("ignore_submodule_arg" SP <string> LF) ]
+		       PKT-LINE("detect_rename" SP <integer> LF)
+		       PKT-LINE("rename_score" SP <integer> LF)
+		       PKT-LINE("rename_limit" SP <integer> LF)
+		       PKT-LINE("detect_break" SP <integer> LF)
+		       PKT-LINE("sha1_commit" SP <oid> LF)
+		       PKT-LINE("committable" SP <integer> LF)
+		       PKT-LINE("workdir_dirty" SP <integer> LF)
+
+
+V1 Changed Items
+----------------
+
+The v1-changed-item-section lists all of the changed items with one
+item per pkt-line.  Each pkt-line contains:  a binary block of data
+from "struct wt_status_serialize_data_fixed" in a fixed header where
+integers are in network byte order and OIDs are in raw (non-hex) form.
+This is followed by one or two raw pathnames (not c-quoted) with NUL
+terminators (both NULs are always present even if there is no rename).
+
+v1-changed-item-section = PKT-LINE("changed" SP <count> LF)
+			  [ PKT-LINE(<changed_item> LF) ]+
+			  PKT-LINE(<flush>)
+
+changed_item = <byte[4] worktree_status>
+	       <byte[4] index_status>
+	       <byte[4] stagemask>
+	       <byte[4] score>
+	       <byte[4] mode_head>
+	       <byte[4] mode_index>
+	       <byte[4] mode_worktree>
+	       <byte[4] dirty_submodule>
+	       <byte[4] new_submodule_commits>
+	       <byte[20] oid_head>
+	       <byte[20] oid_index>
+	       <byte[*] path>
+	       NUL
+	       [ <byte[*] src_path> ]
+	       NUL
+
+
+V1 Untracked and Ignored Items
+------------------------------
+
+These sections are simple lists of pathnames.  They ARE NOT
+c-quoted.
+
+v1-untracked-item-section = PKT-LINE("untracked" SP <count> LF)
+			    [ PKT-LINE(<pathname> LF) ]+
+			    PKT-LINE(<flush>)
+
+v1-ignored-item-section = PKT-LINE("ignored" SP <count> LF)
+			  [ PKT-LINE(<pathname> LF) ]+
+			  PKT-LINE(<flush>)
diff --git a/GIT-VERSION-GEN b/GIT-VERSION-GEN
index 216beefc50d54d..d91f4237d0b662 100755
--- a/GIT-VERSION-GEN
+++ b/GIT-VERSION-GEN
@@ -1,7 +1,7 @@
 #!/bin/sh
 
 GVF=GIT-VERSION-FILE
-DEF_VER=v2.20.0
+DEF_VER=v2.20.0.vfs.1.1
 
 LF='
 '
@@ -12,7 +12,7 @@ if test -f version
 then
 	VN=$(cat version) || VN="$DEF_VER"
 elif test -d ${GIT_DIR:-.git} -o -f .git &&
-	VN=$(git describe --match "v[0-9]*" HEAD 2>/dev/null) &&
+	VN=$(git describe --match "v[0-9]*vfs*" HEAD 2>/dev/null) &&
 	case "$VN" in
 	*$LF*) (exit 1) ;;
 	v[0-9]*)
diff --git a/Makefile b/Makefile
index 575c59d7ee0ddd..9e2a349c9106ef 100644
--- a/Makefile
+++ b/Makefile
@@ -896,6 +896,7 @@ LIB_OBJS += gettext.o
 LIB_OBJS += gpg-interface.o
 LIB_OBJS += graph.o
 LIB_OBJS += grep.o
+LIB_OBJS += gvfs.o
 LIB_OBJS += hashmap.o
 LIB_OBJS += linear-assignment.o
 LIB_OBJS += help.o
@@ -999,6 +1000,15 @@ LIB_OBJS += tempfile.o
 LIB_OBJS += thread-utils.o
 LIB_OBJS += tmp-objdir.o
 LIB_OBJS += trace.o
+LIB_OBJS += trace2.o
+LIB_OBJS += trace2/tr2_cfg.o
+LIB_OBJS += trace2/tr2_dst.o
+LIB_OBJS += trace2/tr2_sid.o
+LIB_OBJS += trace2/tr2_tbuf.o
+LIB_OBJS += trace2/tr2_tgt_event.o
+LIB_OBJS += trace2/tr2_tgt_normal.o
+LIB_OBJS += trace2/tr2_tgt_perf.o
+LIB_OBJS += trace2/tr2_tls.o
 LIB_OBJS += trailer.o
 LIB_OBJS += transport.o
 LIB_OBJS += transport-helper.o
@@ -1015,6 +1025,7 @@ LIB_OBJS += utf8.o
 LIB_OBJS += varint.o
 LIB_OBJS += version.o
 LIB_OBJS += versioncmp.o
+LIB_OBJS += virtualfilesystem.o
 LIB_OBJS += walker.o
 LIB_OBJS += wildmatch.o
 LIB_OBJS += worktree.o
@@ -1022,6 +1033,8 @@ LIB_OBJS += wrapper.o
 LIB_OBJS += write-or-die.o
 LIB_OBJS += ws.o
 LIB_OBJS += wt-status.o
+LIB_OBJS += wt-status-deserialize.o
+LIB_OBJS += wt-status-serialize.o
 LIB_OBJS += xdiff-interface.o
 LIB_OBJS += zlib.o
 
diff --git a/advice.c b/advice.c
index 5f35656409b1d5..a68d52d0328a81 100644
--- a/advice.c
+++ b/advice.c
@@ -11,6 +11,7 @@ int advice_push_fetch_first = 1;
 int advice_push_needs_force = 1;
 int advice_status_hints = 1;
 int advice_status_u_option = 1;
+int advice_status_ahead_behind_warning = 1;
 int advice_commit_before_merge = 1;
 int advice_reset_quiet_warning = 1;
 int advice_resolve_conflict = 1;
@@ -65,6 +66,7 @@ static struct {
 	{ "pushNeedsForce", &advice_push_needs_force },
 	{ "statusHints", &advice_status_hints },
 	{ "statusUoption", &advice_status_u_option },
+	{ "statusAheadBehindWarning", &advice_status_ahead_behind_warning },
 	{ "commitBeforeMerge", &advice_commit_before_merge },
 	{ "resetQuiet", &advice_reset_quiet_warning },
 	{ "resolveConflict", &advice_resolve_conflict },
diff --git a/advice.h b/advice.h
index 696bf0e7d29ee1..c2a35ad9eb1394 100644
--- a/advice.h
+++ b/advice.h
@@ -11,6 +11,7 @@ extern int advice_push_fetch_first;
 extern int advice_push_needs_force;
 extern int advice_status_hints;
 extern int advice_status_u_option;
+extern int advice_status_ahead_behind_warning;
 extern int advice_commit_before_merge;
 extern int advice_reset_quiet_warning;
 extern int advice_resolve_conflict;
diff --git a/apply.c b/apply.c
index 01793d61262024..73cac2c9b06c75 100644
--- a/apply.c
+++ b/apply.c
@@ -3350,6 +3350,24 @@ static int checkout_target(struct index_state *istate,
 {
 	struct checkout costate = CHECKOUT_INIT;
 
+	/*
+	 * Do not checkout the entry if the skipworktree bit is set
+	 *
+	 * Both callers of this method (check_preimage and load_current)
+	 * check for the existance of the file before calling this
+	 * method so we know that the file doesn't exist at this point
+	 * and we don't need to perform that check again here.
+	 * We just need to check the skip-worktree and return.
+	 *
+	 * This is to prevent git from creating a file in the
+	 * working directory that has the skip-worktree bit on,
+	 * then updating the index from the patch and not keeping
+	 * the working directory version up to date with what it
+	 * changed the index version to be.
+	 */
+	if (ce_skip_worktree(ce))
+		return 0;
+
 	costate.refresh_cache = 1;
 	costate.istate = istate;
 	if (checkout_entry(ce, &costate, NULL) || lstat(ce->name, st))
diff --git a/builtin/commit.c b/builtin/commit.c
index c74a0948afc2e4..03dfd4043442a9 100644
--- a/builtin/commit.c
+++ b/builtin/commit.c
@@ -142,6 +142,110 @@ static int opt_parse_porcelain(const struct option *opt, const char *arg, int un
 	return 0;
 }
 
+static int do_serialize = 0;
+static char *serialize_path = NULL;
+
+static int do_implicit_deserialize = 0;
+static int do_explicit_deserialize = 0;
+static char *deserialize_path = NULL;
+
+static enum wt_status_deserialize_wait implicit_deserialize_wait = DESERIALIZE_WAIT__UNSET;
+static enum wt_status_deserialize_wait explicit_deserialize_wait = DESERIALIZE_WAIT__UNSET;
+
+/*
+ * --serialize | --serialize=<path>
+ *
+ * Request that we serialize status output rather than or in addition to
+ * printing in any of the established formats.
+ *
+ * Without a path, we write binary serialization data to stdout (and omit
+ * the normal status output).
+ *
+ * With a path, we write binary serialization data to the <path> and then
+ * write normal status output.
+ */
+static int opt_parse_serialize(const struct option *opt, const char *arg, int unset)
+{
+	enum wt_status_format *value = (enum wt_status_format *)opt->value;
+	if (unset || !arg)
+		*value = STATUS_FORMAT_SERIALIZE_V1;
+
+	if (arg)
+		serialize_path = xstrdup(arg);
+
+	if (do_explicit_deserialize)
+		die("cannot mix --serialize and --deserialize");
+	do_implicit_deserialize = 0;
+
+	do_serialize = 1;
+	return 0;
+}
+
+/*
+ * --deserialize | --deserialize=<path> |
+ * --no-deserialize
+ *
+ * Request that we deserialize status data from some existing resource
+ * rather than performing a status scan.
+ *
+ * The input source can come from stdin or a path given here -- or be
+ * inherited from the config settings.
+ */
+static int opt_parse_deserialize(const struct option *opt, const char *arg, int unset)
+{
+	if (unset) {
+		do_implicit_deserialize = 0;
+		do_explicit_deserialize = 0;
+	} else {
+		if (do_serialize)
+			die("cannot mix --serialize and --deserialize");
+		if (arg) /* override config or stdin */
+			deserialize_path = xstrdup(arg);
+		if (deserialize_path && *deserialize_path
+		    && (access(deserialize_path, R_OK) != 0))
+			die("cannot find serialization file '%s'",
+			    deserialize_path);
+
+		do_explicit_deserialize = 1;
+	}
+
+	return 0;
+}
+
+static enum wt_status_deserialize_wait parse_dw(const char *arg)
+{
+	int tenths;
+
+	if (!strcmp(arg, "fail"))
+		return DESERIALIZE_WAIT__FAIL;
+	else if (!strcmp(arg, "block"))
+		return DESERIALIZE_WAIT__BLOCK;
+	else if (!strcmp(arg, "no"))
+		return DESERIALIZE_WAIT__NO;
+
+	/*
+	 * Otherwise, assume it is a timeout in tenths of a second.
+	 * If it contains a bogus value, atol() will return zero
+	 * which is OK.
+	 */
+	tenths = atol(arg);
+	if (tenths < 0)
+		tenths = DESERIALIZE_WAIT__NO;
+	return tenths;
+}
+
+static int opt_parse_deserialize_wait(const struct option *opt,
+				      const char *arg,
+				      int unset)
+{
+	if (unset)
+		explicit_deserialize_wait = DESERIALIZE_WAIT__UNSET;
+	else
+		explicit_deserialize_wait = parse_dw(arg);
+
+	return 0;
+}
+
 static int opt_parse_m(const struct option *opt, const char *arg, int unset)
 {
 	struct strbuf *buf = opt->value;
@@ -1035,6 +1139,8 @@ static void handle_untracked_files_arg(struct wt_status *s)
 		s->show_untracked_files = SHOW_NORMAL_UNTRACKED_FILES;
 	else if (!strcmp(untracked_files_arg, "all"))
 		s->show_untracked_files = SHOW_ALL_UNTRACKED_FILES;
+	else if (!strcmp(untracked_files_arg,"complete"))
+		s->show_untracked_files = SHOW_COMPLETE_UNTRACKED_FILES;
 	else
 		die(_("Invalid untracked files mode '%s'"), untracked_files_arg);
 }
@@ -1058,9 +1164,11 @@ static const char *read_commit_message(const char *name)
 static struct status_deferred_config {
 	enum wt_status_format status_format;
 	int show_branch;
+	enum ahead_behind_flags ahead_behind;
 } status_deferred_config = {
 	STATUS_FORMAT_UNSPECIFIED,
-	-1 /* unspecified */
+	-1, /* unspecified */
+	AHEAD_BEHIND_UNSPECIFIED,
 };
 
 static void finalize_deferred_config(struct wt_status *s)
@@ -1087,6 +1195,17 @@ static void finalize_deferred_config(struct wt_status *s)
 	if (s->show_branch < 0)
 		s->show_branch = 0;
 
+	/*
+	 * If the user did not give a "--[no]-ahead-behind" command
+	 * line argument *AND* we will print in a human-readable format
+	 * (short, long etc.) then we inherit from the status.aheadbehind
+	 * config setting.  In all other cases (and porcelain V[12] formats
+	 * in particular), we inherit _FULL for backwards compatibility.
+	 */
+	if (use_deferred_config &&
+	    s->ahead_behind_flags == AHEAD_BEHIND_UNSPECIFIED)
+		s->ahead_behind_flags = status_deferred_config.ahead_behind;
+
 	if (s->ahead_behind_flags == AHEAD_BEHIND_UNSPECIFIED)
 		s->ahead_behind_flags = AHEAD_BEHIND_FULL;
 }
@@ -1238,6 +1357,10 @@ static int git_status_config(const char *k, const char *v, void *cb)
 		status_deferred_config.show_branch = git_config_bool(k, v);
 		return 0;
 	}
+	if (!strcmp(k, "status.aheadbehind")) {
+		status_deferred_config.ahead_behind = git_config_bool(k, v);
+		return 0;
+	}
 	if (!strcmp(k, "status.showstash")) {
 		s->show_stash = git_config_bool(k, v);
 		return 0;
@@ -1263,6 +1386,26 @@ static int git_status_config(const char *k, const char *v, void *cb)
 		s->relative_paths = git_config_bool(k, v);
 		return 0;
 	}
+	if (!strcmp(k, "status.deserializepath")) {
+		/*
+		 * Automatically assume deserialization if this is
+		 * set in the config and the file exists.  Do not
+		 * complain if the file does not exist, because we
+		 * silently fall back to normal mode.
+		 */
+		if (v && *v && access(v, R_OK) == 0) {
+			do_implicit_deserialize = 1;
+			deserialize_path = xstrdup(v);
+		}
+		return 0;
+	}
+	if (!strcmp(k, "status.deserializewait")) {
+		if (!v || !*v)
+			implicit_deserialize_wait = DESERIALIZE_WAIT__UNSET;
+		else
+			implicit_deserialize_wait = parse_dw(v);
+		return 0;
+	}
 	if (!strcmp(k, "status.showuntrackedfiles")) {
 		if (!v)
 			return config_error_nonbool(k);
@@ -1305,7 +1448,8 @@ int cmd_status(int argc, const char **argv, const char *prefix)
 	static int show_ignored_directory = 0;
 	static struct wt_status s;
 	unsigned int progress_flag = 0;
-	int fd;
+	int try_deserialize;
+	int fd = -1;
 	struct object_id oid;
 	static struct option builtin_status_options[] = {
 		OPT__VERBOSE(&verbose, N_("be verbose")),
@@ -1320,6 +1464,15 @@ int cmd_status(int argc, const char **argv, const char *prefix)
 		{ OPTION_CALLBACK, 0, "porcelain", &status_format,
 		  N_("version"), N_("machine-readable output"),
 		  PARSE_OPT_OPTARG, opt_parse_porcelain },
+		{ OPTION_CALLBACK, 0, "serialize", &status_format,
+		  N_("path"), N_("serialize raw status data to path or stdout"),
+		  PARSE_OPT_OPTARG | PARSE_OPT_NONEG, opt_parse_serialize },
+		{ OPTION_CALLBACK, 0, "deserialize", NULL,
+		  N_("path"), N_("deserialize raw status data from file"),
+		  PARSE_OPT_OPTARG, opt_parse_deserialize },
+		{ OPTION_CALLBACK, 0, "deserialize-wait", NULL,
+		  N_("fail|block|no"), N_("how to wait if status cache file is invalid"),
+		  PARSE_OPT_OPTARG, opt_parse_deserialize_wait },
 		OPT_SET_INT(0, "long", &status_format,
 			    N_("show status in long format (default)"),
 			    STATUS_FORMAT_LONG),
@@ -1380,10 +1533,26 @@ int cmd_status(int argc, const char **argv, const char *prefix)
 	    s.show_untracked_files == SHOW_NO_UNTRACKED_FILES)
 		die(_("Unsupported combination of ignored and untracked-files arguments"));
 
+	if (s.show_untracked_files == SHOW_COMPLETE_UNTRACKED_FILES &&
+	    s.show_ignored_mode == SHOW_NO_IGNORED)
+		die(_("Complete Untracked only supported with ignored files"));
+
 	parse_pathspec(&s.pathspec, 0,
 		       PATHSPEC_PREFER_FULL,
 		       prefix, argv);
 
+	/*
+	 * If we want to try to deserialize status data from a cache file,
+	 * we need to re-order the initialization code.  The problem is that
+	 * this makes for a very nasty diff and causes merge conflicts as we
+	 * carry it forward.  And it easy to mess up the merge, so we
+	 * duplicate some code here to hopefully reduce conflicts.
+	 */
+	try_deserialize = (!do_serialize &&
+			   (do_implicit_deserialize || do_explicit_deserialize));
+	if (try_deserialize)
+		goto skip_init;
+
 	enable_fscache(0);
 	if (status_format != STATUS_FORMAT_PORCELAIN &&
 	    status_format != STATUS_FORMAT_PORCELAIN_V2)
@@ -1398,6 +1567,7 @@ int cmd_status(int argc, const char **argv, const char *prefix)
 	else
 		fd = -1;
 
+skip_init:
 	s.is_initial = get_oid(s.reference, &oid) ? 1 : 0;
 	if (!s.is_initial)
 		hashcpy(s.sha1_commit, oid.hash);
@@ -1414,6 +1584,34 @@ int cmd_status(int argc, const char **argv, const char *prefix)
 			s.rename_score = parse_rename_score(&rename_score_arg);
 	}
 
+	if (try_deserialize) {
+		int result;
+		enum wt_status_deserialize_wait dw = implicit_deserialize_wait;
+		if (explicit_deserialize_wait != DESERIALIZE_WAIT__UNSET)
+			dw = explicit_deserialize_wait;
+		if (dw == DESERIALIZE_WAIT__UNSET)
+			dw = DESERIALIZE_WAIT__NO;
+
+		if (s.relative_paths)
+			s.prefix = prefix;
+
+		result = wt_status_deserialize(&s, deserialize_path, dw);
+		if (result == DESERIALIZE_OK)
+			return 0;
+		if (dw == DESERIALIZE_WAIT__FAIL)
+			die(_("Rejected status serialization cache"));
+
+		/* deserialize failed, so force the initialization we skipped above. */
+		enable_fscache(1);
+		read_cache_preload(&s.pathspec);
+		refresh_index(&the_index, REFRESH_QUIET|REFRESH_UNMERGED, &s.pathspec, NULL, NULL);
+
+		if (use_optional_locks())
+			fd = hold_locked_index(&index_lock, 0);
+		else
+			fd = -1;
+	}
+
 	wt_status_collect(&s);
 
 	if (0 <= fd)
@@ -1422,6 +1620,16 @@ int cmd_status(int argc, const char **argv, const char *prefix)
 	if (s.relative_paths)
 		s.prefix = prefix;
 
+	if (serialize_path) {
+		int fd_serialize = xopen(serialize_path,
+					 O_WRONLY | O_CREAT | O_TRUNC, 0666);
+		if (fd_serialize < 0)
+			die_errno(_("could not serialize to '%s'"),
+				  serialize_path);
+		wt_status_serialize_v1(fd_serialize, &s);
+		close(fd_serialize);
+	}
+
 	wt_status_print(&s);
 	wt_status_collect_free_buffers(&s);
 
diff --git a/builtin/fetch.c b/builtin/fetch.c
index e0140327aab236..1ba858a34de6fc 100644
--- a/builtin/fetch.c
+++ b/builtin/fetch.c
@@ -24,6 +24,8 @@
 #include "list-objects-filter-options.h"
 #include "commit-reach.h"
 
+#define FORCED_UPDATES_DELAY_WARNING_IN_MS (10 * 1000)
+
 static const char * const builtin_fetch_usage[] = {
 	N_("git fetch [<options>] [<repository> [<refspec>...]]"),
 	N_("git fetch [<options>] <group>"),
@@ -39,6 +41,9 @@ enum {
 };
 
 static int fetch_prune_config = -1; /* unspecified */
+static int fetch_show_forced_updates = 1;
+static int fetch_show_forced_updates_warning = 0;
+static uint64_t forced_updates_ms = 0;
 static int prune = -1; /* unspecified */
 #define PRUNE_BY_DEFAULT 0 /* do we prune by default? */
 
@@ -79,6 +84,11 @@ static int git_fetch_config(const char *k, const char *v, void *cb)
 		return 0;
 	}
 
+	if (!strcmp(k, "fetch.showforcedupdates")) {
+		fetch_show_forced_updates = git_config_bool(k, v);
+		return 0;
+	}
+
 	if (!strcmp(k, "submodule.recurse")) {
 		int r = git_config_bool(k, v) ?
 			RECURSE_SUBMODULES_ON : RECURSE_SUBMODULES_OFF;
@@ -169,6 +179,8 @@ static struct option builtin_fetch_options[] = {
 	OPT_STRING_LIST(0, "negotiation-tip", &negotiation_tip, N_("revision"),
 			N_("report that we have only objects reachable from this object")),
 	OPT_PARSE_LIST_OBJECTS_FILTER(&filter_options),
+	OPT_BOOL(0, "show-forced-updates", &fetch_show_forced_updates,
+		 N_("check for forced-updates on all updated branches")),
 	OPT_END()
 };
 
@@ -696,6 +708,7 @@ static int update_local_ref(struct ref *ref,
 	enum object_type type;
 	struct branch *current_branch = branch_get(NULL);
 	const char *pretty_ref = prettify_refname(ref->name);
+	int fast_forward = 0;
 
 	type = oid_object_info(the_repository, &ref->new_oid, NULL);
 	if (type < 0)
@@ -773,9 +786,19 @@ static int update_local_ref(struct ref *ref,
 		return r;
 	}
 
-	if (in_merge_bases(current, updated)) {
+	if (fetch_show_forced_updates) {
+		uint64_t t_before = getnanotime();
+		fast_forward = in_merge_bases(current, updated);
+		forced_updates_ms += (getnanotime() - t_before) / 1000000;
+	} else {
+		fetch_show_forced_updates_warning = 1;
+		fast_forward = 1;
+	}
+
+	if (fast_forward) {
 		struct strbuf quickref = STRBUF_INIT;
 		int r;
+
 		strbuf_add_unique_abbrev(&quickref, &current->object.oid, DEFAULT_ABBREV);
 		strbuf_addstr(&quickref, "..");
 		strbuf_add_unique_abbrev(&quickref, &ref->new_oid, DEFAULT_ABBREV);
@@ -975,6 +998,17 @@ static int store_updated_refs(const char *raw_url, const char *remote_name,
 		      " 'git remote prune %s' to remove any old, conflicting "
 		      "branches"), remote_name);
 
+	if (!fetch_show_forced_updates && fetch_show_forced_updates_warning) {
+		warning(_("Fetch normally indicates which branches had a forced update, but that check has been disabled."));
+		warning(_("To re-enable, use '--show-forced-updates' flag or run 'git config fetch.showForcedUpdates true'."));
+	}
+	if (fetch_show_forced_updates &&
+	    forced_updates_ms > FORCED_UPDATES_DELAY_WARNING_IN_MS) {
+		warning(_("It took %.2f seconds to check forced updates. You can use '--no-show-forced-updates'\n"),
+			forced_updates_ms / 1000.0);
+		warning(_("or run 'git config fetch.showForcedUpdates false' to avoid this check.\n"));
+	}
+
  abort:
 	strbuf_release(&note);
 	free(url);
diff --git a/builtin/fsck.c b/builtin/fsck.c
index 3c3e0f06e78009..ada61b5d179808 100644
--- a/builtin/fsck.c
+++ b/builtin/fsck.c
@@ -48,6 +48,7 @@ static int name_objects;
 #define ERROR_PACK 04
 #define ERROR_REFS 010
 #define ERROR_COMMIT_GRAPH 020
+#define ERROR_MULTI_PACK_INDEX 040
 
 static const char *describe_object(struct object *obj)
 {
@@ -881,14 +882,14 @@ int cmd_fsck(int argc, const char **argv, const char *prefix)
 		midx_verify.argv = midx_argv;
 		midx_verify.git_cmd = 1;
 		if (run_command(&midx_verify))
-			errors_found |= ERROR_COMMIT_GRAPH;
+			errors_found |= ERROR_MULTI_PACK_INDEX;
 
 		prepare_alt_odb(the_repository);
 		for (alt =  the_repository->objects->alt_odb_list; alt; alt = alt->next) {
 			midx_argv[2] = "--object-dir";
 			midx_argv[3] = alt->path;
 			if (run_command(&midx_verify))
-				errors_found |= ERROR_COMMIT_GRAPH;
+				errors_found |= ERROR_MULTI_PACK_INDEX;
 		}
 	}
 
diff --git a/builtin/pack-objects.c b/builtin/pack-objects.c
index 411aefd6875b2d..25973b4dbb12b5 100644
--- a/builtin/pack-objects.c
+++ b/builtin/pack-objects.c
@@ -33,6 +33,7 @@
 #include "object-store.h"
 #include "dir.h"
 #include "midx.h"
+#include "trace2.h"
 
 #define IN_PACK(obj) oe_in_pack(&to_pack, obj)
 #define SIZE(obj) oe_size(&to_pack, obj)
@@ -3470,6 +3471,7 @@ int cmd_pack_objects(int argc, const char **argv, const char *prefix)
 		}
 	}
 
+	trace2_region_enter("pack-objects", "enumerate-objects", the_repository);
 	prepare_packing_data(&to_pack);
 
 	if (progress)
@@ -3484,12 +3486,20 @@ int cmd_pack_objects(int argc, const char **argv, const char *prefix)
 	if (include_tag && nr_result)
 		for_each_ref(add_ref_tag, NULL);
 	stop_progress(&progress_state);
+	trace2_region_leave("pack-objects", "enumerate-objects", the_repository);
 
 	if (non_empty && !nr_result)
 		return 0;
-	if (nr_result)
+	if (nr_result) {
+		trace2_region_enter("pack-objects", "prepare-pack", the_repository);
 		prepare_pack(window, depth);
+		trace2_region_leave("pack-objects", "prepare-pack", the_repository);
+	}
+
+	trace2_region_enter("pack-objects", "write-pack-file", the_repository);
 	write_pack_file();
+	trace2_region_leave("pack-objects", "write-pack-file", the_repository);
+
 	if (progress)
 		fprintf_ln(stderr,
 			   _("Total %"PRIu32" (delta %"PRIu32"),"
diff --git a/builtin/pull.c b/builtin/pull.c
index 1b90622b131118..6211df9777b90a 100644
--- a/builtin/pull.c
+++ b/builtin/pull.c
@@ -121,6 +121,7 @@ static char *opt_update_shallow;
 static char *opt_refmap;
 static char *opt_ipv4;
 static char *opt_ipv6;
+static int opt_show_forced_updates = -1;
 
 static struct option pull_options[] = {
 	/* Shared options */
@@ -232,6 +233,8 @@ static struct option pull_options[] = {
 	OPT_PASSTHRU('6',  "ipv6", &opt_ipv6, NULL,
 		N_("use IPv6 addresses only"),
 		PARSE_OPT_NOARG),
+	OPT_BOOL(0, "show-forced-updates", &opt_show_forced_updates,
+		 N_("check for forced-updates on all updated branches")),
 
 	OPT_END()
 };
@@ -540,6 +543,10 @@ static int run_fetch(const char *repo, const char **refspecs)
 		argv_array_push(&args, opt_ipv4);
 	if (opt_ipv6)
 		argv_array_push(&args, opt_ipv6);
+	if (opt_show_forced_updates > 0)
+		argv_array_push(&args, "--show-forced-updates");
+	else if (opt_show_forced_updates == 0)
+		argv_array_push(&args, "--no-show-forced-updates");
 
 	if (repo) {
 		argv_array_push(&args, repo);
diff --git a/builtin/rebase.c b/builtin/rebase.c
index 0fbeb5b95cf45a..b6ade2f821bc70 100644
--- a/builtin/rebase.c
+++ b/builtin/rebase.c
@@ -1114,13 +1114,17 @@ int cmd_rebase(int argc, const char **argv, const char *prefix)
 	 */
 
 	if (!use_builtin_rebase()) {
-		const char *path = mkpath("%s/git-legacy-rebase",
-					  git_exec_path());
-
-		if (sane_execvp(path, (char **)argv) < 0)
-			die_errno(_("could not exec %s"), path);
-		else
-			BUG("sane_execvp() returned???");
+		struct argv_array args = ARGV_ARRAY_INIT;
+		int code;
+
+		argv_array_push(&args, mkpath("%s/git-legacy-rebase",
+					      git_exec_path()));
+		argv_array_pushv(&args, argv + 1);
+		code = run_command_v_opt(args.argv, 0);
+		if (code < 0)
+			die_errno(_("could not exec %s"), args.argv[0]);
+		argv_array_clear(&args);
+		exit(code);
 	}
 
 	if (argc == 2 && !strcmp(argv[1], "-h"))
diff --git a/builtin/reset.c b/builtin/reset.c
index 4ba8badd0f72c4..32ba2e63f43dad 100644
--- a/builtin/reset.c
+++ b/builtin/reset.c
@@ -26,6 +26,7 @@
 #include "submodule-config.h"
 #include "strbuf.h"
 #include "quote.h"
+#include "dir.h"
 
 #define REFRESH_INDEX_DELAY_WARNING_IN_MS (2 * 1000)
 
@@ -127,12 +128,45 @@ static void update_index_from_diff(struct diff_queue_struct *q,
 		struct diff_options *opt, void *data)
 {
 	int i;
+	int pos;
 	int intent_to_add = *(int *)data;
 
 	for (i = 0; i < q->nr; i++) {
 		struct diff_filespec *one = q->queue[i]->one;
+		struct diff_filespec *two = q->queue[i]->two;
 		int is_missing = !(one->mode && !is_null_oid(&one->oid));
+		int was_missing = !two->mode && is_null_oid(&two->oid);
 		struct cache_entry *ce;
+		struct cache_entry *ceBefore;
+		struct checkout state = CHECKOUT_INIT;
+
+		/*
+		 * When using the sparse-checkout feature the cache entries that are
+		 * added here will not have the skip-worktree bit set.
+		 * Without this code there is data that is lost because the files that
+		 * would normally be in the working directory are not there and show as
+		 * deleted for the next status or in the case of added files just disappear.
+		 * We need to create the previous version of the files in the working
+		 * directory so that they will have the right content and the next
+		 * status call will show modified or untracked files correctly.
+		 */
+		if (core_apply_sparse_checkout && !file_exists(two->path))
+		{
+			pos = cache_name_pos(two->path, strlen(two->path));
+			if ((pos >= 0 && ce_skip_worktree(active_cache[pos])) && (is_missing || !was_missing))
+			{
+				state.force = 1;
+				state.refresh_cache = 1;
+				state.istate = &the_index;
+				ceBefore = make_cache_entry(&the_index, two->mode, &two->oid, two->path,
+					0, 0);
+				if (!ceBefore)
+					die(_("make_cache_entry failed for path '%s'"),
+						two->path);
+
+				checkout_entry(ceBefore, &state, NULL);
+			}
+		}
 
 		if (is_missing && !intent_to_add) {
 			remove_file_from_cache(one->path);
@@ -326,7 +360,7 @@ int cmd_reset(int argc, const char **argv, const char *prefix)
 
 	if (read_from_stdin) {
 		strbuf_getline_fn getline_fn = nul_term_line ?
-			strbuf_getline_nul : strbuf_getline_lf;
+			strbuf_getline_nul : strbuf_getline;
 		int flags = PATHSPEC_PREFER_FULL;
 		struct strbuf buf = STRBUF_INIT;
 		struct strbuf unquoted = STRBUF_INIT;
@@ -436,6 +470,7 @@ int cmd_reset(int argc, const char **argv, const char *prefix)
 						"use '--quiet' to avoid this.  Set the config setting reset.quiet to true\n"
 						"to make this the default.\n"), t_delta_in_ms / 1000.0);
 				}
+				the_index.updated_skipworktree = 1;
 			}
 		} else {
 			int err = reset_index(&oid, reset_type, quiet);
diff --git a/builtin/stash.c b/builtin/stash.c
index e5f1b0607d441b..ec159acecd5db2 100644
--- a/builtin/stash.c
+++ b/builtin/stash.c
@@ -1550,13 +1550,17 @@ int cmd_stash(int argc, const char **argv, const char *prefix)
 	};
 
 	if (!use_builtin_stash()) {
-		const char *path = mkpath("%s/git-legacy-stash",
-					  git_exec_path());
-
-		if (sane_execvp(path, (char **)argv) < 0)
-			die_errno(_("could not exec %s"), path);
-		else
-			BUG("sane_execvp() returned???");
+		struct argv_array args = ARGV_ARRAY_INIT;
+		int code;
+
+		argv_array_push(&args, mkpath("%s/git-legacy-stash",
+					      git_exec_path()));
+		argv_array_pushv(&args, argv + 1);
+		code = run_command_v_opt(args.argv, 0);
+		if (code < 0)
+			die_errno(_("could not exec %s"), args.argv[0]);
+		argv_array_clear(&args);
+		exit(code);
 	}
 
 	prefix = setup_git_directory();
diff --git a/builtin/update-index.c b/builtin/update-index.c
index 31e7cce3013a3b..64d8b373ecc8ac 100644
--- a/builtin/update-index.c
+++ b/builtin/update-index.c
@@ -1069,6 +1069,8 @@ int cmd_update_index(int argc, const char **argv, const char *prefix)
 	entries = read_cache();
 	if (entries < 0)
 		die("cache corrupted");
+	
+	the_index.updated_skipworktree = 1;
 
 	/*
 	 * Custom copy of parse_options() because we want to handle
diff --git a/cache-tree.c b/cache-tree.c
index 7361a42dedeb8e..2c0ce394b8fab0 100644
--- a/cache-tree.c
+++ b/cache-tree.c
@@ -5,6 +5,7 @@
 #include "cache-tree.h"
 #include "object-store.h"
 #include "replace-object.h"
+#include "gvfs.h"
 
 #ifndef DEBUG_CACHE_TREE
 #define DEBUG_CACHE_TREE 0
@@ -243,7 +244,8 @@ static int update_one(struct cache_tree *it,
 		      int flags)
 {
 	struct strbuf buffer;
-	int missing_ok = flags & WRITE_TREE_MISSING_OK;
+	int missing_ok = gvfs_config_is_set(GVFS_MISSING_OK) ?
+		WRITE_TREE_MISSING_OK : (flags & WRITE_TREE_MISSING_OK);
 	int dryrun = flags & WRITE_TREE_DRY_RUN;
 	int repair = flags & WRITE_TREE_REPAIR;
 	int to_invalidate = 0;
@@ -395,7 +397,29 @@ static int update_one(struct cache_tree *it,
 			continue;
 
 		strbuf_grow(&buffer, entlen + 100);
-		strbuf_addf(&buffer, "%o %.*s%c", mode, entlen, path + baselen, '\0');
+
+		switch (mode) {
+		case 0100644:
+			strbuf_add(&buffer, "100644 ", 7);
+			break;
+		case 0100664:
+			strbuf_add(&buffer, "100664 ", 7);
+			break;
+		case 0100755:
+			strbuf_add(&buffer, "100755 ", 7);
+			break;
+		case 0120000:
+			strbuf_add(&buffer, "120000 ", 7);
+			break;
+		case 0160000:
+			strbuf_add(&buffer, "160000 ", 7);
+			break;
+		default:
+			strbuf_addf(&buffer, "%o ", mode);
+			break;
+		}
+		strbuf_add(&buffer, path + baselen, entlen);
+		strbuf_addch(&buffer, '\0');
 		strbuf_add(&buffer, oid->hash, the_hash_algo->rawsz);
 
 #if DEBUG_CACHE_TREE
diff --git a/cache.h b/cache.h
index 7b6b89fc4c0c28..cf849fe505cd59 100644
--- a/cache.h
+++ b/cache.h
@@ -9,6 +9,7 @@
 #include "gettext.h"
 #include "convert.h"
 #include "trace.h"
+#include "trace2.h"
 #include "string-list.h"
 #include "pack-revindex.h"
 #include "hash.h"
@@ -328,7 +329,9 @@ struct index_state {
 	struct cache_time timestamp;
 	unsigned name_hash_initialized : 1,
 		 initialized : 1,
-		 drop_cache_tree : 1;
+		 drop_cache_tree : 1,
+		 updated_workdir : 1,
+		 updated_skipworktree : 1;
 	struct hashmap name_hash;
 	struct hashmap dir_hash;
 	struct object_id oid;
@@ -886,6 +889,8 @@ extern char *git_replace_ref_base;
 extern int fsync_object_files;
 extern int core_preload_index;
 extern int core_apply_sparse_checkout;
+extern const char *core_virtualfilesystem;
+extern int core_gvfs;
 extern int precomposed_unicode;
 extern int protect_hfs;
 extern int protect_ntfs;
@@ -911,6 +916,8 @@ int use_optional_locks(void);
 extern char comment_line_char;
 extern int auto_comment_line_char;
 
+extern int core_virtualize_objects;
+
 enum log_refs_config {
 	LOG_REFS_UNSET = -1,
 	LOG_REFS_NONE = 0,
@@ -1662,6 +1669,7 @@ extern void write_file(const char *path, const char *fmt, ...);
 
 /* pager.c */
 extern void setup_pager(void);
+extern void wait_for_pager_atexit(void);
 extern int pager_in_use(void);
 extern int pager_use_color;
 extern int term_columns(void);
diff --git a/commit.c b/commit.c
index d13a7bc3746406..e037d34bc1f9c2 100644
--- a/commit.c
+++ b/commit.c
@@ -583,7 +583,8 @@ void commit_list_sort_by_date(struct commit_list **list)
 }
 
 struct commit *pop_most_recent_commit(struct commit_list **list,
-				      unsigned int mark)
+				      unsigned int mark,
+				      uint32_t min_generation)
 {
 	struct commit *ret = pop_commit(list);
 	struct commit_list *parents = ret->parents;
@@ -592,7 +593,9 @@ struct commit *pop_most_recent_commit(struct commit_list **list,
 		struct commit *commit = parents->item;
 		if (!parse_commit(commit) && !(commit->object.flags & mark)) {
 			commit->object.flags |= mark;
-			commit_list_insert_by_date(commit, list);
+
+			if (commit->generation >= min_generation)
+				commit_list_insert_by_date(commit, list);
 		}
 		parents = parents->next;
 	}
diff --git a/commit.h b/commit.h
index 98664536cb82c6..b14a7fd2652299 100644
--- a/commit.h
+++ b/commit.h
@@ -166,9 +166,13 @@ extern const char *skip_blank_lines(const char *msg);
 
 /** Removes the first commit from a list sorted by date, and adds all
  * of its parents.
+ *
+ * The parents are not added if their generation number is strictly
+ * lower than min_generation.
  **/
 struct commit *pop_most_recent_commit(struct commit_list **list,
-				      unsigned int mark);
+				      unsigned int mark,
+				      uint32_t min_generation);
 
 struct commit *pop_commit(struct commit_list **stack);
 
diff --git a/common-main.c b/common-main.c
index 3728f66b4cce80..bfea45c18d82f3 100644
--- a/common-main.c
+++ b/common-main.c
@@ -31,6 +31,9 @@ int main(int argc, const char **argv)
 	 * onto stdin/stdout/stderr in the child processes we spawn.
 	 */
 	sanitize_stdfds();
+	restore_sigpipe_to_default();
+
+	trace2_initialize(argv);
 
 	git_resolve_executable_dir(argv[0]);
 
@@ -40,7 +43,5 @@ int main(int argc, const char **argv)
 
 	attr_start();
 
-	restore_sigpipe_to_default();
-
 	return cmd_main(argc, argv);
 }
diff --git a/compat/mingw.c b/compat/mingw.c
index 29c6c2cae9b444..53ad239cf03faa 100644
--- a/compat/mingw.c
+++ b/compat/mingw.c
@@ -1959,6 +1959,7 @@ static int try_shell_exec(const char *cmd, char *const *argv)
 			int status;
 			if (waitpid(pid, &status, 0) < 0)
 				status = 255;
+			trace2_exec_result(status);
 			exit(status);
 		}
 		pid = 1;	/* indicate that we tried but failed */
@@ -1979,6 +1980,7 @@ int mingw_execv(const char *cmd, char *const *argv)
 			return -1;
 		if (waitpid(pid, &status, 0) < 0)
 			status = 255;
+		trace2_exec_result(status);
 		exit(status);
 	}
 	return -1;
diff --git a/compat/mingw.h b/compat/mingw.h
index ea46b647f18835..e391497e8d10c4 100644
--- a/compat/mingw.h
+++ b/compat/mingw.h
@@ -165,8 +165,7 @@ static inline int fcntl(int fd, int cmd, ...)
 	errno = EINVAL;
 	return -1;
 }
-/* bash cannot reliably detect negative return codes as failure */
-#define exit(code) exit((code) & 0xff)
+
 #define sigemptyset(x) (void)0
 static inline int sigaddset(sigset_t *set, int signum)
 { return 0; }
diff --git a/config.c b/config.c
index f433b15b55c65c..95d3613702cf9b 100644
--- a/config.c
+++ b/config.c
@@ -19,6 +19,7 @@
 #include "utf8.h"
 #include "dir.h"
 #include "color.h"
+#include "gvfs.h"
 
 struct config_source {
 	struct config_source *prev;
@@ -1324,8 +1325,17 @@ static int git_default_core_config(const char *var, const char *value, void *cb)
 		return 0;
 	}
 
+	if (!strcmp(var, "core.gvfs")) {
+		gvfs_load_config_value(value);
+		return 0;
+	}
+
 	if (!strcmp(var, "core.sparsecheckout")) {
-		core_apply_sparse_checkout = git_config_bool(var, value);
+		/* virtual file system relies on the sparse checkout logic so force it on */
+		if (core_virtualfilesystem)
+			core_apply_sparse_checkout = 1;
+		else
+			core_apply_sparse_checkout = git_config_bool(var, value);
 		return 0;
 	}
 
@@ -1354,6 +1364,11 @@ static int git_default_core_config(const char *var, const char *value, void *cb)
 		return 0;
 	}
 
+	if (!strcmp(var, "core.virtualizeobjects")) {
+		core_virtualize_objects = git_config_bool(var, value);
+		return 0;
+	}
+
 	/* Add other config variables here and to Documentation/config.txt. */
 	return platform_core_config(var, value, cb);
 }
@@ -2301,6 +2316,37 @@ int git_config_get_fsmonitor(void)
 	return 0;
 }
 
+int git_config_get_virtualfilesystem(void)
+{
+	if (git_config_get_pathname("core.virtualfilesystem", &core_virtualfilesystem))
+		core_virtualfilesystem = getenv("GIT_VIRTUALFILESYSTEM_TEST");
+
+	if (core_virtualfilesystem && !*core_virtualfilesystem)
+		core_virtualfilesystem = NULL;
+
+	if (core_virtualfilesystem) {
+		/*
+		 * Some git commands spawn helpers and redirect the index to a different
+		 * location.  These include "difftool -d" and the sequencer
+		 * (i.e. `git rebase -i`, `git cherry-pick` and `git revert`) and others.
+		 * In those instances we don't want to update their temporary index with
+		 * our virtualization data.
+		 */
+		char *default_index_file = xstrfmt("%s/%s", the_repository->gitdir, "index");
+		int should_run_hook = !strcmp(default_index_file, the_repository->index_file);
+
+		free(default_index_file);
+		if (should_run_hook) {
+			/* virtual file system relies on the sparse checkout logic so force it on */
+			core_apply_sparse_checkout = 1;
+			return 1;
+		} 
+		core_virtualfilesystem = NULL;
+	}
+
+	return 0;
+}
+
 int git_config_get_index_threads(int *dest)
 {
 	int is_bool, val;
@@ -2663,6 +2709,8 @@ int git_config_set_gently(const char *key, const char *value)
 void git_config_set(const char *key, const char *value)
 {
 	git_config_set_multivar(key, value, NULL, 0);
+
+	trace2_cmd_set_config(key, value);
 }
 
 /*
diff --git a/config.h b/config.h
index ee5d3fa7b4264f..66ea920660f777 100644
--- a/config.h
+++ b/config.h
@@ -251,6 +251,7 @@ extern int git_config_get_untracked_cache(void);
 extern int git_config_get_split_index(void);
 extern int git_config_get_max_percent_split_change(void);
 extern int git_config_get_fsmonitor(void);
+extern int git_config_get_virtualfilesystem(void);
 
 /* This dies if the configured or default date is in the future */
 extern int git_config_get_expiry(const char *key, const char **output);
diff --git a/connect.c b/connect.c
index d72772a36d01ff..75202e81a23157 100644
--- a/connect.c
+++ b/connect.c
@@ -1255,6 +1255,7 @@ struct child_process *git_connect(int fd[2], const char *url,
 		conn = NULL;
 	} else if (protocol == PROTO_GIT) {
 		conn = git_connect_git(fd, hostandport, path, prog, version, flags);
+		conn->trace2_child_class = "transport/git";
 	} else {
 		struct strbuf cmd = STRBUF_INIT;
 		const char *const *var;
@@ -1297,9 +1298,11 @@ struct child_process *git_connect(int fd[2], const char *url,
 				strbuf_release(&cmd);
 				return NULL;
 			}
+			conn->trace2_child_class = "transport/ssh";
 			fill_ssh_args(conn, ssh_host, port, version, flags);
 		} else {
 			transport_check_allowed("file");
+			conn->trace2_child_class = "transport/file";
 			if (version > 0) {
 				argv_array_pushf(&conn->env_array, GIT_PROTOCOL_ENVIRONMENT "=version=%d",
 						 version);
diff --git a/connected.c b/connected.c
index 1bba888eff90a2..078ec309572b4e 100644
--- a/connected.c
+++ b/connected.c
@@ -4,6 +4,7 @@
 #include "connected.h"
 #include "transport.h"
 #include "packfile.h"
+#include "gvfs.h"
 
 /*
  * If we feed all the commits we want to verify to this command
@@ -28,6 +29,26 @@ int check_connected(oid_iterate_fn fn, void *cb_data,
 	struct transport *transport;
 	size_t base_len;
 
+	/*
+	 * Running a virtual file system there will be objects that are
+	 * missing locally and we don't want to download a bunch of
+	 * commits, trees, and blobs just to make sure everything is
+	 * reachable locally so this option will skip reachablility
+	 * checks below that use rev-list.  This will stop the check
+	 * before uploadpack runs to determine if there is anything to
+	 * fetch.  Returning zero for the first check will also prevent the
+	 * uploadpack from happening.  It will also skip the check after
+	 * the fetch is finished to make sure all the objects where
+	 * downloaded in the pack file.  This will allow the fetch to
+	 * run and get all the latest tip commit ids for all the branches
+	 * in the fetch but not pull down commits, trees, or blobs via
+	 * upload pack.
+	 */
+	if (gvfs_config_is_set(GVFS_FETCH_SKIP_REACHABILITY_AND_UPLOADPACK))
+		return 0;
+	if (core_virtualize_objects)
+		return 0;
+
 	if (!opt)
 		opt = &defaults;
 	transport = opt->transport;
diff --git a/contrib/long-running-read-object/example.pl b/contrib/long-running-read-object/example.pl
new file mode 100644
index 00000000000000..b8f37f836a813c
--- /dev/null
+++ b/contrib/long-running-read-object/example.pl
@@ -0,0 +1,114 @@
+#!/usr/bin/perl
+#
+# Example implementation for the Git read-object protocol version 1
+# See Documentation/technical/read-object-protocol.txt
+#
+# Allows you to test the ability for blobs to be pulled from a host git repo
+# "on demand."  Called when git needs a blob it couldn't find locally due to
+# a lazy clone that only cloned the commits and trees.
+#
+# A lazy clone can be simulated via the following commands from the host repo
+# you wish to create a lazy clone of:
+#
+# cd /host_repo
+# git rev-parse HEAD
+# git init /guest_repo
+# git cat-file --batch-check --batch-all-objects | grep -v 'blob' |
+#	cut -d' ' -f1 | git pack-objects /guest_repo/.git/objects/pack/noblobs
+# cd /guest_repo
+# git config core.virtualizeobjects true
+# git reset --hard <sha from rev-parse call above>
+#
+# Please note, this sample is a minimal skeleton. No proper error handling
+# was implemented.
+#
+
+use strict;
+use warnings;
+
+#
+# Point $DIR to the folder where your host git repo is located so we can pull
+# missing objects from it
+#
+my $DIR = "/host_repo/.git/";
+
+sub packet_bin_read {
+	my $buffer;
+	my $bytes_read = read STDIN, $buffer, 4;
+	if ( $bytes_read == 0 ) {
+
+		# EOF - Git stopped talking to us!
+		exit();
+	}
+	elsif ( $bytes_read != 4 ) {
+		die "invalid packet: '$buffer'";
+	}
+	my $pkt_size = hex($buffer);
+	if ( $pkt_size == 0 ) {
+		return ( 1, "" );
+	}
+	elsif ( $pkt_size > 4 ) {
+		my $content_size = $pkt_size - 4;
+		$bytes_read = read STDIN, $buffer, $content_size;
+		if ( $bytes_read != $content_size ) {
+			die "invalid packet ($content_size bytes expected; $bytes_read bytes read)";
+		}
+		return ( 0, $buffer );
+	}
+	else {
+		die "invalid packet size: $pkt_size";
+	}
+}
+
+sub packet_txt_read {
+	my ( $res, $buf ) = packet_bin_read();
+	unless ( $buf =~ s/\n$// ) {
+		die "A non-binary line MUST be terminated by an LF.";
+	}
+	return ( $res, $buf );
+}
+
+sub packet_bin_write {
+	my $buf = shift;
+	print STDOUT sprintf( "%04x", length($buf) + 4 );
+	print STDOUT $buf;
+	STDOUT->flush();
+}
+
+sub packet_txt_write {
+	packet_bin_write( $_[0] . "\n" );
+}
+
+sub packet_flush {
+	print STDOUT sprintf( "%04x", 0 );
+	STDOUT->flush();
+}
+
+( packet_txt_read() eq ( 0, "git-read-object-client" ) ) || die "bad initialize";
+( packet_txt_read() eq ( 0, "version=1" ) )				 || die "bad version";
+( packet_bin_read() eq ( 1, "" ) )                       || die "bad version end";
+
+packet_txt_write("git-read-object-server");
+packet_txt_write("version=1");
+packet_flush();
+
+( packet_txt_read() eq ( 0, "capability=get" ) )    || die "bad capability";
+( packet_bin_read() eq ( 1, "" ) )                  || die "bad capability end";
+
+packet_txt_write("capability=get");
+packet_flush();
+
+while (1) {
+	my ($command) = packet_txt_read() =~ /^command=([^=]+)$/;
+
+	if ( $command eq "get" ) {
+		my ($sha1) = packet_txt_read() =~ /^sha1=([0-9a-f]{40})$/;
+		packet_bin_read();
+
+		system ('git --git-dir="' . $DIR . '" cat-file blob ' . $sha1 . ' | git -c core.virtualizeobjects=false hash-object -w --stdin >/dev/null 2>&1');
+		packet_txt_write(($?) ? "status=error" : "status=success");
+		packet_flush();
+	} else {
+		die "bad command '$command'";
+	}
+}
diff --git a/convert.c b/convert.c
index e0848226d21bbb..ba34b9195c963e 100644
--- a/convert.c
+++ b/convert.c
@@ -9,6 +9,7 @@
 #include "pkt-line.h"
 #include "sub-process.h"
 #include "utf8.h"
+#include "gvfs.h"
 
 /*
  * convert.c - convert a file when checking it out and checking it in.
@@ -565,6 +566,9 @@ static int crlf_to_git(const struct index_state *istate,
 	if (!buf)
 		return 1;
 
+	if (gvfs_config_is_set(GVFS_BLOCK_FILTERS_AND_EOL_CONVERSIONS))
+		die("CRLF conversions not supported when running under GVFS");
+
 	/* only grow if not in place */
 	if (strbuf_avail(buf) + buf->len < len)
 		strbuf_grow(buf, len - buf->len);
@@ -604,6 +608,9 @@ static int crlf_to_worktree(const char *path, const char *src, size_t len,
 	if (!will_convert_lf_to_crlf(len, &stats, crlf_action))
 		return 0;
 
+	if (gvfs_config_is_set(GVFS_BLOCK_FILTERS_AND_EOL_CONVERSIONS))
+		die("CRLF conversions not supported when running under GVFS");
+
 	/* are we "faking" in place editing ? */
 	if (src == buf->buf)
 		to_free = strbuf_detach(buf, NULL);
@@ -718,6 +725,9 @@ static int apply_single_file_filter(const char *path, const char *src, size_t le
 	struct async async;
 	struct filter_params params;
 
+	if (gvfs_config_is_set(GVFS_BLOCK_FILTERS_AND_EOL_CONVERSIONS))
+		die("Filter \"%s\" not supported when running under GVFS", cmd);
+
 	memset(&async, 0, sizeof(async));
 	async.proc = filter_buffer_or_fd;
 	async.data = &params;
@@ -1101,6 +1111,9 @@ static int ident_to_git(const char *path, const char *src, size_t len,
 	if (!buf)
 		return 1;
 
+	if (gvfs_config_is_set(GVFS_BLOCK_FILTERS_AND_EOL_CONVERSIONS))
+		die("ident conversions not supported when running under GVFS");
+
 	/* only grow if not in place */
 	if (strbuf_avail(buf) + buf->len < len)
 		strbuf_grow(buf, len - buf->len);
@@ -1148,6 +1161,9 @@ static int ident_to_worktree(const char *path, const char *src, size_t len,
 	if (!cnt)
 		return 0;
 
+	if (gvfs_config_is_set(GVFS_BLOCK_FILTERS_AND_EOL_CONVERSIONS))
+		die("ident conversions not supported when running under GVFS");
+
 	/* are we "faking" in place editing ? */
 	if (src == buf->buf)
 		to_free = strbuf_detach(buf, NULL);
diff --git a/dir.c b/dir.c
index ca1e9f1bf18981..d7d8b6fbe38565 100644
--- a/dir.c
+++ b/dir.c
@@ -21,6 +21,7 @@
 #include "ewah/ewok.h"
 #include "fsmonitor.h"
 #include "submodule-config.h"
+#include "virtualfilesystem.h"
 
 /*
  * Tells read_directory_recursive how a file or directory should be treated.
@@ -1159,6 +1160,18 @@ int is_excluded_from_list(const char *pathname,
 			  struct exclude_list *el, struct index_state *istate)
 {
 	struct exclude *exclude;
+
+	/*
+	 * The virtual file system data is used to prevent git from traversing
+	 * any part of the tree that is not in the virtual file system.  Return
+	 * 1 to exclude the entry if it is not found in the virtual file system,
+	 * else fall through to the regular excludes logic as it may further exclude.
+	 */
+	if (*dtype == DT_UNKNOWN)
+		*dtype = get_dtype(NULL, istate, pathname, pathlen);
+	if (is_excluded_from_virtualfilesystem(pathname, pathlen, *dtype) > 0)
+		return 1;
+
 	exclude = last_exclude_matching_from_list(pathname, pathlen, basename,
 						  dtype, el, istate);
 	if (exclude)
@@ -1374,8 +1387,20 @@ struct exclude *last_exclude_matching(struct dir_struct *dir,
 int is_excluded(struct dir_struct *dir, struct index_state *istate,
 		const char *pathname, int *dtype_p)
 {
-	struct exclude *exclude =
-		last_exclude_matching(dir, istate, pathname, dtype_p);
+	struct exclude *exclude;
+
+	/*
+	 * The virtual file system data is used to prevent git from traversing
+	 * any part of the tree that is not in the virtual file system.  Return
+	 * 1 to exclude the entry if it is not found in the virtual file system,
+	 * else fall through to the regular excludes logic as it may further exclude.
+	 */
+	if (*dtype_p == DT_UNKNOWN)
+		*dtype_p = get_dtype(NULL, istate, pathname, strlen(pathname));
+	if (is_excluded_from_virtualfilesystem(pathname, strlen(pathname), *dtype_p) > 0)
+		return 1;
+
+	exclude = last_exclude_matching(dir, istate, pathname, dtype_p);
 	if (exclude)
 		return exclude->flags & EXC_FLAG_NEGATIVE ? 0 : 1;
 	return 0;
@@ -1728,6 +1753,9 @@ static enum path_treatment treat_one_path(struct dir_struct *dir,
 	if (dtype != DT_DIR && has_path_in_index)
 		return path_none;
 
+	if (is_excluded_from_virtualfilesystem(path->buf, path->len, dtype) > 0)
+		return path_excluded;
+
 	/*
 	 * When we are looking at a directory P in the working tree,
 	 * there are three cases:
@@ -2068,6 +2096,8 @@ static enum path_treatment read_directory_recursive(struct dir_struct *dir,
 		/* add the path to the appropriate result list */
 		switch (state) {
 		case path_excluded:
+			if (is_excluded_from_virtualfilesystem(path.buf, path.len, DT_DIR) > 0)
+				break;
 			if (dir->flags & DIR_SHOW_IGNORED)
 				dir_add_name(dir, istate, path.buf, path.len);
 			else if ((dir->flags & DIR_SHOW_IGNORED_TOO) ||
diff --git a/editor.c b/editor.c
index c985eee1f9d1c7..71547674ab4e88 100644
--- a/editor.c
+++ b/editor.c
@@ -78,6 +78,7 @@ static int launch_specified_editor(const char *editor, const char *path,
 		p.argv = args;
 		p.env = env;
 		p.use_shell = 1;
+		p.trace2_child_class = "editor";
 		if (start_command(&p) < 0)
 			return error("unable to start editor '%s'", editor);
 
diff --git a/environment.c b/environment.c
index 346559770773e9..cfa54e99e2031f 100644
--- a/environment.c
+++ b/environment.c
@@ -69,9 +69,12 @@ enum object_creation_mode object_creation_mode = OBJECT_CREATION_MODE;
 char *notes_ref_name;
 int grafts_replace_parents = 1;
 int core_apply_sparse_checkout;
+int core_gvfs;
+const char *core_virtualfilesystem;
 int merge_log_config = -1;
 int precomposed_unicode = -1; /* see probe_utf8_pathname_composition() */
 unsigned long pack_size_limit_cfg;
+int core_virtualize_objects;
 enum log_refs_config log_all_ref_updates = LOG_REFS_UNSET;
 
 #ifndef PROTECT_HFS_DEFAULT
diff --git a/exec-cmd.c b/exec-cmd.c
index 4f81f443105f07..640003564e611c 100644
--- a/exec-cmd.c
+++ b/exec-cmd.c
@@ -209,6 +209,8 @@ static int git_get_exec_path(struct strbuf *buf, const char *argv0)
 		return -1;
 	}
 
+	trace2_cmd_path(buf->buf);
+
 	return 0;
 }
 
@@ -328,16 +330,22 @@ const char **prepare_git_cmd(struct argv_array *out, const char **argv)
 int execv_git_cmd(const char **argv)
 {
 	struct argv_array nargv = ARGV_ARRAY_INIT;
+	int err;
 
 	prepare_git_cmd(&nargv, argv);
 	trace_argv_printf(nargv.argv, "trace: exec:");
+	trace2_exec("git", (const char **)nargv.argv);
 
 	/* execvp() can only ever return if it fails */
 	sane_execvp("git", (char **)nargv.argv);
 
-	trace_printf("trace: exec failed: %s\n", strerror(errno));
+	err = errno;
+	trace_printf("trace: exec failed: %s\n", strerror(err));
+	trace2_exec_result(err);
 
 	argv_array_clear(&nargv);
+
+	errno = err;
 	return -1;
 }
 
diff --git a/fetch-pack.c b/fetch-pack.c
index b71572292d65a8..174ff6a4a0a9d2 100644
--- a/fetch-pack.c
+++ b/fetch-pack.c
@@ -521,7 +521,8 @@ static void mark_recent_complete_commits(struct fetch_pack_args *args,
 	while (complete && cutoff <= complete->item->date) {
 		print_verbose(args, _("Marking %s as complete"),
 			      oid_to_hex(&complete->item->object.oid));
-		pop_most_recent_commit(&complete, COMPLETE);
+		pop_most_recent_commit(&complete, COMPLETE,
+				       GENERATION_NUMBER_ZERO);
 	}
 }
 
diff --git a/git-compat-util.h b/git-compat-util.h
index e6be418b4ee2f2..e7aa57730911e7 100644
--- a/git-compat-util.h
+++ b/git-compat-util.h
@@ -1291,6 +1291,13 @@ struct fscache;
 
 extern int cmd_main(int, const char **);
 
+/*
+ * Intercept all calls to exit() and route them to trace2 to
+ * optionally emit a message before calling the real exit().
+ */
+int trace2_cmd_exit_fl(const char *file, int line, int code);
+#define exit(code) exit(trace2_cmd_exit_fl(__FILE__, __LINE__, (code)))
+
 /*
  * You can mark a stack variable with UNLEAK(var) to avoid it being
  * reported as a leak by tools like LSAN or valgrind. The argument
diff --git a/git.c b/git.c
index 2c5d6d67118886..f3cd1b9f3d3d84 100644
--- a/git.c
+++ b/git.c
@@ -4,6 +4,7 @@
 #include "help.h"
 #include "run-command.h"
 #include "alias.h"
+#include "dir.h"
 
 #define RUN_SETUP		(1<<0)
 #define RUN_SETUP_GENTLY	(1<<1)
@@ -146,16 +147,20 @@ static int handle_options(const char ***argv, int *argc, int *envchanged)
 				git_set_exec_path(cmd + 1);
 			else {
 				puts(git_exec_path());
+				trace2_cmd_verb("_query_");
 				exit(0);
 			}
 		} else if (!strcmp(cmd, "--html-path")) {
 			puts(system_path(GIT_HTML_PATH));
+			trace2_cmd_verb("_query_");
 			exit(0);
 		} else if (!strcmp(cmd, "--man-path")) {
 			puts(system_path(GIT_MAN_PATH));
+			trace2_cmd_verb("_query_");
 			exit(0);
 		} else if (!strcmp(cmd, "--info-path")) {
 			puts(system_path(GIT_INFO_PATH));
+			trace2_cmd_verb("_query_");
 			exit(0);
 		} else if (!strcmp(cmd, "-p") || !strcmp(cmd, "--paginate")) {
 			use_pager = 1;
@@ -284,6 +289,7 @@ static int handle_options(const char ***argv, int *argc, int *envchanged)
 			(*argv)++;
 			(*argc)--;
 		} else if (skip_prefix(cmd, "--list-cmds=", &cmd)) {
+			trace2_cmd_verb("_query_");
 			if (!strcmp(cmd, "parseopt")) {
 				struct string_list list = STRING_LIST_INIT_DUP;
 				int i;
@@ -331,9 +337,14 @@ static int handle_alias(int *argcp, const char ***argv)
 			commit_pager_choice();
 
 			child.use_shell = 1;
+			child.trace2_child_class = "shell_alias";
 			argv_array_push(&child.args, alias_string + 1);
 			argv_array_pushv(&child.args, (*argv) + 1);
 
+			trace2_cmd_alias(alias_command, child.args.argv);
+			trace2_cmd_list_config();
+			trace2_cmd_verb("_run_shell_alias_");
+
 			ret = run_command(&child);
 			if (ret >= 0)   /* normal exit */
 				exit(ret);
@@ -368,6 +379,9 @@ static int handle_alias(int *argcp, const char ***argv)
 		/* insert after command name */
 		memcpy(new_argv + count, *argv + 1, sizeof(char *) * *argcp);
 
+		trace2_cmd_alias(alias_command, new_argv);
+		trace2_cmd_list_config();
+
 		*argv = new_argv;
 		*argcp += count - 1;
 
@@ -379,6 +393,64 @@ static int handle_alias(int *argcp, const char ***argv)
 	return ret;
 }
 
+/* Runs pre/post-command hook */
+static struct argv_array sargv = ARGV_ARRAY_INIT;
+static int run_post_hook = 0;
+static int exit_code = -1;
+
+static int run_pre_command_hook(const char **argv)
+{
+	char *lock;
+	int ret = 0;
+
+	/*
+	 * Ensure the global pre/post command hook is only called for
+	 * the outer command and not when git is called recursively
+	 * or spawns multiple commands (like with the alias command)
+	 */
+	lock = getenv("COMMAND_HOOK_LOCK");
+	if (lock && !strcmp(lock, "true"))
+		return 0;
+	setenv("COMMAND_HOOK_LOCK", "true", 1);
+
+	/* call the hook proc */
+	argv_array_pushv(&sargv, argv);
+	argv_array_pushf(&sargv, "--git-pid=%"PRIuMAX, (uintmax_t)getpid());
+	ret = run_hook_argv(NULL, "pre-command", sargv.argv);
+
+	if (!ret)
+		run_post_hook = 1;
+	return ret;
+}
+
+static int run_post_command_hook(void)
+{
+	char *lock;
+	int ret = 0;
+
+	/*
+	 * Only run post_command if pre_command succeeded in this process
+	 */
+	if (!run_post_hook)
+		return 0;
+	lock = getenv("COMMAND_HOOK_LOCK");
+	if (!lock || strcmp(lock, "true"))
+		return 0;
+
+	argv_array_pushf(&sargv, "--exit_code=%u", exit_code);
+	ret = run_hook_argv(NULL, "post-command", sargv.argv);
+
+	run_post_hook = 0;
+	argv_array_clear(&sargv);
+	setenv("COMMAND_HOOK_LOCK", "false", 1);
+	return ret;
+}
+
+static void post_command_hook_atexit(void)
+{
+	run_post_command_hook();
+}
+
 static int run_builtin(struct cmd_struct *p, int argc, const char **argv)
 {
 	int status, help;
@@ -415,15 +487,22 @@ static int run_builtin(struct cmd_struct *p, int argc, const char **argv)
 	if (!help && p->option & NEED_WORK_TREE)
 		setup_work_tree();
 
+	if (run_pre_command_hook(argv))
+		die("pre-command hook aborted command");
+
 	trace_argv_printf(argv, "trace: built-in: git");
+	trace2_cmd_verb(p->cmd);
+	trace2_cmd_list_config();
 
 	validate_cache_entries(&the_index);
-	status = p->fn(argc, argv, prefix);
+	exit_code = status = p->fn(argc, argv, prefix);
 	validate_cache_entries(&the_index);
 
 	if (status)
 		return status;
 
+	run_post_command_hook();
+
 	/* Somebody closed stdout? */
 	if (fstat(fileno(stdout), &st))
 		return 0;
@@ -671,20 +750,36 @@ static void execv_dashed_external(const char **argv)
 	cmd.clean_on_exit = 1;
 	cmd.wait_after_clean = 1;
 	cmd.silent_exec_failure = 1;
+	cmd.trace2_child_class = "dashed";
+
+	if (run_pre_command_hook(cmd.args.argv))
+		die("pre-command hook aborted command");
 
 	trace_argv_printf(cmd.args.argv, "trace: exec:");
+	trace2_exec(NULL, cmd.args.argv);
 
 	/*
 	 * If we fail because the command is not found, it is
 	 * OK to return. Otherwise, we just pass along the status code,
 	 * or our usual generic code if we were not even able to exec
 	 * the program.
+	 *
+	 * If the child process ran and we are now going to exit, emit a
+	 * generic string as our trace2 command verb to indicate that we
+	 * launched a dashed command.
 	 */
-	status = run_command(&cmd);
-	if (status >= 0)
+	exit_code = status = run_command(&cmd);
+	trace2_exec_result(status);
+	if (status >= 0) {
+		trace2_cmd_verb("_run_dashed_");
 		exit(status);
-	else if (errno != ENOENT)
+	}
+	else if (errno != ENOENT) {
+		trace2_cmd_verb("_run_dashed_");
 		exit(128);
+	}
+
+	run_post_command_hook();
 }
 
 static int run_argv(int *argcp, const char ***argv)
@@ -709,6 +804,15 @@ static int run_argv(int *argcp, const char ***argv)
 			struct argv_array args = ARGV_ARRAY_INIT;
 			int i;
 
+			/*
+			 * The current process is committed to launching a
+			 * child process to run the command named in (**argv)
+			 * and exiting.  Log a generic string as the trace2
+			 * command verb to indicate this.  Note that the child
+			 * process will log the actual verb when it runs.
+			 */
+			trace2_cmd_verb("_run_git_alias_");
+
 			if (get_super_prefix())
 				die("%s doesn't support --super-prefix", **argv);
 
@@ -724,8 +828,8 @@ static int run_argv(int *argcp, const char ***argv)
 			 * if we fail because the command is not found, it is
 			 * OK to return. Otherwise, we just pass along the status code.
 			 */
-			i = run_command_v_opt(args.argv, RUN_SILENT_EXEC_FAILURE |
-					      RUN_CLEAN_ON_EXIT);
+			i = run_command_v_opt_tr2(args.argv, RUN_SILENT_EXEC_FAILURE |
+						  RUN_CLEAN_ON_EXIT, "git_alias");
 			if (i >= 0 || errno != ENOENT)
 				exit(i);
 			die("could not execute builtin %s", **argv);
@@ -782,7 +886,14 @@ int cmd_main(int argc, const char **argv)
 			cmd = slash + 1;
 	}
 
+	/*
+	 * wait_for_pager_atexit will close stdout/stderr so it needs to be
+	 * registered first so that it will execute last and not close the
+	 * handles until all other atexit handlers have finished
+	 */
+	atexit(wait_for_pager_atexit);
 	trace_command_performance(argv);
+	atexit(post_command_hook_atexit);
 
 	/*
 	 * "git-xxxx" is the same as "git xxxx", but we obviously:
@@ -810,10 +921,14 @@ int cmd_main(int argc, const char **argv)
 	} else {
 		/* The user didn't specify a command; give them help */
 		commit_pager_choice();
+		if (run_pre_command_hook(argv))
+			die("pre-command hook aborted command");
 		printf("usage: %s\n\n", git_usage_string);
 		list_common_cmds_help();
 		printf("\n%s\n", _(git_more_info_string));
-		exit(1);
+		exit_code = 1;
+		run_post_command_hook();
+		exit(exit_code);
 	}
 	cmd = argv[0];
 
@@ -845,5 +960,5 @@ int cmd_main(int argc, const char **argv)
 	fprintf(stderr, _("failed to run command '%s': %s\n"),
 		cmd, strerror(errno));
 
-	return 1;
+	return trace2_cmd_exit(1);
 }
diff --git a/gvfs.c b/gvfs.c
new file mode 100644
index 00000000000000..7235199c04ac39
--- /dev/null
+++ b/gvfs.c
@@ -0,0 +1,38 @@
+#include "cache.h"
+#include "gvfs.h"
+#include "config.h"
+
+static int gvfs_config_loaded;
+static int core_gvfs_is_bool;
+
+static int early_core_gvfs_config(const char *var, const char *value, void *data)
+{
+	if (!strcmp(var, "core.gvfs"))
+		core_gvfs = git_config_bool_or_int("core.gvfs", value, &core_gvfs_is_bool);
+	return 0;
+}
+
+void gvfs_load_config_value(const char *value)
+{
+	if (gvfs_config_loaded)
+		return;
+
+	if (value)
+		core_gvfs = git_config_bool_or_int("core.gvfs", value, &core_gvfs_is_bool);
+	else if (startup_info->have_repository == 0)
+		read_early_config(early_core_gvfs_config, NULL);
+	else
+		git_config_get_bool_or_int("core.gvfs", &core_gvfs_is_bool, &core_gvfs);
+
+	/* Turn on all bits if a bool was set in the settings */
+	if (core_gvfs_is_bool && core_gvfs)
+		core_gvfs = -1;
+
+	gvfs_config_loaded = 1;
+}
+
+int gvfs_config_is_set(int mask)
+{
+	gvfs_load_config_value(0);
+	return (core_gvfs & mask) == mask;
+}
diff --git a/gvfs.h b/gvfs.h
new file mode 100644
index 00000000000000..7c9367866f502a
--- /dev/null
+++ b/gvfs.h
@@ -0,0 +1,23 @@
+#ifndef GVFS_H
+#define GVFS_H
+
+
+/*
+ * This file is for the specific settings and methods
+ * used for GVFS functionality
+ */
+
+
+/*
+ * The list of bits in the core_gvfs setting
+ */
+#define GVFS_SKIP_SHA_ON_INDEX                      (1 << 0)
+#define GVFS_MISSING_OK                             (1 << 2)
+#define GVFS_NO_DELETE_OUTSIDE_SPARSECHECKOUT       (1 << 3)
+#define GVFS_FETCH_SKIP_REACHABILITY_AND_UPLOADPACK (1 << 4)
+#define GVFS_BLOCK_FILTERS_AND_EOL_CONVERSIONS      (1 << 6)
+
+void gvfs_load_config_value(const char *value);
+int gvfs_config_is_set(int mask);
+
+#endif /* GVFS_H */
diff --git a/merge-recursive.c b/merge-recursive.c
index acc2f64a4e9d03..5938f4517ed72b 100644
--- a/merge-recursive.c
+++ b/merge-recursive.c
@@ -1509,7 +1509,7 @@ static int handle_change_delete(struct merge_options *o,
 		 * path.  We could call update_file_flags() with update_cache=0
 		 * and update_wd=0, but that's a no-op.
 		 */
-		if (change_branch != o->branch1 || alt_path)
+		if (change_branch != o->branch1 || alt_path || !file_exists(update_path))
 			ret = update_file(o, 0, changed_oid, changed_mode, update_path);
 	}
 	free(alt_path);
diff --git a/pager.c b/pager.c
index a768797fcfcc44..1c82a868ee0a7d 100644
--- a/pager.c
+++ b/pager.c
@@ -26,9 +26,12 @@ static void wait_for_pager(int in_signal)
 		finish_command(&pager_process);
 }
 
-static void wait_for_pager_atexit(void)
+
+static int run_wait_for_pager_atexit = 0;
+void wait_for_pager_atexit(void)
 {
-	wait_for_pager(0);
+	if (run_wait_for_pager_atexit)
+		wait_for_pager(0);
 }
 
 static void wait_for_pager_signal(int signo)
@@ -100,6 +103,7 @@ void prepare_pager_args(struct child_process *pager_process, const char *pager)
 	argv_array_push(&pager_process->args, pager);
 	pager_process->use_shell = 1;
 	setup_pager_env(&pager_process->env_array);
+	pager_process->trace2_child_class = "pager";
 }
 
 void setup_pager(void)
@@ -137,7 +141,7 @@ void setup_pager(void)
 
 	/* this makes sure that the parent terminates after the pager */
 	sigchain_push_common(wait_for_pager_signal);
-	atexit(wait_for_pager_atexit);
+	run_wait_for_pager_atexit = 1;
 }
 
 int pager_in_use(void)
diff --git a/pkt-line.c b/pkt-line.c
index 04d10bbd037b39..183a503a2a8d12 100644
--- a/pkt-line.c
+++ b/pkt-line.c
@@ -183,7 +183,7 @@ int packet_write_fmt_gently(int fd, const char *fmt, ...)
 	return status;
 }
 
-static int packet_write_gently(const int fd_out, const char *buf, size_t size)
+int packet_write_gently(const int fd_out, const char *buf, size_t size)
 {
 	static char packet_write_buffer[LARGE_PACKET_MAX];
 	size_t packet_size;
diff --git a/pkt-line.h b/pkt-line.h
index 5b28d43472db41..801799b369c78c 100644
--- a/pkt-line.h
+++ b/pkt-line.h
@@ -29,6 +29,7 @@ void packet_buf_write(struct strbuf *buf, const char *fmt, ...) __attribute__((f
 void packet_buf_write_len(struct strbuf *buf, const char *data, size_t len);
 int packet_flush_gently(int fd);
 int packet_write_fmt_gently(int fd, const char *fmt, ...) __attribute__((format (printf, 2, 3)));
+int packet_write_gently(const int fd_out, const char *buf, size_t size);
 int write_packetized_from_fd(int fd_in, int fd_out);
 int write_packetized_from_buf(const char *src_in, size_t len, int fd_out);
 
diff --git a/read-cache.c b/read-cache.c
index 49b6050342fbd4..df50a8b727c0a6 100644
--- a/read-cache.c
+++ b/read-cache.c
@@ -18,6 +18,7 @@
 #include "commit.h"
 #include "blob.h"
 #include "resolve-undo.h"
+#include "run-command.h"
 #include "strbuf.h"
 #include "varint.h"
 #include "split-index.h"
@@ -25,6 +26,8 @@
 #include "fsmonitor.h"
 #include "thread-utils.h"
 #include "progress.h"
+#include "virtualfilesystem.h"
+#include "gvfs.h"
 
 /* Mask for the name length in ce_flags in the on-disk index */
 
@@ -1896,6 +1899,7 @@ static void post_read_index_from(struct index_state *istate)
 	tweak_untracked_cache(istate);
 	tweak_split_index(istate);
 	tweak_fsmonitor(istate);
+	apply_virtualfilesystem(istate);
 }
 
 static size_t estimate_cache_size_from_compressed(unsigned int entries)
@@ -2233,6 +2237,14 @@ int do_read_index(struct index_state *istate, const char *path, int must_exist)
 		load_index_extensions(&p);
 	}
 	munmap((void *)mmap, mmap_size);
+
+	/*
+	 * TODO trace2: replace "the_repository" with the actual repo instance
+	 * that is associated with the given "istate".
+	 */
+	trace2_data_intmax("index", the_repository, "read/version", istate->version);
+	trace2_data_intmax("index", the_repository, "read/cache_nr", istate->cache_nr);
+
 	return istate->cache_nr;
 
 unmap:
@@ -2264,9 +2276,17 @@ int read_index_from(struct index_state *istate, const char *path,
 	if (istate->initialized)
 		return istate->cache_nr;
 
+	/*
+	 * TODO trace2: replace "the_repository" with the actual repo instance
+	 * that is associated with the given "istate".
+	 */
+	trace2_region_enter_printf("index", "do_read_index", the_repository,
+				   "%s", path);
 	trace_performance_enter();
 	ret = do_read_index(istate, path, 0);
 	trace_performance_leave("read cache %s", path);
+	trace2_region_leave_printf("index", "do_read_index", the_repository,
+				   "%s", path);
 
 	split_index = istate->split_index;
 	if (!split_index || is_null_oid(&split_index->base_oid)) {
@@ -2282,7 +2302,11 @@ int read_index_from(struct index_state *istate, const char *path,
 
 	base_oid_hex = oid_to_hex(&split_index->base_oid);
 	base_path = xstrfmt("%s/sharedindex.%s", gitdir, base_oid_hex);
+	trace2_region_enter_printf("index", "shared/do_read_index", the_repository,
+				   "%s", base_path);
 	ret = do_read_index(split_index->base, base_path, 1);
+	trace2_region_leave_printf("index", "shared/do_read_index", the_repository,
+				   "%s", base_path);
 	if (!oideq(&split_index->base_oid, &split_index->base->oid))
 		die("broken index, expect %s in %s, got %s",
 		    base_oid_hex, base_path,
@@ -2422,7 +2446,9 @@ static int ce_write_flush(git_hash_ctx *context, int fd)
 {
 	unsigned int buffered = write_buffer_len;
 	if (buffered) {
-		the_hash_algo->update_fn(context, write_buffer, buffered);
+		if (!gvfs_config_is_set(GVFS_SKIP_SHA_ON_INDEX))
+			the_hash_algo->update_fn(context, write_buffer,
+						 buffered);
 		if (write_in_full(fd, write_buffer, buffered) < 0)
 			return -1;
 		write_buffer_len = 0;
@@ -2471,7 +2497,8 @@ static int ce_flush(git_hash_ctx *context, int fd, unsigned char *hash)
 
 	if (left) {
 		write_buffer_len = 0;
-		the_hash_algo->update_fn(context, write_buffer, left);
+		if (!gvfs_config_is_set(GVFS_SKIP_SHA_ON_INDEX))
+			the_hash_algo->update_fn(context, write_buffer, left);
 	}
 
 	/* Flush first if not enough space for hash signature */
@@ -2482,7 +2509,8 @@ static int ce_flush(git_hash_ctx *context, int fd, unsigned char *hash)
 	}
 
 	/* Append the hash signature at the end */
-	the_hash_algo->final_fn(write_buffer + left, context);
+	if (!gvfs_config_is_set(GVFS_SKIP_SHA_ON_INDEX))
+		the_hash_algo->final_fn(write_buffer + left, context);
 	hashcpy(hash, write_buffer + left);
 	left += the_hash_algo->rawsz;
 	return (write_in_full(fd, write_buffer, left) < 0) ? -1 : 0;
@@ -2989,6 +3017,14 @@ static int do_write_index(struct index_state *istate, struct tempfile *tempfile,
 	istate->timestamp.sec = (unsigned int)st.st_mtime;
 	istate->timestamp.nsec = ST_MTIME_NSEC(st);
 	trace_performance_since(start, "write index, changed mask = %x", istate->cache_changed);
+
+	/*
+	 * TODO trace2: replace "the_repository" with the actual repo instance
+	 * that is associated with the given "istate".
+	 */
+	trace2_data_intmax("index", the_repository, "write/version", istate->version);
+	trace2_data_intmax("index", the_repository, "write/cache_nr", istate->cache_nr);
+
 	return 0;
 }
 
@@ -3008,12 +3044,32 @@ static int commit_locked_index(struct lock_file *lk)
 static int do_write_locked_index(struct index_state *istate, struct lock_file *lock,
 				 unsigned flags)
 {
-	int ret = do_write_index(istate, lock->tempfile, 0);
+	int ret;
+
+	/*
+	 * TODO trace2: replace "the_repository" with the actual repo instance
+	 * that is associated with the given "istate".
+	 */
+	trace2_region_enter_printf("index", "do_write_index", the_repository,
+				   "%s", lock->tempfile->filename.buf);
+	ret = do_write_index(istate, lock->tempfile, 0);
+	trace2_region_leave_printf("index", "do_write_index", the_repository,
+				   "%s", lock->tempfile->filename.buf);
+
 	if (ret)
 		return ret;
 	if (flags & COMMIT_LOCK)
-		return commit_locked_index(lock);
-	return close_lock_file_gently(lock);
+		ret = commit_locked_index(lock);
+	else
+		ret = close_lock_file_gently(lock);
+
+	run_hook_le(NULL, "post-indexchanged",
+			istate->updated_workdir ? "1" : "0",
+			istate->updated_skipworktree ? "1" : "0", NULL);
+	istate->updated_workdir = 0;
+	istate->updated_skipworktree = 0;
+
+	return ret;
 }
 
 static int write_split_index(struct index_state *istate,
@@ -3093,7 +3149,13 @@ static int write_shared_index(struct index_state *istate,
 	int ret;
 
 	move_cache_to_base_index(istate);
+
+	trace2_region_enter_printf("index", "shared/do_write_index",
+				   the_repository, "%s", (*temp)->filename.buf);
 	ret = do_write_index(si->base, *temp, 1);
+	trace2_region_enter_printf("index", "shared/do_write_index",
+				   the_repository, "%s", (*temp)->filename.buf);
+
 	if (ret)
 		return ret;
 	ret = adjust_shared_perm(get_tempfile_path(*temp));
diff --git a/remote-curl.c b/remote-curl.c
index 1220dffcdc57a1..8950b5c383f1b2 100644
--- a/remote-curl.c
+++ b/remote-curl.c
@@ -1340,6 +1340,13 @@ int cmd_main(int argc, const char **argv)
 	string_list_init(&options.deepen_not, 1);
 	string_list_init(&options.push_options, 1);
 
+	/*
+	 * Just report "remote-curl" here (folding all the various aliases
+	 * ("git-remote-http", "git-remote-https", and etc.) here since they
+	 * are all just copies of the same actual executable.
+	 */
+	trace2_cmd_verb("remote-curl");
+
 	remote = remote_get(argv[1]);
 
 	if (argc > 2) {
diff --git a/repository.c b/repository.c
index 5dd148671811b3..a84055ed1d9e3d 100644
--- a/repository.c
+++ b/repository.c
@@ -113,6 +113,8 @@ static int repo_init_gitdir(struct repository *repo, const char *gitdir)
 void repo_set_worktree(struct repository *repo, const char *path)
 {
 	repo->worktree = real_pathdup(path, 1);
+
+	trace2_def_repo(repo);
 }
 
 static int read_and_verify_repository_format(struct repository_format *format,
diff --git a/repository.h b/repository.h
index 9f16c42c1ed04a..97b03846ba544a 100644
--- a/repository.h
+++ b/repository.h
@@ -90,6 +90,9 @@ struct repository {
 	/* Repository's current hash algorithm, as serialized on disk. */
 	const struct git_hash_algo *hash_algo;
 
+	/* A unique-id for tracing purposes. */
+	int trace2_repo_id;
+
 	/* Configurations */
 
 	/* Indicate if a repository has a different 'commondir' from 'gitdir' */
diff --git a/run-command.c b/run-command.c
index c11ff8067481f7..ab4ab8cf8d2d03 100644
--- a/run-command.c
+++ b/run-command.c
@@ -7,6 +7,7 @@
 #include "strbuf.h"
 #include "string-list.h"
 #include "quote.h"
+#include "config.h"
 
 void child_process_init(struct child_process *child)
 {
@@ -712,6 +713,7 @@ int start_command(struct child_process *cmd)
 		cmd->err = fderr[0];
 	}
 
+	trace2_child_start(cmd);
 	trace_run_command(cmd);
 
 	fflush(NULL);
@@ -924,6 +926,8 @@ int start_command(struct child_process *cmd)
 #endif
 
 	if (cmd->pid < 0) {
+		trace2_child_exit(cmd, -1);
+
 		if (need_in)
 			close_pair(fdin);
 		else if (cmd->in)
@@ -962,13 +966,16 @@ int start_command(struct child_process *cmd)
 int finish_command(struct child_process *cmd)
 {
 	int ret = wait_or_whine(cmd->pid, cmd->argv[0], 0);
+	trace2_child_exit(cmd, ret);
 	child_process_clear(cmd);
 	return ret;
 }
 
 int finish_command_in_signal(struct child_process *cmd)
 {
-	return wait_or_whine(cmd->pid, cmd->argv[0], 1);
+	int ret = wait_or_whine(cmd->pid, cmd->argv[0], 1);
+	trace2_child_exit(cmd, ret);
+	return ret;
 }
 
 
@@ -990,7 +997,18 @@ int run_command_v_opt(const char **argv, int opt)
 	return run_command_v_opt_cd_env(argv, opt, NULL, NULL);
 }
 
+int run_command_v_opt_tr2(const char **argv, int opt, const char *tr2_class)
+{
+	return run_command_v_opt_cd_env_tr2(argv, opt, NULL, NULL, tr2_class);
+}
+
 int run_command_v_opt_cd_env(const char **argv, int opt, const char *dir, const char *const *env)
+{
+	return run_command_v_opt_cd_env_tr2(argv, opt, dir, env, NULL);
+}
+
+int run_command_v_opt_cd_env_tr2(const char **argv, int opt, const char *dir, const char *const *env,
+				 const char *tr2_class)
 {
 	struct child_process cmd = CHILD_PROCESS_INIT;
 	cmd.argv = argv;
@@ -1002,6 +1020,7 @@ int run_command_v_opt_cd_env(const char **argv, int opt, const char *dir, const
 	cmd.clean_on_exit = opt & RUN_CLEAN_ON_EXIT ? 1 : 0;
 	cmd.dir = dir;
 	cmd.env = env;
+	cmd.trace2_child_class = tr2_class;
 	return run_command(&cmd);
 }
 
@@ -1268,12 +1287,69 @@ int async_with_fork(void)
 #endif
 }
 
+static int early_hooks_path_config(const char *var, const char *value, void *data)
+{
+	if (!strcmp(var, "core.hookspath"))
+		return git_config_pathname((const char **)data, var, value);
+
+	return 0;
+}
+
+/* Discover the hook before setup_git_directory() was called */
+static const char *hook_path_early(const char *name, struct strbuf *result)
+{
+	static struct strbuf hooks_dir = STRBUF_INIT;
+	static int initialized;
+
+	if (initialized < 0)
+		return NULL;
+
+	if (!initialized) {
+		struct strbuf gitdir = STRBUF_INIT, commondir = STRBUF_INIT;
+		const char *early_hooks_dir = NULL;
+
+		if (discover_git_directory(&commondir, &gitdir) < 0) {
+			initialized = -1;
+			return NULL;
+		}
+
+		read_early_config(early_hooks_path_config, &early_hooks_dir);
+		if (!early_hooks_dir)
+			strbuf_addf(&hooks_dir, "%s/hooks/", commondir.buf);
+		else {
+			strbuf_add_absolute_path(&hooks_dir, early_hooks_dir);
+			strbuf_addch(&hooks_dir, '/');
+		}
+
+		strbuf_release(&gitdir);
+		strbuf_release(&commondir);
+
+		initialized = 1;
+	}
+
+	strbuf_addf(result, "%s%s", hooks_dir.buf, name);
+	return result->buf;
+}
+
 const char *find_hook(const char *name)
 {
 	static struct strbuf path = STRBUF_INIT;
 
 	strbuf_reset(&path);
-	strbuf_git_path(&path, "hooks/%s", name);
+	if (have_git_dir()) {
+		static int forced_config;
+
+		if (!forced_config) {
+			if (!git_hooks_path)
+				git_config_get_pathname("core.hookspath",
+							&git_hooks_path);
+			forced_config = 1;
+		}
+
+		strbuf_git_path(&path, "hooks/%s", name);
+	} else if (!hook_path_early(name, &path))
+		return NULL;
+
 	if (access(path.buf, X_OK) < 0) {
 		int err = errno;
 
@@ -1302,7 +1378,8 @@ const char *find_hook(const char *name)
 	return path.buf;
 }
 
-int run_hook_ve(const char *const *env, const char *name, va_list args)
+int run_hook_argv(const char *const *env, const char *name,
+		  const char **argv)
 {
 	struct child_process hook = CHILD_PROCESS_INIT;
 	const char *p;
@@ -1312,8 +1389,7 @@ int run_hook_ve(const char *const *env, const char *name, va_list args)
 		return 0;
 
 	argv_array_push(&hook.args, p);
-	while ((p = va_arg(args, const char *)))
-		argv_array_push(&hook.args, p);
+	argv_array_pushv(&hook.args, argv);
 	hook.env = env;
 	hook.no_stdin = 1;
 	hook.stdout_to_stderr = 1;
@@ -1321,6 +1397,20 @@ int run_hook_ve(const char *const *env, const char *name, va_list args)
 	return run_command(&hook);
 }
 
+int run_hook_ve(const char *const *env, const char *name, va_list args)
+{
+	struct argv_array argv = ARGV_ARRAY_INIT;
+	const char *p;
+	int ret;
+
+	while ((p = va_arg(args, const char *)))
+		argv_array_push(&argv, p);
+
+	ret = run_hook_argv(env, name, argv.argv);
+	argv_array_clear(&argv);
+	return ret;
+}
+
 int run_hook_le(const char *const *env, const char *name, ...)
 {
 	va_list args;
@@ -1774,6 +1864,15 @@ int run_processes_parallel(int n,
 	int output_timeout = 100;
 	int spawn_cap = 4;
 	struct parallel_processes pp;
+	/*
+	 * TODO Currently all callers of run_processes_parallel()
+	 * are in the submodule code, so hard-coding the category
+	 * is OK for now.  Later, pass in category to this function.
+	 */
+	const char *category = "submodule";
+
+	trace2_region_enter_printf(category, "run_pp", NULL,
+				   "max:%d", ((n < 1) ? online_cpus() : n));
 
 	pp_init(&pp, n, get_next_task, start_failure, task_finished, pp_cb);
 	while (1) {
@@ -1803,5 +1902,8 @@ int run_processes_parallel(int n,
 	}
 
 	pp_cleanup(&pp);
+
+	trace2_region_leave(category, "run_pp", NULL);
+
 	return 0;
 }
diff --git a/run-command.h b/run-command.h
index 68f5369fc2d432..36576d790fde68 100644
--- a/run-command.h
+++ b/run-command.h
@@ -10,6 +10,11 @@ struct child_process {
 	struct argv_array args;
 	struct argv_array env_array;
 	pid_t pid;
+
+	int trace2_child_id;
+	uint64_t trace2_child_us_start;
+	const char *trace2_child_class;
+
 	/*
 	 * Using .in, .out, .err:
 	 * - Specify 0 for no redirections (child inherits stdin, stdout,
@@ -65,6 +70,8 @@ extern const char *find_hook(const char *name);
 LAST_ARG_MUST_BE_NULL
 extern int run_hook_le(const char *const *env, const char *name, ...);
 extern int run_hook_ve(const char *const *env, const char *name, va_list args);
+extern int run_hook_argv(const char *const *env, const char *name,
+			 const char **argv);
 
 #define RUN_COMMAND_NO_STDIN 1
 #define RUN_GIT_CMD	     2	/*If this is to be git sub-command */
@@ -73,12 +80,15 @@ extern int run_hook_ve(const char *const *env, const char *name, va_list args);
 #define RUN_USING_SHELL 16
 #define RUN_CLEAN_ON_EXIT 32
 int run_command_v_opt(const char **argv, int opt);
-
+int run_command_v_opt_tr2(const char **argv, int opt, const char *tr2_class
+);
 /*
  * env (the environment) is to be formatted like environ: "VAR=VALUE".
  * To unset an environment variable use just "VAR".
  */
 int run_command_v_opt_cd_env(const char **argv, int opt, const char *dir, const char *const *env);
+int run_command_v_opt_cd_env_tr2(const char **argv, int opt, const char *dir, const char *const *env,
+				 const char *tr2_class);
 
 /**
  * Execute the given command, sending "in" to its stdin, and capturing its
diff --git a/send-pack.c b/send-pack.c
index 9ff928e2f77bf0..4cce09534509e6 100644
--- a/send-pack.c
+++ b/send-pack.c
@@ -15,6 +15,7 @@
 #include "sha1-array.h"
 #include "gpg-interface.h"
 #include "cache.h"
+#include "gvfs.h"
 
 int option_parse_push_signed(const struct option *opt,
 			     const char *arg, int unset)
@@ -50,7 +51,7 @@ static int send_pack_config(const char *var, const char *value, void *unused)
 
 static void feed_object(const struct object_id *oid, FILE *fh, int negative)
 {
-	if (negative && !has_sha1_file(oid->hash))
+	if (negative && !gvfs_config_is_set(GVFS_MISSING_OK) && !has_sha1_file(oid->hash))
 		return;
 
 	if (negative)
diff --git a/sh-i18n--envsubst.c b/sh-i18n--envsubst.c
index 09c6b445b96312..2296ba1a2d6361 100644
--- a/sh-i18n--envsubst.c
+++ b/sh-i18n--envsubst.c
@@ -14,6 +14,7 @@
  */
 
 #include "git-compat-util.h"
+#include "trace2.h"
 
 /* Substitution of environment variables in shell format strings.
    Copyright (C) 2003-2007 Free Software Foundation, Inc.
@@ -67,6 +68,8 @@ cmd_main (int argc, const char *argv[])
   /* Default values for command line options.  */
   /* unsigned short int show_variables = 0; */
 
+  trace2_cmd_verb("sh-i18n--envsubst");
+
   switch (argc)
 	{
 	case 1:
diff --git a/sha1-file.c b/sha1-file.c
index 5bd11c85bc5636..4f829e8c608db5 100644
--- a/sha1-file.c
+++ b/sha1-file.c
@@ -32,6 +32,9 @@
 #include "packfile.h"
 #include "fetch-object.h"
 #include "object-store.h"
+#include "sigchain.h"
+#include "sub-process.h"
+#include "pkt-line.h"
 
 /* The maximum size for an object header. */
 #define MAX_HEADER_LEN 32
@@ -707,6 +710,124 @@ void prepare_alt_odb(struct repository *r)
 	read_info_alternates(r, r->objects->objectdir, 0);
 }
 
+#define CAP_GET    (1u<<0)
+
+static int subprocess_map_initialized;
+static struct hashmap subprocess_map;
+
+struct read_object_process {
+	struct subprocess_entry subprocess;
+	unsigned int supported_capabilities;
+};
+
+static int start_read_object_fn(struct subprocess_entry *subprocess)
+{
+	struct read_object_process *entry = (struct read_object_process *)subprocess;
+	static int versions[] = {1, 0};
+	static struct subprocess_capability capabilities[] = {
+		{ "get", CAP_GET },
+		{ NULL, 0 }
+	};
+
+	return subprocess_handshake(subprocess, "git-read-object", versions,
+				    NULL, capabilities,
+				    &entry->supported_capabilities);
+}
+
+static int read_object_process(const struct object_id *oid)
+{
+	int err;
+	struct read_object_process *entry;
+	struct child_process *process;
+	struct strbuf status = STRBUF_INIT;
+	const char *cmd = find_hook("read-object");
+	uint64_t start;
+
+	start = getnanotime();
+
+	trace2_region_enter("subprocess", "read_object", the_repository);
+
+	if (!subprocess_map_initialized) {
+		subprocess_map_initialized = 1;
+		hashmap_init(&subprocess_map, (hashmap_cmp_fn)cmd2process_cmp,
+			     NULL, 0);
+		entry = NULL;
+	} else {
+		entry = (struct read_object_process *) subprocess_find_entry(&subprocess_map, cmd);
+	}
+
+	if (!entry) {
+		entry = xmalloc(sizeof(*entry));
+		entry->supported_capabilities = 0;
+
+		if (subprocess_start(&subprocess_map, &entry->subprocess, cmd,
+				     start_read_object_fn)) {
+			free(entry);
+			err = -1;
+			goto leave_region;
+		}
+	}
+	process = &entry->subprocess.process;
+
+	if (!(CAP_GET & entry->supported_capabilities)) {
+		err = -1;
+		goto leave_region;
+	}
+
+	sigchain_push(SIGPIPE, SIG_IGN);
+
+	err = packet_write_fmt_gently(process->in, "command=get\n");
+	if (err)
+		goto done;
+
+	err = packet_write_fmt_gently(process->in, "sha1=%s\n", oid_to_hex(oid));
+	if (err)
+		goto done;
+
+	err = packet_flush_gently(process->in);
+	if (err)
+		goto done;
+
+	err = subprocess_read_status(process->out, &status);
+	err = err ? err : strcmp(status.buf, "success");
+
+done:
+	sigchain_pop(SIGPIPE);
+
+	if (err || errno == EPIPE) {
+		err = err ? err : errno;
+		if (!strcmp(status.buf, "error")) {
+			/* The process signaled a problem with the file. */
+		}
+		else if (!strcmp(status.buf, "abort")) {
+			/*
+			 * The process signaled a permanent problem. Don't try to read
+			 * objects with the same command for the lifetime of the current
+			 * Git process.
+			 */
+			entry->supported_capabilities &= ~CAP_GET;
+		}
+		else {
+			/*
+			 * Something went wrong with the read-object process.
+			 * Force shutdown and restart if needed.
+			 */
+			error("external process '%s' failed", cmd);
+			subprocess_stop(&subprocess_map,
+					(struct subprocess_entry *)entry);
+			free(entry);
+		}
+	}
+
+	trace_performance_since(start, "read_object_process");
+
+leave_region:
+	trace2_region_leave_printf("subprocess", "read_object", the_repository,
+				   "result %d", err);
+
+	return err;
+}
+
 /* Returns 1 if we have successfully freshened the file, 0 otherwise. */
 static int freshen_file(const char *fn)
 {
@@ -753,10 +874,23 @@ static int check_and_freshen_nonlocal(const struct object_id *oid, int freshen)
 	return 0;
 }
 
-static int check_and_freshen(const struct object_id *oid, int freshen)
+static int check_and_freshen(const struct object_id *oid, int freshen,
+			     int skip_virtualized_objects)
 {
-	return check_and_freshen_local(oid, freshen) ||
+	int ret;
+	int tried_hook = 0;
+
+retry:
+	ret = check_and_freshen_local(oid, freshen) ||
 	       check_and_freshen_nonlocal(oid, freshen);
+	if (!ret && core_virtualize_objects && !skip_virtualized_objects &&
+	    !tried_hook) {
+		tried_hook = 1;
+		if (!read_object_process(oid))
+			goto retry;
+	}
+
+	return ret;
 }
 
 int has_loose_object_nonlocal(const struct object_id *oid)
@@ -766,7 +900,7 @@ int has_loose_object_nonlocal(const struct object_id *oid)
 
 static int has_loose_object(const struct object_id *oid)
 {
-	return check_and_freshen(oid, 0);
+	return check_and_freshen(oid, 0, 0);
 }
 
 static void mmap_limit_check(size_t length)
@@ -1260,6 +1394,7 @@ int oid_object_info_extended(struct repository *r, const struct object_id *oid,
 	int rtype;
 	const struct object_id *real = oid;
 	int already_retried = 0;
+	int tried_hook = 0;
 
 	if (flags & OBJECT_INFO_LOOKUP_REPLACE)
 		real = lookup_replace_object(r, oid);
@@ -1270,6 +1405,7 @@ int oid_object_info_extended(struct repository *r, const struct object_id *oid,
 	if (!oi)
 		oi = &blank_oi;
 
+retry:
 	if (!(flags & OBJECT_INFO_SKIP_CACHED)) {
 		struct cached_object *co = find_cached_object(real);
 		if (co) {
@@ -1306,6 +1442,11 @@ int oid_object_info_extended(struct repository *r, const struct object_id *oid,
 			reprepare_packed_git(r);
 			if (find_pack_entry(r, real, &e))
 				break;
+			if (core_virtualize_objects && !tried_hook) {
+				tried_hook = 1;
+				if (!read_object_process(oid))
+					goto retry;
+			}
 		}
 
 		/* Check if it is a missing object */
@@ -1688,9 +1829,10 @@ static int write_loose_object(const struct object_id *oid, char *hdr,
 	return finalize_object_file(tmp_file.buf, filename.buf);
 }
 
-static int freshen_loose_object(const struct object_id *oid)
+static int freshen_loose_object(const struct object_id *oid,
+				int skip_virtualized_objects)
 {
-	return check_and_freshen(oid, 1);
+	return check_and_freshen(oid, 1, skip_virtualized_objects);
 }
 
 static int freshen_packed_object(const struct object_id *oid)
@@ -1716,7 +1858,7 @@ int write_object_file(const void *buf, unsigned long len, const char *type,
 	 * it out into .git/objects/??/?{38} file.
 	 */
 	write_object_file_prepare(buf, len, type, oid, hdr, &hdrlen);
-	if (freshen_packed_object(oid) || freshen_loose_object(oid))
+	if (freshen_packed_object(oid) || freshen_loose_object(oid, 1))
 		return 0;
 	return write_loose_object(oid, hdr, hdrlen, buf, len, 0);
 }
@@ -1735,7 +1877,7 @@ int hash_object_file_literally(const void *buf, unsigned long len,
 
 	if (!(flags & HASH_WRITE_OBJECT))
 		goto cleanup;
-	if (freshen_packed_object(oid) || freshen_loose_object(oid))
+	if (freshen_packed_object(oid) || freshen_loose_object(oid, 1))
 		goto cleanup;
 	status = write_loose_object(oid, header, hdrlen, buf, len, 0);
 
diff --git a/sha1-name.c b/sha1-name.c
index cf0e8a3f85f6f0..f15acfd2f18a3d 100644
--- a/sha1-name.c
+++ b/sha1-name.c
@@ -1217,7 +1217,8 @@ static int get_oid_oneline(const char *prefix, struct object_id *oid,
 		struct commit *commit;
 		int matches;
 
-		commit = pop_most_recent_commit(&list, ONELINE_SEEN);
+		commit = pop_most_recent_commit(&list, ONELINE_SEEN,
+						GENERATION_NUMBER_ZERO);
 		if (!parse_object(the_repository, &commit->object.oid))
 			continue;
 		buf = get_commit_buffer(commit, NULL);
diff --git a/sub-process.c b/sub-process.c
index 8d2a1707cfe1a7..3f4af935557c5e 100644
--- a/sub-process.c
+++ b/sub-process.c
@@ -88,6 +88,7 @@ int subprocess_start(struct hashmap *hashmap, struct subprocess_entry *entry, co
 	process->out = -1;
 	process->clean_on_exit = 1;
 	process->clean_on_exit_handler = subprocess_exit_handler;
+	process->trace2_child_class = "subprocess";
 
 	err = start_command(process);
 	if (err) {
diff --git a/t/helper/test-tool.c b/t/helper/test-tool.c
index 52304d0748ce52..cfb46a720ea919 100644
--- a/t/helper/test-tool.c
+++ b/t/helper/test-tool.c
@@ -1,5 +1,6 @@
 #include "git-compat-util.h"
 #include "test-tool.h"
+#include "trace2.h"
 
 struct test_cmd {
 	const char *name;
@@ -80,6 +81,8 @@ int cmd_main(int argc, const char **argv)
 		if (!strcmp(cmds[i].name, argv[1])) {
 			argv++;
 			argc--;
+			trace2_cmd_verb(cmds[i].name);
+			trace2_cmd_list_config();
 			return cmds[i].fn(argc, argv);
 		}
 	}
diff --git a/t/t0000-basic.sh b/t/t0000-basic.sh
index 12cb2679a18230..eb768e5effdd2f 100755
--- a/t/t0000-basic.sh
+++ b/t/t0000-basic.sh
@@ -1099,6 +1099,11 @@ test_expect_success 'writing this tree with --missing-ok' '
 	git write-tree --missing-ok
 '
 
+test_expect_success 'writing this tree with missing ok config value' '
+	git config core.gvfs 4 &&
+	git write-tree
+'
+
 
 ################################################################
 test_expect_success 'git read-tree followed by write-tree should be idempotent' '
diff --git a/t/t0021-conversion.sh b/t/t0021-conversion.sh
index 518ea6be6fbebc..a200b357c35ea8 100755
--- a/t/t0021-conversion.sh
+++ b/t/t0021-conversion.sh
@@ -314,6 +314,44 @@ test_expect_success "filter: smudge empty file" '
 	test_cmp expected filtered-empty-in-repo
 '
 
+test_expect_success "filter: clean filters blocked when under GVFS" '
+	test_config filter.empty-in-repo.clean "cat >/dev/null" &&
+	test_config filter.empty-in-repo.smudge "echo smudged && cat" &&
+	test_config core.gvfs 64 &&
+
+	echo dead data walking >empty-in-repo &&
+	test_must_fail git add empty-in-repo
+'
+
+test_expect_success "filter: smudge filters blocked when under GVFS" '
+	test_config filter.empty-in-repo.clean "cat >/dev/null" &&
+	test_config filter.empty-in-repo.smudge "echo smudged && cat" &&
+	test_config core.gvfs 64 &&
+
+	test_must_fail git checkout
+'
+
+test_expect_success "ident blocked on add when under GVFS" '
+	test_config core.gvfs 64 &&
+	test_config core.autocrlf false &&
+
+	echo "*.i ident" >.gitattributes &&
+	echo "\$Id\$" > ident.i &&
+
+	test_must_fail git add ident.i
+'
+
+test_expect_success "ident blocked when under GVFS" '
+	git add ident.i &&
+
+	git commit -m "added ident.i" &&
+	test_config core.gvfs 64 &&
+	rm ident.i &&
+	git checkout -- ident.i &&
+
+	test_must_fail git status
+'
+
 test_expect_success 'disable filter with empty override' '
 	test_config_global filter.disable.smudge false &&
 	test_config_global filter.disable.clean false &&
diff --git a/t/t0027-auto-crlf.sh b/t/t0027-auto-crlf.sh
index beb5927f77f7f2..b2fdc0e88be88c 100755
--- a/t/t0027-auto-crlf.sh
+++ b/t/t0027-auto-crlf.sh
@@ -331,6 +331,18 @@ checkout_files () {
 	"
 }
 
+test_expect_success 'crlf conversions blocked when under GVFS' '
+	git checkout -b gvfs &&
+	test_commit initial &&
+	rm initial.t &&
+	test_config core.gvfs 64 &&
+	test_config core.autocrlf true &&
+	test_must_fail git read-tree --reset -u HEAD &&
+
+	git config core.autocrlf false &&
+	git read-tree --reset -u HEAD
+'
+
 # Test control characters
 # NUL SOH CR EOF==^Z
 test_expect_success 'ls-files --eol -o Text/Binary' '
diff --git a/t/t0400-pre-command-hook.sh b/t/t0400-pre-command-hook.sh
new file mode 100755
index 00000000000000..2ab9833af5cce1
--- /dev/null
+++ b/t/t0400-pre-command-hook.sh
@@ -0,0 +1,69 @@
+#!/bin/sh
+
+test_description='pre-command hook'
+
+. ./test-lib.sh
+
+test_expect_success 'with no hook' '
+	echo "first" > file &&
+	git add file &&
+	git commit -m "first"
+'
+
+test_expect_success 'with succeeding hook' '
+	mkdir -p .git/hooks &&
+	write_script .git/hooks/pre-command <<-EOF &&
+	echo "\$*" | sed "s/ --git-pid=[0-9]*//" \
+		>\$(git rev-parse --git-dir)/pre-command.out
+	EOF
+	echo "second" >> file &&
+	git add file &&
+	test "add file" = "$(cat .git/pre-command.out)" &&
+	echo Hello | git hash-object --stdin &&
+	test "hash-object --stdin" = "$(cat .git/pre-command.out)"
+'
+
+test_expect_success 'with failing hook' '
+	write_script .git/hooks/pre-command <<-EOF &&
+	exit 1
+	EOF
+	echo "third" >> file &&
+	test_must_fail git add file &&
+	test_path_is_missing "$(cat .git/pre-command.out)"
+'
+
+test_expect_success 'in a subdirectory' '
+	echo touch i-was-here | write_script .git/hooks/pre-command &&
+	mkdir sub &&
+	(
+		cd sub &&
+		git version
+	) &&
+	test_path_is_file sub/i-was-here
+'
+
+test_expect_success 'in a subdirectory, using an alias' '
+	git reset --hard &&
+	echo "echo \"\$@; \$(pwd)\" >>log" |
+	write_script .git/hooks/pre-command &&
+	mkdir -p sub &&
+	(
+		cd sub &&
+		git -c alias.r="rebase HEAD" r
+	) &&
+	test_path_is_missing log &&
+	test_line_count = 2 sub/log
+'
+
+test_expect_success 'with core.hooksPath' '
+	mkdir -p .git/alternateHooks &&
+	write_script .git/alternateHooks/pre-command <<-EOF &&
+	echo "alternate" >\$(git rev-parse --git-dir)/pre-command.out
+	EOF
+	write_script .git/hooks/pre-command <<-EOF &&
+	echo "original"	>\$(git rev-parse --git-dir)/pre-command.out
+	EOF
+	git -c core.hooksPath=.git/alternateHooks status &&
+	test "alternate" = "$(cat .git/pre-command.out)"
+'
+test_done
diff --git a/t/t0401-post-command-hook.sh b/t/t0401-post-command-hook.sh
new file mode 100755
index 00000000000000..fcbfc4a0c79c1e
--- /dev/null
+++ b/t/t0401-post-command-hook.sh
@@ -0,0 +1,33 @@
+#!/bin/sh
+
+test_description='post-command hook'
+
+. ./test-lib.sh
+
+test_expect_success 'with no hook' '
+	echo "first" > file &&
+	git add file &&
+	git commit -m "first"
+'
+
+test_expect_success 'with succeeding hook' '
+	mkdir -p .git/hooks &&
+	write_script .git/hooks/post-command <<-EOF &&
+	echo "\$*" | sed "s/ --git-pid=[0-9]*//" \
+		>\$(git rev-parse --git-dir)/post-command.out
+	EOF
+	echo "second" >> file &&
+	git add file &&
+	test "add file --exit_code=0" = "$(cat .git/post-command.out)"
+'
+
+test_expect_success 'with failing pre-command hook' '
+	write_script .git/hooks/pre-command <<-EOF &&
+	exit 1
+	EOF
+	echo "third" >> file &&
+	test_must_fail git add file &&
+	test_path_is_missing "$(cat .git/post-command.out)"
+'
+
+test_done
diff --git a/t/t0410/read-object b/t/t0410/read-object
new file mode 100755
index 00000000000000..2360d4916ee81c
--- /dev/null
+++ b/t/t0410/read-object
@@ -0,0 +1,118 @@
+#!/usr/bin/perl
+#
+# Example implementation for the Git read-object protocol version 1
+# See Documentation/technical/read-object-protocol.txt
+#
+# Allows you to test the ability for blobs to be pulled from a host git repo
+# "on demand."  Called when git needs a blob it couldn't find locally due to
+# a lazy clone that only cloned the commits and trees.
+#
+# A lazy clone can be simulated via the following commands from the host repo
+# you wish to create a lazy clone of:
+#
+# cd /host_repo
+# git rev-parse HEAD
+# git init /guest_repo
+# git cat-file --batch-check --batch-all-objects | grep -v 'blob' |
+#	cut -d' ' -f1 | git pack-objects /guest_repo/.git/objects/pack/noblobs
+# cd /guest_repo
+# git config core.virtualizeobjects true
+# git reset --hard <sha from rev-parse call above>
+#
+# Please note, this sample is a minimal skeleton. No proper error handling
+# was implemented.
+#
+
+use strict;
+use warnings;
+
+#
+# Point $DIR to the folder where your host git repo is located so we can pull
+# missing objects from it
+#
+my $DIR = "../.git/";
+
+sub packet_bin_read {
+	my $buffer;
+	my $bytes_read = read STDIN, $buffer, 4;
+	if ( $bytes_read == 0 ) {
+
+		# EOF - Git stopped talking to us!
+		exit();
+	}
+	elsif ( $bytes_read != 4 ) {
+		die "invalid packet: '$buffer'";
+	}
+	my $pkt_size = hex($buffer);
+	if ( $pkt_size == 0 ) {
+		return ( 1, "" );
+	}
+	elsif ( $pkt_size > 4 ) {
+		my $content_size = $pkt_size - 4;
+		$bytes_read = read STDIN, $buffer, $content_size;
+		if ( $bytes_read != $content_size ) {
+			die "invalid packet ($content_size bytes expected; $bytes_read bytes read)";
+		}
+		return ( 0, $buffer );
+	}
+	else {
+		die "invalid packet size: $pkt_size";
+	}
+}
+
+sub packet_txt_read {
+	my ( $res, $buf ) = packet_bin_read();
+	unless ( $buf =~ s/\n$// ) {
+		die "A non-binary line MUST be terminated by an LF.";
+	}
+	return ( $res, $buf );
+}
+
+sub packet_bin_write {
+	my $buf = shift;
+	print STDOUT sprintf( "%04x", length($buf) + 4 );
+	print STDOUT $buf;
+	STDOUT->flush();
+}
+
+sub packet_txt_write {
+	packet_bin_write( $_[0] . "\n" );
+}
+
+sub packet_flush {
+	print STDOUT sprintf( "%04x", 0 );
+	STDOUT->flush();
+}
+
+( packet_txt_read() eq ( 0, "git-read-object-client" ) ) || die "bad initialize";
+( packet_txt_read() eq ( 0, "version=1" ) )				 || die "bad version";
+( packet_bin_read() eq ( 1, "" ) )                       || die "bad version end";
+
+packet_txt_write("git-read-object-server");
+packet_txt_write("version=1");
+packet_flush();
+
+( packet_txt_read() eq ( 0, "capability=get" ) )    || die "bad capability";
+( packet_bin_read() eq ( 1, "" ) )                  || die "bad capability end";
+
+packet_txt_write("capability=get");
+packet_flush();
+
+while (1) {
+	my ($command) = packet_txt_read() =~ /^command=([^=]+)$/;
+
+	if ( $command eq "get" ) {
+		my ($sha1) = packet_txt_read() =~ /^sha1=([0-9a-f]{40})$/;
+		packet_bin_read();
+
+		system ('git --git-dir="' . $DIR . '" cat-file blob ' . $sha1 . ' | git -c core.virtualizeobjects=false hash-object -w --stdin >/dev/null 2>&1');
+		packet_txt_write(($?) ? "status=error" : "status=success");
+		packet_flush();
+
+		open my $log, '>>.git/read-object-hook.log';
+		print $log "Read object $sha1, exit code $?\n";
+		close $log;
+	} else {
+		die "bad command '$command'";
+	}
+}
diff --git a/t/t0411-read-object.sh b/t/t0411-read-object.sh
new file mode 100755
index 00000000000000..af97ec5b50f356
--- /dev/null
+++ b/t/t0411-read-object.sh
@@ -0,0 +1,34 @@
+#!/bin/sh
+
+test_description='tests for long running read-object process'
+
+. ./test-lib.sh
+
+test_expect_success 'setup host repo with a root commit' '
+	test_commit zero &&
+	hash1=$(git ls-tree HEAD | grep zero.t | cut -f1 | cut -d\  -f3)
+'
+
+test_expect_success 'blobs can be retrieved from the host repo' '
+	git init guest-repo &&
+	(cd guest-repo &&
+	 mkdir -p .git/hooks &&
+	 cp $TEST_DIRECTORY/t0410/read-object .git/hooks/ &&
+	 git config core.virtualizeobjects true &&
+	 git cat-file blob "$hash1")
+'
+
+test_expect_success 'invalid blobs generate errors' '
+	(cd guest-repo &&
+	 test_must_fail git cat-file blob "invalid")
+'
+
+test_expect_success 'read-object-hook is bypassed when writing objects' '
+	(cd guest-repo &&
+	 echo hello >hello.txt &&
+	 git add hello.txt &&
+	 hash="$(git rev-parse --verify :hello.txt)" &&
+	 ! grep "$hash" .git/read-object-hook.log)
+'
+
+test_done
diff --git a/t/t1016-read-tree-skip-sha-on-read.sh b/t/t1016-read-tree-skip-sha-on-read.sh
new file mode 100755
index 00000000000000..5b76a80a0020dc
--- /dev/null
+++ b/t/t1016-read-tree-skip-sha-on-read.sh
@@ -0,0 +1,22 @@
+#!/bin/sh
+
+test_description='check that read-tree works with core.gvfs config value'
+
+. ./test-lib.sh
+. "$TEST_DIRECTORY"/lib-read-tree.sh
+
+test_expect_success setup '
+	echo one >a &&
+	git add a &&
+	git commit -m initial
+'
+test_expect_success 'read-tree without core.gvsf' '
+	read_tree_u_must_succeed -m -u HEAD
+'
+
+test_expect_success 'read-tree with core.gvfs set to 1' '
+	git config core.gvfs 1 &&
+	read_tree_u_must_succeed -m -u HEAD
+'
+
+test_done
diff --git a/t/t1090-sparse-checkout-scope.sh b/t/t1090-sparse-checkout-scope.sh
index 6e61b17c84d3e8..62735a6113c980 100755
--- a/t/t1090-sparse-checkout-scope.sh
+++ b/t/t1090-sparse-checkout-scope.sh
@@ -96,6 +96,23 @@ test_expect_success 'in partial clone, sparse checkout only fetches needed blobs
 	test_cmp expect actual
 '
 
+test_expect_success 'checkout does not delete items outside the sparse checkout file' '
+	git checkout master &&
+	git config core.gvfs 8 &&
+	git checkout -b outside &&
+	echo "new file1" >d &&
+	git add d &&
+	git commit -m "branch initial" &&
+	echo "new file1" >e &&
+	git add e &&
+	git commit -m "skipped worktree" &&
+	git update-index --skip-worktree e &&
+	echo "/d" >.git/info/sparse-checkout &&
+	git checkout HEAD^ &&
+	test_path_is_file d &&
+	test_path_is_file e
+'
+
 test_expect_success MINGW 'no unnecessary opendir() with fscache' '
 	git clone . fscache-test &&
 	(
diff --git a/t/t1092-virtualfilesystem.sh b/t/t1092-virtualfilesystem.sh
new file mode 100755
index 00000000000000..2379bca25a6426
--- /dev/null
+++ b/t/t1092-virtualfilesystem.sh
@@ -0,0 +1,370 @@
+#!/bin/sh
+
+test_description='virtual file system tests'
+
+. ./test-lib.sh
+
+clean_repo () {
+	rm .git/index &&
+	git -c core.virtualfilesystem= reset --hard HEAD &&
+	git -c core.virtualfilesystem= clean -fd &&
+	touch untracked.txt &&
+	touch dir1/untracked.txt &&
+	touch dir2/untracked.txt
+}
+
+test_expect_success 'setup' '
+	mkdir -p .git/hooks/ &&
+	cat > .gitignore <<-\EOF &&
+		.gitignore
+		expect*
+		actual*
+	EOF
+	mkdir -p dir1 &&
+	touch dir1/file1.txt &&
+	touch dir1/file2.txt &&
+	mkdir -p dir2 &&
+	touch dir2/file1.txt &&
+	touch dir2/file2.txt &&
+	git add . &&
+	git commit -m "initial" &&
+	git config --local core.virtualfilesystem .git/hooks/virtualfilesystem
+'
+
+test_expect_success 'test hook parameters and version' '
+	clean_repo &&
+	write_script .git/hooks/virtualfilesystem <<-\EOF &&
+		if test "$#" -ne 1
+		then
+			echo "$0: Exactly 1 argument expected" >&2
+			exit 2
+		fi
+
+		if test "$1" != 1
+		then
+			echo "$0: Unsupported hook version." >&2
+			exit 1
+		fi
+	EOF
+	git status &&
+	write_script .git/hooks/virtualfilesystem <<-\EOF &&
+		exit 3
+	EOF
+	test_must_fail git status
+'
+
+test_expect_success 'verify status is clean' '
+	clean_repo &&
+	write_script .git/hooks/virtualfilesystem <<-\EOF &&
+		printf "dir2/file1.txt\0"
+	EOF
+	rm -f .git/index &&
+	git checkout -f &&
+	write_script .git/hooks/virtualfilesystem <<-\EOF &&
+		printf "dir2/file1.txt\0"
+		printf "dir1/file1.txt\0"
+		printf "dir1/file2.txt\0"
+	EOF
+	git status > actual &&
+	cat > expected <<-\EOF &&
+		On branch master
+		nothing to commit, working tree clean
+	EOF
+	test_cmp expected actual
+'
+
+test_expect_success 'verify skip-worktree bit is set for absolute path' '
+	clean_repo &&
+	write_script .git/hooks/virtualfilesystem <<-\EOF &&
+		printf "dir1/file1.txt\0"
+	EOF
+	git ls-files -v > actual &&
+	cat > expected <<-\EOF &&
+		H dir1/file1.txt
+		S dir1/file2.txt
+		S dir2/file1.txt
+		S dir2/file2.txt
+	EOF
+	test_cmp expected actual
+'
+
+test_expect_success 'verify skip-worktree bit is cleared for absolute path' '
+	clean_repo &&
+	write_script .git/hooks/virtualfilesystem <<-\EOF &&
+		printf "dir1/file2.txt\0"
+	EOF
+	git ls-files -v > actual &&
+	cat > expected <<-\EOF &&
+		S dir1/file1.txt
+		H dir1/file2.txt
+		S dir2/file1.txt
+		S dir2/file2.txt
+	EOF
+	test_cmp expected actual
+'
+
+test_expect_success 'verify folder wild cards' '
+	clean_repo &&
+	write_script .git/hooks/virtualfilesystem <<-\EOF &&
+		printf "dir1/\0"
+	EOF
+	git ls-files -v > actual &&
+	cat > expected <<-\EOF &&
+		H dir1/file1.txt
+		H dir1/file2.txt
+		S dir2/file1.txt
+		S dir2/file2.txt
+	EOF
+	test_cmp expected actual
+'
+
+test_expect_success 'verify folders not included are ignored' '
+	clean_repo &&
+	write_script .git/hooks/virtualfilesystem <<-\EOF &&
+		printf "dir1/file1.txt\0"
+		printf "dir1/file2.txt\0"
+	EOF
+	mkdir -p dir1/dir2 &&
+	touch dir1/a &&
+	touch dir1/b &&
+	touch dir1/dir2/a &&
+	touch dir1/dir2/b &&
+	git add . &&
+	git ls-files -v > actual &&
+	cat > expected <<-\EOF &&
+		H dir1/file1.txt
+		H dir1/file2.txt
+		S dir2/file1.txt
+		S dir2/file2.txt
+	EOF
+	test_cmp expected actual
+'
+
+test_expect_success 'verify including one file doesnt include the rest' '
+	clean_repo &&
+	write_script .git/hooks/virtualfilesystem <<-\EOF &&
+		printf "dir1/file1.txt\0"
+		printf "dir1/file2.txt\0"
+		printf "dir1/dir2/a\0"
+	EOF
+	mkdir -p dir1/dir2 &&
+	touch dir1/a &&
+	touch dir1/b &&
+	touch dir1/dir2/a &&
+	touch dir1/dir2/b &&
+	git add . &&
+	git ls-files -v > actual &&
+	cat > expected <<-\EOF &&
+		H dir1/dir2/a
+		H dir1/file1.txt
+		H dir1/file2.txt
+		S dir2/file1.txt
+		S dir2/file2.txt
+	EOF
+	test_cmp expected actual
+'
+
+test_expect_success 'verify files not listed are ignored by git clean -f -x' '
+	clean_repo &&
+	write_script .git/hooks/virtualfilesystem <<-\EOF &&
+		printf "untracked.txt\0"
+		printf "dir1/\0"
+	EOF
+	mkdir -p dir3 &&
+	touch dir3/untracked.txt &&
+	git clean -f -x &&
+	test ! -f untracked.txt &&
+	test -d dir1 &&
+	test -f dir1/file1.txt &&
+	test -f dir1/file2.txt &&
+	test ! -f dir1/untracked.txt &&
+	test -f dir2/file1.txt &&
+	test -f dir2/file2.txt &&
+	test -f dir2/untracked.txt &&
+	test -d dir3 &&
+	test -f dir3/untracked.txt
+'
+
+test_expect_success 'verify files not listed are ignored by git clean -f -d -x' '
+	clean_repo &&
+	write_script .git/hooks/virtualfilesystem <<-\EOF &&
+		printf "untracked.txt\0"
+		printf "dir1/\0"
+		printf "dir3/\0"
+	EOF
+	mkdir -p dir3 &&
+	touch dir3/untracked.txt &&
+	git clean -f -d -x &&
+	test ! -f untracked.txt &&
+	test -d dir1 &&
+	test -f dir1/file1.txt &&
+	test -f dir1/file2.txt &&
+	test ! -f dir1/untracked.txt &&
+	test -f dir2/file1.txt &&
+	test -f dir2/file2.txt &&
+	test -f dir2/untracked.txt &&
+	test ! -d dir3 &&
+	test ! -f dir3/untracked.txt
+'
+
+test_expect_success 'verify folder entries include all files' '
+	clean_repo &&
+	write_script .git/hooks/virtualfilesystem <<-\EOF &&
+		printf "dir1/\0"
+	EOF
+	mkdir -p dir1/dir2 &&
+	touch dir1/a &&
+	touch dir1/b &&
+	touch dir1/dir2/a &&
+	touch dir1/dir2/b &&
+	git status -su > actual &&
+	cat > expected <<-\EOF &&
+		?? dir1/a
+		?? dir1/b
+		?? dir1/dir2/a
+		?? dir1/dir2/b
+		?? dir1/untracked.txt
+	EOF
+	test_cmp expected actual
+'
+
+test_expect_success 'verify case insensitivity of virtual file system entries' '
+	clean_repo &&
+	write_script .git/hooks/virtualfilesystem <<-\EOF &&
+		printf "dir1/a\0"
+		printf "Dir1/Dir2/a\0"
+		printf "DIR2/\0"
+	EOF
+	mkdir -p dir1/dir2 &&
+	touch dir1/a &&
+	touch dir1/b &&
+	touch dir1/dir2/a &&
+	touch dir1/dir2/b &&
+	git -c core.ignorecase=false status -su > actual &&
+	cat > expected <<-\EOF &&
+		?? dir1/a
+	EOF
+	test_cmp expected actual &&
+	git -c core.ignorecase=true status -su > actual &&
+	cat > expected <<-\EOF &&
+		?? dir1/a
+		?? dir1/dir2/a
+		?? dir2/untracked.txt
+	EOF
+	test_cmp expected actual
+'
+
+test_expect_success 'on file created' '
+	clean_repo &&
+	write_script .git/hooks/virtualfilesystem <<-\EOF &&
+		printf "dir1/file3.txt\0"
+	EOF
+	touch dir1/file3.txt &&
+	git add . &&
+	git ls-files -v > actual &&
+	cat > expected <<-\EOF &&
+		S dir1/file1.txt
+		S dir1/file2.txt
+		H dir1/file3.txt
+		S dir2/file1.txt
+		S dir2/file2.txt
+	EOF
+	test_cmp expected actual
+'
+
+test_expect_success 'on file renamed' '
+	clean_repo &&
+	write_script .git/hooks/virtualfilesystem <<-\EOF &&
+		printf "dir1/file1.txt\0"
+		printf "dir1/file3.txt\0"
+	EOF
+	mv dir1/file1.txt dir1/file3.txt &&
+	git status -su > actual &&
+	cat > expected <<-\EOF &&
+		 D dir1/file1.txt
+		?? dir1/file3.txt
+	EOF
+	test_cmp expected actual
+'
+
+test_expect_success 'on file deleted' '
+	clean_repo &&
+	write_script .git/hooks/virtualfilesystem <<-\EOF &&
+		printf "dir1/file1.txt\0"
+	EOF
+	rm dir1/file1.txt &&
+	git status -su > actual &&
+	cat > expected <<-\EOF &&
+		 D dir1/file1.txt
+	EOF
+	test_cmp expected actual
+'
+
+test_expect_success 'on file overwritten' '
+	clean_repo &&
+	write_script .git/hooks/virtualfilesystem <<-\EOF &&
+		printf "dir1/file1.txt\0"
+	EOF
+	echo "overwritten" > dir1/file1.txt &&
+	git status -su > actual &&
+	cat > expected <<-\EOF &&
+		 M dir1/file1.txt
+	EOF
+	test_cmp expected actual
+'
+
+test_expect_success 'on folder created' '
+	clean_repo &&
+	write_script .git/hooks/virtualfilesystem <<-\EOF &&
+		printf "dir1/dir1/\0"
+	EOF
+	mkdir -p dir1/dir1 &&
+	git status -su > actual &&
+	cat > expected <<-\EOF &&
+	EOF
+	test_cmp expected actual &&
+	git clean -fd &&
+	test ! -d "/dir1/dir1"
+'
+
+test_expect_success 'on folder renamed' '
+	clean_repo &&
+	write_script .git/hooks/virtualfilesystem <<-\EOF &&
+		printf "dir3/\0"
+		printf "dir1/file1.txt\0"
+		printf "dir1/file2.txt\0"
+		printf "dir3/file1.txt\0"
+		printf "dir3/file2.txt\0"
+	EOF
+	mv dir1 dir3 &&
+	git status -su > actual &&
+	cat > expected <<-\EOF &&
+		 D dir1/file1.txt
+		 D dir1/file2.txt
+		?? dir3/file1.txt
+		?? dir3/file2.txt
+		?? dir3/untracked.txt
+	EOF
+	test_cmp expected actual
+'
+
+test_expect_success 'folder with same prefix as file' '
+	clean_repo &&
+	touch dir1.sln &&
+	write_script .git/hooks/virtualfilesystem <<-\EOF &&
+		printf "dir1/\0"
+		printf "dir1.sln\0"
+	EOF
+	git add dir1.sln &&
+	git ls-files -v > actual &&
+	cat > expected <<-\EOF &&
+		H dir1.sln
+		H dir1/file1.txt
+		H dir1/file2.txt
+		S dir2/file1.txt
+		S dir2/file2.txt
+	EOF
+	test_cmp expected actual
+'
+
+test_done
diff --git a/t/t5581-gvfs.sh b/t/t5581-gvfs.sh
new file mode 100755
index 00000000000000..8a703cbb640387
--- /dev/null
+++ b/t/t5581-gvfs.sh
@@ -0,0 +1,24 @@
+#!/bin/sh
+
+test_description='fetch using the flag to skip reachability and upload pack'
+
+. ./test-lib.sh
+
+
+test_expect_success setup '
+	echo inital >a &&
+	git add a &&
+	git commit -m initial &&
+	git clone . one
+'
+
+test_expect_success "fetch test" '
+	cd one &&
+	git config core.gvfs 16 &&
+	rm -rf .git/objects/* &&
+	git -C .. cat-file commit HEAD | git hash-object -w --stdin -t commit &&
+	git fetch &&
+	test_must_fail git rev-parse --verify HEAD^{tree}
+'
+
+test_done
\ No newline at end of file
diff --git a/t/t6040-tracking-info.sh b/t/t6040-tracking-info.sh
index 716283b274677d..febf63f28a54cd 100755
--- a/t/t6040-tracking-info.sh
+++ b/t/t6040-tracking-info.sh
@@ -159,6 +159,19 @@ test_expect_success 'status -s -b --no-ahead-behind (diverged from upstream)' '
 	test_i18ncmp expect actual
 '
 
+cat >expect <<\EOF
+## b1...origin/master [different]
+EOF
+
+test_expect_success 'status.aheadbehind=false status -s -b (diverged from upstream)' '
+	(
+		cd test &&
+		git checkout b1 >/dev/null &&
+		git -c status.aheadbehind=false status -s -b | head -1
+	) >actual &&
+	test_i18ncmp expect actual
+'
+
 cat >expect <<\EOF
 On branch b1
 Your branch and 'origin/master' have diverged,
@@ -174,6 +187,15 @@ test_expect_success 'status --long --branch' '
 	test_i18ncmp expect actual
 '
 
+test_expect_success 'status --long --branch' '
+	(
+		cd test &&
+		git checkout b1 >/dev/null &&
+		git -c status.aheadbehind=true status --long -b | head -3
+	) >actual &&
+	test_i18ncmp expect actual
+'
+
 cat >expect <<\EOF
 On branch b1
 Your branch and 'origin/master' refer to different commits.
@@ -188,6 +210,15 @@ test_expect_success 'status --long --branch --no-ahead-behind' '
 	test_i18ncmp expect actual
 '
 
+test_expect_success 'status.aheadbehind=false status --long --branch' '
+	(
+		cd test &&
+		git checkout b1 >/dev/null &&
+		git -c status.aheadbehind=false status --long -b | head -2
+	) >actual &&
+	test_i18ncmp expect actual
+'
+
 cat >expect <<\EOF
 ## b5...brokenbase [gone]
 EOF
diff --git a/t/t7064-wtstatus-pv2.sh b/t/t7064-wtstatus-pv2.sh
index 11eccc231a792b..537787e598b414 100755
--- a/t/t7064-wtstatus-pv2.sh
+++ b/t/t7064-wtstatus-pv2.sh
@@ -445,6 +445,14 @@ test_expect_success 'verify --[no-]ahead-behind with V2 format' '
 		EOF
 
 		git status --ahead-behind --porcelain=v2 --branch --untracked-files=all >actual &&
+		test_cmp expect actual &&
+
+		# Confirm that "status.aheadbehind" DOES NOT work on V2 format.
+		git -c status.aheadbehind=false status --porcelain=v2 --branch --untracked-files=all >actual &&
+		test_cmp expect actual &&
+
+		# Confirm that "status.aheadbehind" DOES NOT work on V2 format.
+		git -c status.aheadbehind=true status --porcelain=v2 --branch --untracked-files=all >actual &&
 		test_cmp expect actual
 	)
 '
diff --git a/t/t7108-reset-stdin.sh b/t/t7108-reset-stdin.sh
index b7cbcbf869296c..db5483b8f10052 100755
--- a/t/t7108-reset-stdin.sh
+++ b/t/t7108-reset-stdin.sh
@@ -29,4 +29,13 @@ test_expect_success '--stdin requires --mixed' '
 	git reset --mixed --stdin <list
 '
 
+
+test_expect_success '--stdin trims carriage returns' '
+	test_commit endline &&
+	git rm endline.t &&
+	printf "endline.t\r\n" >list &&
+	git reset --stdin <list &&
+	test endline.t = "$(git ls-files endline.t)"
+'
+
 test_done
diff --git a/t/t7113-post-index-changed-hook.sh b/t/t7113-post-index-changed-hook.sh
new file mode 100755
index 00000000000000..71e3b2859109c8
--- /dev/null
+++ b/t/t7113-post-index-changed-hook.sh
@@ -0,0 +1,144 @@
+#!/bin/sh
+
+test_description='post index changed hook'
+
+. ./test-lib.sh
+
+test_expect_success 'setup' '
+	mkdir -p dir1 &&
+	touch dir1/file1.txt &&
+	echo testing >dir1/file2.txt &&
+	git add . &&
+	git commit -m "initial"
+'
+
+test_expect_success 'test status, add, commit, others trigger hook without flags set' '
+	mkdir -p .git/hooks &&
+	write_script .git/hooks/post-indexchanged <<-\EOF &&
+		if test "$1" -eq 1; then
+			echo "Invalid combination of flags passed to hook; updated_workdir is set." >testfailure
+			exit 1
+		fi
+		if test "$2" -eq 1; then
+			echo "Invalid combination of flags passed to hook; updated_skipworktree is set." >testfailure
+			exit 1
+		fi
+		if test -f ".git/index.lock"; then
+			echo ".git/index.lock exists" >testfailure
+			exit 3
+		fi
+		if ! test -f ".git/index"; then
+			echo ".git/index does not exist" >testfailure
+			exit 3
+		fi
+		echo "success" >testsuccess
+	EOF
+	mkdir -p dir2 &&
+	touch dir2/file1.txt &&
+	touch dir2/file2.txt &&
+	: force index to be dirty &&
+	test-tool chmtime +60 dir1/file1.txt &&
+	git status &&
+	test_path_is_file testsuccess && rm -f testsuccess &&
+	test_path_is_missing testfailure &&
+	git add . &&
+	test_path_is_file testsuccess && rm -f testsuccess &&
+	test_path_is_missing testfailure &&
+	git commit -m "second" &&
+	test_path_is_file testsuccess && rm -f testsuccess &&
+	test_path_is_missing testfailure &&
+	git checkout -- dir1/file1.txt &&
+	test_path_is_file testsuccess && rm -f testsuccess &&
+	test_path_is_missing testfailure &&
+	git update-index &&
+	test_path_is_missing testsuccess &&
+	test_path_is_missing testfailure &&
+	git reset --soft &&
+	test_path_is_missing testsuccess &&
+	test_path_is_missing testfailure
+'
+
+test_expect_success 'test checkout and reset trigger the hook' '
+	write_script .git/hooks/post-indexchanged <<-\EOF &&
+		if test "$1" -eq 1 && test "$2" -eq 1; then
+			echo "Invalid combination of flags passed to hook; updated_workdir and updated_skipworktree are both set." >testfailure
+			exit 1
+		fi
+		if test "$1" -eq 0 && test "$2" -eq 0; then
+			echo "Invalid combination of flags passed to hook; neither updated_workdir or updated_skipworktree are set." >testfailure
+			exit 2
+		fi
+		if test "$1" -eq 1; then
+			if test -f ".git/index.lock"; then
+				echo "updated_workdir set but .git/index.lock exists" >testfailure
+				exit 3
+			fi
+			if ! test -f ".git/index"; then
+				echo "updated_workdir set but .git/index does not exist" >testfailure
+				exit 3
+			fi
+		else
+			echo "update_workdir should be set for checkout" >testfailure
+			exit 4
+		fi
+		echo "success" >testsuccess
+	EOF
+	: force index to be dirty &&
+	test-tool chmtime +60 dir1/file1.txt &&
+	git checkout master &&
+	test_path_is_file testsuccess && rm -f testsuccess &&
+	test_path_is_missing testfailure &&
+	test-tool chmtime +60 dir1/file1.txt &&
+	git checkout HEAD &&
+	test_path_is_file testsuccess && rm -f testsuccess &&
+	test_path_is_missing testfailure &&
+	test-tool chmtime +60 dir1/file1.txt &&
+	git reset --hard &&
+	test_path_is_file testsuccess && rm -f testsuccess &&
+	test_path_is_missing testfailure &&
+	git checkout -B test &&
+	test_path_is_file testsuccess && rm -f testsuccess &&
+	test_path_is_missing testfailure
+'
+
+test_expect_success 'test reset --mixed and update-index triggers the hook' '
+	write_script .git/hooks/post-indexchanged <<-\EOF &&
+		if test "$1" -eq 1 && test "$2" -eq 1; then
+			echo "Invalid combination of flags passed to hook; updated_workdir and updated_skipworktree are both set." >testfailure
+			exit 1
+		fi
+		if test "$1" -eq 0 && test "$2" -eq 0; then
+			echo "Invalid combination of flags passed to hook; neither updated_workdir or updated_skipworktree are set." >testfailure
+			exit 2
+		fi
+		if test "$2" -eq 1; then
+			if test -f ".git/index.lock"; then
+				echo "updated_skipworktree set but .git/index.lock exists" >testfailure
+				exit 3
+			fi
+			if ! test -f ".git/index"; then
+				echo "updated_skipworktree set but .git/index does not exist" >testfailure
+				exit 3
+			fi
+		else
+			echo "updated_skipworktree should be set for reset --mixed and update-index" >testfailure
+			exit 4
+		fi
+		echo "success" >testsuccess
+	EOF
+	: force index to be dirty &&
+	test-tool chmtime +60 dir1/file1.txt &&
+	git reset --mixed HEAD~1 &&
+	test_path_is_file testsuccess && rm -f testsuccess &&
+	test_path_is_missing testfailure &&
+	git hash-object -w --stdin <dir1/file2.txt >expect &&
+	git update-index --cacheinfo 100644 "$(cat expect)" dir1/file1.txt &&
+	test_path_is_file testsuccess && rm -f testsuccess &&
+	test_path_is_missing testfailure &&
+	git update-index --skip-worktree dir1/file2.txt &&
+	git update-index --remove dir1/file2.txt &&
+	test_path_is_file testsuccess && rm -f testsuccess &&
+	test_path_is_missing testfailure
+'
+
+test_done
diff --git a/t/t7114-reset-sparse-checkout.sh b/t/t7114-reset-sparse-checkout.sh
new file mode 100755
index 00000000000000..8dd88fd46d3938
--- /dev/null
+++ b/t/t7114-reset-sparse-checkout.sh
@@ -0,0 +1,58 @@
+#!/bin/sh
+
+test_description='reset when using a sparse-checkout'
+
+. ./test-lib.sh
+
+# reset using a sparse-checkout file
+
+test_expect_success 'setup' '
+	test_tick &&
+	echo "checkout file" >c &&
+	echo "modify file" >m &&
+	echo "delete file" >d &&
+	git add . &&
+	git commit -m "initial commit" &&
+	echo "added file" >a &&
+	echo "modification of a file" >m &&
+	git rm d &&
+	git add . &&
+	git commit -m "second commit" &&
+	git checkout -b endCommit
+'
+
+test_expect_success 'reset when there is a sparse-checkout' '
+	echo "/c" >.git/info/sparse-checkout &&
+	test_config core.sparsecheckout true &&
+	git checkout -b resetBranch &&
+	test_path_is_missing m &&
+	test_path_is_missing a &&
+	test_path_is_missing d &&
+	git reset HEAD~1 &&
+	test "checkout file" = "$(cat c)" &&
+	test "modification of a file" = "$(cat m)" &&
+	test "added file" = "$(cat a)" &&
+	test_path_is_missing d
+'
+
+test_expect_success 'reset after deleting file without skip-worktree bit' '
+	git checkout -f endCommit &&
+	git clean -xdf &&
+	echo "/c
+/m" >.git/info/sparse-checkout &&
+	test_config core.sparsecheckout true &&
+	git checkout -b resetAfterDelete &&
+	test_path_is_file m &&
+	test_path_is_missing a &&
+	test_path_is_missing d &&
+	rm -f m &&
+	git reset HEAD~1 &&
+	test "checkout file" = "$(cat c)" &&
+	test "added file" = "$(cat a)" &&
+	test_path_is_missing m &&
+	test_path_is_missing d
+'
+
+
+
+test_done
diff --git a/t/t7523-status-complete-untracked.sh b/t/t7523-status-complete-untracked.sh
new file mode 100755
index 00000000000000..2f4476654a5570
--- /dev/null
+++ b/t/t7523-status-complete-untracked.sh
@@ -0,0 +1,39 @@
+#!/bin/sh
+
+test_description='git status untracked complete tests'
+
+. ./test-lib.sh
+
+test_expect_success 'setup' '
+	cat >.gitignore <<-\EOF &&
+	*.ign
+	ignored_dir/
+	EOF
+
+	mkdir tracked ignored_dir &&
+	touch tracked_1.txt tracked/tracked_1.txt &&
+	git add . &&
+	test_tick &&
+	git commit -m"Adding original file." &&
+	mkdir untracked &&
+	touch ignored.ign ignored_dir/ignored_2.txt \
+	      untracked_1.txt untracked/untracked_2.txt untracked/untracked_3.txt
+'
+
+test_expect_success 'verify untracked-files=complete' '
+	cat >expect <<-\EOF &&
+	? expect
+	? output
+	? untracked/
+	? untracked/untracked_2.txt
+	? untracked/untracked_3.txt
+	? untracked_1.txt
+	! ignored.ign
+	! ignored_dir/
+	EOF
+	
+	git status --porcelain=v2 --untracked-files=complete --ignored >output &&
+	test_i18ncmp expect output
+'
+
+test_done
diff --git a/t/t7524-serialized-status.sh b/t/t7524-serialized-status.sh
new file mode 100755
index 00000000000000..d157fa98d0464e
--- /dev/null
+++ b/t/t7524-serialized-status.sh
@@ -0,0 +1,336 @@
+#!/bin/sh
+
+test_description='git serialized status tests'
+
+. ./test-lib.sh
+
+# This file includes tests for serializing / deserializing
+# status data. These tests cover two basic features:
+#
+# [1] Because users can request different types of untracked-file
+#     and ignored file reporting, the cache data generated by
+#     serialize must use either the same untracked and ignored
+#     parameters as the later deserialize invocation; otherwise,
+#     the deserialize invocation must disregard the cached data
+#     and run a full scan itself.
+#
+#     To increase the number of cases where the cached status can
+#     be used, we have added a "--untracked-file=complete" option
+#     that reports a superset or union of the results from the
+#     "-u normal" and "-u all".  We combine this with a filter in
+#     deserialize to filter the results.
+#
+#     Ignored file reporting is simpler in that is an all or
+#     nothing; there are no subsets.
+#
+#     The tests here (in addition to confirming that a cache
+#     file can be generated and used by a subsequent status
+#     command) need to test this untracked-file filtering.
+#
+# [2] ensuring the status calls are using data from the status
+#     cache as expected.  This includes verifying cached data
+#     is used when appropriate as well as falling back to
+#     performing a new status scan when the data in the cache
+#     is insufficient/known stale.
+
+test_expect_success 'setup' '
+	cat >.gitignore <<-\EOF &&
+	*.ign
+	ignored_dir/
+	EOF
+
+	mkdir tracked ignored_dir &&
+	touch tracked_1.txt tracked/tracked_1.txt &&
+	git add . &&
+	test_tick &&
+	git commit -m"Adding original file." &&
+	mkdir untracked &&
+	touch ignored.ign ignored_dir/ignored_2.txt \
+	      untracked_1.txt untracked/untracked_2.txt untracked/untracked_3.txt
+'
+
+test_expect_success 'verify untracked-files=complete with no conversion' '
+	test_when_finished "rm serialized_status.dat new_change.txt output" &&
+	cat >expect <<-\EOF &&
+	? expect
+	? serialized_status.dat
+	? untracked/
+	? untracked/untracked_2.txt
+	? untracked/untracked_3.txt
+	? untracked_1.txt
+	! ignored.ign
+	! ignored_dir/
+	EOF
+	
+	git status --untracked-files=complete --ignored=matching --serialize >serialized_status.dat &&
+	touch new_change.txt &&
+
+	git status --porcelain=v2 --untracked-files=complete --ignored=matching --deserialize=serialized_status.dat >output &&
+	test_i18ncmp expect output
+'
+
+test_expect_success 'verify untracked-files=complete to untracked-files=normal conversion' '
+	test_when_finished "rm serialized_status.dat new_change.txt output" &&
+	cat >expect <<-\EOF &&
+	? expect
+	? serialized_status.dat
+	? untracked/
+	? untracked_1.txt
+	EOF
+	
+	git status --untracked-files=complete --ignored=matching --serialize >serialized_status.dat &&
+	touch new_change.txt &&
+
+	git status --porcelain=v2 --deserialize=serialized_status.dat >output &&
+	test_i18ncmp expect output
+'
+
+test_expect_success 'verify untracked-files=complete to untracked-files=all conversion' '
+	test_when_finished "rm serialized_status.dat new_change.txt output" &&
+	cat >expect <<-\EOF &&
+	? expect
+	? serialized_status.dat
+	? untracked/untracked_2.txt
+	? untracked/untracked_3.txt
+	? untracked_1.txt
+	! ignored.ign
+	! ignored_dir/
+	EOF
+	
+	git status --untracked-files=complete --ignored=matching --serialize >serialized_status.dat &&
+	touch new_change.txt &&
+
+	git status --porcelain=v2 --untracked-files=all --ignored=matching --deserialize=serialized_status.dat >output &&
+	test_i18ncmp expect output
+'
+
+test_expect_success 'verify serialized status with non-convertible ignore mode does new scan' '
+	test_when_finished "rm serialized_status.dat new_change.txt output" &&
+	cat >expect <<-\EOF &&
+	? expect
+	? new_change.txt
+	? output
+	? serialized_status.dat
+	? untracked/
+	? untracked_1.txt
+	! ignored.ign
+	! ignored_dir/
+	EOF
+	
+	git status --untracked-files=complete --ignored=matching --serialize >serialized_status.dat &&
+	touch new_change.txt &&
+
+	git status --porcelain=v2 --ignored --deserialize=serialized_status.dat >output &&
+	test_i18ncmp expect output
+'
+
+test_expect_success 'verify serialized status handles path scopes' '
+	test_when_finished "rm serialized_status.dat new_change.txt output" &&
+	cat >expect <<-\EOF &&
+	? untracked/
+	EOF
+	
+	git status --untracked-files=complete --ignored=matching --serialize >serialized_status.dat &&
+	touch new_change.txt &&
+
+	git status --porcelain=v2 --deserialize=serialized_status.dat untracked >output &&
+	test_i18ncmp expect output
+'
+
+test_expect_success 'verify no-ahead-behind and serialized status integration' '
+	test_when_finished "rm serialized_status.dat new_change.txt output" &&
+	cat >expect <<-\EOF &&
+	# branch.oid 68d4a437ea4c2de65800f48c053d4d543b55c410
+	# branch.head alt_branch
+	# branch.upstream master
+	# branch.ab +1 -0
+	? expect
+	? serialized_status.dat
+	? untracked/
+	? untracked_1.txt
+	EOF
+
+	git checkout -b alt_branch master --track >/dev/null &&
+	touch alt_branch_changes.txt &&
+	git add alt_branch_changes.txt &&
+	test_tick &&
+	git commit -m"New commit on alt branch"  &&
+
+	git status --untracked-files=complete --ignored=matching --serialize >serialized_status.dat &&
+	touch new_change.txt &&
+
+	git -c status.aheadBehind=false status --porcelain=v2 --branch --ahead-behind --deserialize=serialized_status.dat >output &&
+	test_i18ncmp expect output
+'
+
+test_expect_success 'verify new --serialize=path mode' '
+	test_when_finished "rm serialized_status.dat expect new_change.txt output.1 output.2" &&
+	cat >expect <<-\EOF &&
+	? expect
+	? output.1
+	? untracked/
+	? untracked_1.txt
+	EOF
+
+	git checkout -b serialize_path_branch master --track >/dev/null &&
+	touch alt_branch_changes.txt &&
+	git add alt_branch_changes.txt &&
+	test_tick &&
+	git commit -m"New commit on serialize_path_branch"  &&
+
+	git status --porcelain=v2 --serialize=serialized_status.dat >output.1 &&
+	touch new_change.txt &&
+
+	git status --porcelain=v2 --deserialize=serialized_status.dat >output.2 &&
+	test_i18ncmp expect output.1 &&
+	test_i18ncmp expect output.2
+'
+
+test_expect_success 'try deserialize-wait feature' '
+	test_when_finished "rm -f serialized_status.dat dirt expect.* output.* trace.*" &&
+
+	git status --serialize=serialized_status.dat >output.1 &&
+
+	# make status cache stale by updating the mtime on the index.  confirm that
+	# deserialize fails when requested.
+	sleep 1 &&
+	touch .git/index &&
+	test_must_fail git status --deserialize=serialized_status.dat --deserialize-wait=fail &&
+	test_must_fail git -c status.deserializeWait=fail status --deserialize=serialized_status.dat &&
+
+	cat >expect.1 <<-\EOF &&
+	? expect.1
+	? output.1
+	? serialized_status.dat
+	? untracked/
+	? untracked_1.txt
+	EOF
+
+	# refresh the status cache.
+	git status --porcelain=v2 --serialize=serialized_status.dat >output.1 &&
+	test_cmp expect.1 output.1 &&
+
+	# create some dirt. confirm deserialize used the existing status cache.
+	echo x >dirt &&
+	git status --porcelain=v2 --deserialize=serialized_status.dat >output.2 &&
+	test_cmp output.1 output.2 &&
+
+	# make the cache stale and try the timeout feature and wait upto
+	# 2 tenths of a second.  confirm deserialize timed out and rejected
+	# the status cache and did a normal scan.
+
+	cat >expect.2 <<-\EOF &&
+	? dirt
+	? expect.1
+	? expect.2
+	? output.1
+	? output.2
+	? serialized_status.dat
+	? trace.2
+	? untracked/
+	? untracked_1.txt
+	EOF
+
+	sleep 1 &&
+	touch .git/index &&
+	GIT_TRACE_DESERIALIZE=1 git status --porcelain=v2 --deserialize=serialized_status.dat --deserialize-wait=2 >output.2 2>trace.2 &&
+	test_cmp expect.2 output.2 &&
+	grep "wait polled=2 result=1" trace.2 >trace.2g
+'
+
+test_expect_success 'merge conflicts' '
+
+	# create a merge conflict.
+
+	git init conflicts &&
+	echo x >conflicts/x.txt &&
+	git -C conflicts add x.txt &&
+	git -C conflicts commit -m x &&
+	git -C conflicts branch a &&
+	git -C conflicts branch b &&
+	git -C conflicts checkout a &&
+	echo y >conflicts/x.txt &&
+	git -C conflicts add x.txt &&
+	git -C conflicts commit -m a &&
+	git -C conflicts checkout b &&
+	echo z >conflicts/x.txt &&
+	git -C conflicts add x.txt &&
+	git -C conflicts commit -m b &&
+	test_must_fail git -C conflicts merge --no-commit a &&
+
+	# verify that regular status correctly identifies it
+	# in each format.
+
+	cat >expect.v2 <<EOF &&
+u UU N... 100644 100644 100644 100644 587be6b4c3f93f93c489c0111bba5596147a26cb b68025345d5301abad4d9ec9166f455243a0d746 975fbec8256d3e8a3797e7a3611380f27c49f4ac x.txt
+EOF
+	git -C conflicts status --porcelain=v2 >observed.v2 &&
+	test_cmp expect.v2 observed.v2 &&
+
+	cat >expect.long <<EOF &&
+On branch b
+You have unmerged paths.
+  (fix conflicts and run "git commit")
+  (use "git merge --abort" to abort the merge)
+
+Unmerged paths:
+  (use "git add <file>..." to mark resolution)
+
+	both modified:   x.txt
+
+no changes added to commit (use "git add" and/or "git commit -a")
+EOF
+	git -C conflicts status --long >observed.long &&
+	test_cmp expect.long observed.long &&
+
+	cat >expect.short <<EOF &&
+UU x.txt
+EOF
+	git -C conflicts status --short >observed.short &&
+	test_cmp expect.short observed.short &&
+
+	# save status data in serialized cache.
+
+	git -C conflicts status --serialize >serialized &&
+
+	# make some dirt in the worktree so we can tell whether subsequent
+	# status commands used the cached data or did a fresh status.
+
+	echo dirt >conflicts/dirt.txt &&
+
+	# run status using the cached data.
+
+	git -C conflicts status --long --deserialize=../serialized >observed.long &&
+	test_cmp expect.long observed.long &&
+
+	git -C conflicts status --short --deserialize=../serialized >observed.short &&
+	test_cmp expect.short observed.short &&
+
+	# currently, the cached data does not have enough information about
+	# merge conflicts for porcelain V2 format.  (And V2 format looks at
+	# the index to get that data, but the whole point of the serialization
+	# is to avoid reading the index unnecessarily.)  So V2 always rejects
+	# the cached data when there is an unresolved conflict.
+
+	cat >expect.v2.dirty <<EOF &&
+u UU N... 100644 100644 100644 100644 587be6b4c3f93f93c489c0111bba5596147a26cb b68025345d5301abad4d9ec9166f455243a0d746 975fbec8256d3e8a3797e7a3611380f27c49f4ac x.txt
+? dirt.txt
+EOF
+	git -C conflicts status --porcelain=v2 --deserialize=../serialized >observed.v2 &&
+	test_cmp expect.v2.dirty observed.v2
+
+'
+
+test_expect_success 'renames' '
+	git init rename_test &&
+	echo OLDNAME >rename_test/OLDNAME &&
+	git -C rename_test add OLDNAME &&
+	git -C rename_test commit -m OLDNAME &&
+	git -C rename_test mv OLDNAME NEWNAME &&
+	git -C rename_test status --serialize=renamed.dat >output.1 &&
+	echo DIRT >rename_test/DIRT &&
+	git -C rename_test status --deserialize=renamed.dat >output.2 &&
+	test_i18ncmp output.1 output.2
+'
+
+test_done
diff --git a/t/t7615-merge-sparse-checkout.sh b/t/t7615-merge-sparse-checkout.sh
new file mode 100755
index 00000000000000..8e8208a61d39eb
--- /dev/null
+++ b/t/t7615-merge-sparse-checkout.sh
@@ -0,0 +1,30 @@
+#!/bin/sh
+
+test_description='merge can handle sparse-checkout'
+
+. ./test-lib.sh
+
+# merges with conflicts
+
+test_expect_success 'setup' '
+	test_commit a &&
+	test_commit file &&
+	git checkout -b delete-file &&
+	git rm file.t &&
+	test_tick &&
+	git commit -m "remove file" &&
+	git checkout master &&
+	test_commit modify file.t changed
+'
+
+test_expect_success 'merge conflict deleted file and modified' '
+	echo "/a.t" >.git/info/sparse-checkout &&
+	test_config core.sparsecheckout true &&
+	git checkout -f &&
+	test_path_is_missing file.t &&
+	test_must_fail git merge delete-file &&
+	test_path_is_file file.t &&
+	test "changed" = "$(cat file.t)"
+'
+
+test_done
diff --git a/trace2.c b/trace2.c
new file mode 100644
index 00000000000000..c9844bc742e597
--- /dev/null
+++ b/trace2.c
@@ -0,0 +1,743 @@
+#include "cache.h"
+#include "config.h"
+#include "json-writer.h"
+#include "quote.h"
+#include "run-command.h"
+#include "sigchain.h"
+#include "thread-utils.h"
+#include "version.h"
+#include "trace2/tr2_cfg.h"
+#include "trace2/tr2_dst.h"
+#include "trace2/tr2_sid.h"
+#include "trace2/tr2_tgt.h"
+#include "trace2/tr2_tls.h"
+
+static int trace2_enabled;
+
+static int tr2_next_child_id; /* modify under lock */
+static int tr2_next_repo_id = 1; /* modify under lock. zero is reserved */
+
+/*
+ * A table of the builtin TRACE2 targets.  Each of these may be independently
+ * enabled or disabled.  Each TRACE2 API will try to write an event to *each*
+ * of the enabled targets.
+ */
+static struct tr2_tgt *tr2_tgt_builtins[] =
+{
+	&tr2_tgt_normal,
+	&tr2_tgt_perf,
+	&tr2_tgt_event,
+	NULL
+};
+
+#define for_each_builtin(j, tgt_j)			\
+	for (j = 0, tgt_j = tr2_tgt_builtins[j];	\
+	     tgt_j;					\
+	     j++, tgt_j = tr2_tgt_builtins[j])
+
+#define for_each_wanted_builtin(j, tgt_j)	\
+	for_each_builtin(j, tgt_j)		\
+	if (tr2_dst_trace_want(tgt_j->pdst))
+
+/*
+ * Force (rather than lazily) initialize any of the requested
+ * builtin TRACE2 targets at startup (and before we've seen an
+ * actual TRACE2 event call) so we can see if we need to setup
+ * the TR2 and TLS machinery.
+ *
+ * Return the number of builtin targets enabled.
+ */
+static int tr2_tgt_want_builtins(void)
+{
+	struct tr2_tgt *tgt_j;
+	int j;
+	int sum = 0;
+
+	for_each_builtin(j, tgt_j) {
+		if (tgt_j->pfn_init())
+			sum++;
+	}
+
+	return sum;
+}
+
+/*
+ * Properly terminate each builtin target.  Give each target
+ * a chance to write a summary event and/or flush if necessary
+ * and then close the fd.
+ */
+static void tr2_tgt_disable_builtins(void)
+{
+	struct tr2_tgt *tgt_j;
+	int j;
+
+	for_each_builtin(j, tgt_j) {
+		tgt_j->pfn_term();
+	}
+}
+
+/*****************************************************************
+ * TODO remove this section header
+ *****************************************************************/
+
+static int tr2main_exit_code;
+
+/*
+ * Our atexit routine should run after everything has finished.
+ *
+ * Note that events generated here might not actually appear if
+ * we are writing to fd 1 or 2 and our atexit routine runs after
+ * the pager's atexit routine (since it closes them to shutdown
+ * the pipes).
+ */
+static void tr2main_atexit_handler(void)
+{
+	struct tr2_tgt *tgt_j;
+	int j;
+	uint64_t us_now;
+	uint64_t us_elapsed_absolute;
+
+	us_now = getnanotime() / 1000;
+	us_elapsed_absolute = tr2tls_absolute_elapsed(us_now);
+
+	/*
+	 * Clear any unbalanced regions so that our atexit message
+	 * does not appear nested.  This improves the appearance of
+	 * the trace output if someone calls die(), for example.
+	 */
+	tr2tls_pop_unwind_self();
+	
+	for_each_wanted_builtin(j, tgt_j) {
+		if (tgt_j->pfn_atexit)
+			tgt_j->pfn_atexit(us_elapsed_absolute,
+					  tr2main_exit_code);
+	}
+
+	tr2_tgt_disable_builtins();
+
+	tr2tls_release();
+	tr2_sid_release();
+	tr2_cfg_free_patterns();
+
+	trace2_enabled = 0;
+}
+
+static void tr2main_signal_handler(int signo)
+{
+	struct tr2_tgt *tgt_j;
+	int j;
+	uint64_t us_now;
+	uint64_t us_elapsed_absolute;
+
+	us_now = getnanotime() / 1000;
+	us_elapsed_absolute = tr2tls_absolute_elapsed(us_now);
+
+	for_each_wanted_builtin(j, tgt_j) {
+		if (tgt_j->pfn_signal)
+			tgt_j->pfn_signal(us_elapsed_absolute, signo);
+	}
+
+	sigchain_pop(signo);
+	raise(signo);
+}
+
+/*****************************************************************
+ * TODO remove this section header
+ *****************************************************************/
+
+void trace2_initialize_fl(const char *file, int line, const char **argv)
+{
+	struct tr2_tgt *tgt_j;
+	int j;
+
+	if (trace2_enabled)
+		return;
+
+	if (!tr2_tgt_want_builtins())
+		return;
+	trace2_enabled = 1;
+
+	tr2_sid_get();
+
+	atexit(tr2main_atexit_handler);
+	sigchain_push(SIGPIPE, tr2main_signal_handler);
+	tr2tls_init();
+
+	/*
+	 * Emit 'version' and 'start' messages on each active builtin target.
+	 */
+	for_each_wanted_builtin(j, tgt_j) {
+		if (tgt_j->pfn_version_fl)
+			tgt_j->pfn_version_fl(file, line);
+		if (tgt_j->pfn_start_fl)
+			tgt_j->pfn_start_fl(file, line, argv);
+	}
+}
+
+int trace2_cmd_exit_fl(const char *file, int line, int code)
+{
+	struct tr2_tgt *tgt_j;
+	int j;
+	uint64_t us_now;
+	uint64_t us_elapsed_absolute;
+
+	code &= 0xff;
+
+	if (!trace2_enabled)
+		return code;
+
+	tr2main_exit_code = code;
+
+	us_now = getnanotime() / 1000;
+	us_elapsed_absolute = tr2tls_absolute_elapsed(us_now);
+
+	for_each_wanted_builtin(j, tgt_j) {
+		if (tgt_j->pfn_exit_fl)
+			tgt_j->pfn_exit_fl(file, line, us_elapsed_absolute, code);
+	}
+
+	return code;
+}
+
+void trace2_cmd_error_va_fl(const char *file, int line,
+			    const char *fmt, va_list ap)
+{
+	struct tr2_tgt *tgt_j;
+	int j;
+
+	if (!trace2_enabled)
+		return;
+
+	/*
+	 * We expect each target function to treat 'ap' as constant
+	 * and use va_copy (because an 'ap' can only be walked once).
+	 */
+	for_each_wanted_builtin(j, tgt_j) {
+		if (tgt_j->pfn_error_va_fl)
+			tgt_j->pfn_error_va_fl(file, line, fmt, ap);
+	}
+}
+
+void trace2_cmd_path_fl(const char *file, int line, const char *pathname)
+{
+	struct tr2_tgt *tgt_j;
+	int j;
+
+	if (!trace2_enabled)
+		return;
+
+	for_each_wanted_builtin(j, tgt_j) {
+		if (tgt_j->pfn_command_path_fl)
+			tgt_j->pfn_command_path_fl(file, line, pathname);
+	}
+}
+
+void trace2_cmd_verb_fl(const char *file, int line, const char *command_verb)
+{
+	struct tr2_tgt *tgt_j;
+	int j;
+
+	if (!trace2_enabled)
+		return;
+
+	for_each_wanted_builtin(j, tgt_j) {
+		if (tgt_j->pfn_command_verb_fl)
+			tgt_j->pfn_command_verb_fl(file, line, command_verb);
+	}
+}
+
+void trace2_cmd_alias_fl(const char *file, int line,
+			 const char *alias, const char **argv)
+{
+	struct tr2_tgt *tgt_j;
+	int j;
+
+	if (!trace2_enabled)
+		return;
+
+	for_each_wanted_builtin(j, tgt_j) {
+		if (tgt_j->pfn_alias_fl)
+			tgt_j->pfn_alias_fl(file, line, alias, argv);
+	}
+}
+
+void trace2_cmd_list_config_fl(const char *file, int line)
+{
+	if (!trace2_enabled)
+		return;
+
+	tr2_cfg_list_config_fl(file, line);
+}
+
+void trace2_cmd_set_config_fl(const char *file, int line,
+			      const char *key, const char *value)
+{
+	if (!trace2_enabled)
+		return;
+
+	tr2_cfg_set_fl(file, line, key, value);
+}
+
+void trace2_child_start_fl(const char *file, int line,
+			   struct child_process *cmd)
+{
+	struct tr2_tgt *tgt_j;
+	int j;
+	uint64_t us_now;
+	uint64_t us_elapsed_absolute;
+
+	if (!trace2_enabled)
+		return;
+
+	us_now = getnanotime() / 1000;
+	us_elapsed_absolute = tr2tls_absolute_elapsed(us_now);
+
+	cmd->trace2_child_id = tr2tls_locked_increment(&tr2_next_child_id);
+	cmd->trace2_child_us_start = us_now;
+
+	for_each_wanted_builtin(j, tgt_j) {
+		if (tgt_j->pfn_child_start_fl)
+			tgt_j->pfn_child_start_fl(file, line,
+						  us_elapsed_absolute, cmd);
+	}
+}
+
+void trace2_child_exit_fl(const char *file, int line,
+			  struct child_process *cmd,
+			  int child_exit_code)
+{
+	struct tr2_tgt *tgt_j;
+	int j;
+	uint64_t us_now;
+	uint64_t us_elapsed_absolute;
+	uint64_t us_elapsed_child;
+
+	if (!trace2_enabled)
+		return;
+
+	us_now = getnanotime() / 1000;
+	us_elapsed_absolute = tr2tls_absolute_elapsed(us_now);
+	
+	if (cmd->trace2_child_us_start)
+		us_elapsed_child = us_now - cmd->trace2_child_us_start;
+	else
+		us_elapsed_child = 0;
+	
+	for_each_wanted_builtin(j, tgt_j) {
+		if (tgt_j->pfn_child_exit_fl)
+			tgt_j->pfn_child_exit_fl(
+				file, line, us_elapsed_absolute,
+				cmd->trace2_child_id,
+				child_exit_code, us_elapsed_child);
+	}
+}
+
+void trace2_exec_fl(const char *file, int line,
+		    const char *exe, const char **argv)
+{
+	struct tr2_tgt *tgt_j;
+	int j;
+	uint64_t us_now;
+	uint64_t us_elapsed_absolute;
+
+	if (!trace2_enabled)
+		return;
+
+	us_now = getnanotime() / 1000;
+	us_elapsed_absolute = tr2tls_absolute_elapsed(us_now);
+
+	for_each_wanted_builtin(j, tgt_j) {
+		if (tgt_j->pfn_exec_fl)
+			tgt_j->pfn_exec_fl(file, line, us_elapsed_absolute,
+					   exe, argv);
+	}
+}
+
+void trace2_exec_result_fl(const char *file, int line, int code)
+{
+	struct tr2_tgt *tgt_j;
+	int j;
+	uint64_t us_now;
+	uint64_t us_elapsed_absolute;
+
+	if (!trace2_enabled)
+		return;
+
+	us_now = getnanotime() / 1000;
+	us_elapsed_absolute = tr2tls_absolute_elapsed(us_now);
+
+	for_each_wanted_builtin(j, tgt_j) {
+		if (tgt_j->pfn_exec_result_fl)
+			tgt_j->pfn_exec_result_fl(file, line,
+						  us_elapsed_absolute,
+						  code);
+	}
+}
+
+void trace2_thread_start_fl(const char *file, int line,
+			    const char *thread_name)
+{
+	struct tr2_tgt *tgt_j;
+	int j;
+	uint64_t us_now;
+	uint64_t us_elapsed_absolute;
+
+	if (!trace2_enabled)
+		return;
+
+	if (tr2tls_is_main_thread())
+	{
+		/*
+		 * We should only be called from the new thread's thread-proc,
+		 * so this is technically a bug.  But in those cases where the
+		 * main thread also runs the thread-proc function (or when we
+		 * are built with threading disabled), we need to allow it.
+		 *
+		 * Convert this call to a region-enter so the nesting looks
+		 * looks correct.  
+		 */
+		trace2_region_enter_printf_fl(file, line, NULL, NULL, NULL,
+					      "thread-proc on main: %s",
+					      thread_name);
+		return;
+	}
+
+	us_now = getnanotime() / 1000;
+	us_elapsed_absolute = tr2tls_absolute_elapsed(us_now);
+
+	tr2tls_create_self(thread_name);
+
+	for_each_wanted_builtin(j, tgt_j) {
+		if (tgt_j->pfn_thread_start_fl)
+			tgt_j->pfn_thread_start_fl(file, line,
+						   us_elapsed_absolute);
+	}
+}
+
+void trace2_thread_exit_fl(const char *file, int line)
+{
+	struct tr2_tgt *tgt_j;
+	int j;
+	uint64_t us_now;
+	uint64_t us_elapsed_absolute;
+	uint64_t us_elapsed_thread;
+
+	if (!trace2_enabled)
+		return;
+
+	if (tr2tls_is_main_thread())
+	{
+		/*
+		 * We should only be called from the exiting thread's thread-proc,
+		 * so this is technically a bug.  But in those cases where the
+		 * main thread also runs the thread-proc function (or when we
+		 * are built with threading disabled), we need to allow it.
+		 *
+		 * Convert this call to a region-leave so the nesting looks
+		 * looks correct.  
+		 */
+		trace2_region_leave_printf_fl(file, line, NULL, NULL, NULL,
+					      "thread-proc on main");
+		return;
+	}
+
+	us_now = getnanotime() / 1000;
+	us_elapsed_absolute = tr2tls_absolute_elapsed(us_now);
+
+	/*
+	 * Clear any unbalanced regions and then get the relative time
+	 * for the outer-most region (which we pushed when the thread
+	 * started).  This gives us the run time of the thread.
+	 */
+	tr2tls_pop_unwind_self();
+	us_elapsed_thread = tr2tls_region_elasped_self(us_now);
+
+	for_each_wanted_builtin(j, tgt_j) {
+		if (tgt_j->pfn_thread_exit_fl)
+			tgt_j->pfn_thread_exit_fl(file, line,
+						  us_elapsed_absolute,
+						  us_elapsed_thread);
+	}
+
+	tr2tls_unset_self();
+}
+
+void trace2_def_param_fl(const char *file, int line,
+			 const char *param, const char *value)
+{
+	struct tr2_tgt *tgt_j;
+	int j;
+
+	if (!trace2_enabled)
+		return;
+
+	for_each_wanted_builtin(j, tgt_j) {
+		if (tgt_j->pfn_param_fl)
+			tgt_j->pfn_param_fl(file, line, param, value);
+	}
+}
+
+void trace2_def_repo_fl(const char *file, int line,
+			struct repository *repo)
+{
+	struct tr2_tgt *tgt_j;
+	int j;
+
+	if (!trace2_enabled)
+		return;
+
+	if (repo->trace2_repo_id)
+		return;
+
+	repo->trace2_repo_id = tr2tls_locked_increment(&tr2_next_repo_id);
+
+	for_each_wanted_builtin(j, tgt_j) {
+		if (tgt_j->pfn_repo_fl)
+			tgt_j->pfn_repo_fl(file, line, repo);
+	}
+}
+
+void trace2_region_enter_printf_va_fl(const char *file, int line,
+				      const char *category,
+				      const char *label,
+				      const struct repository *repo,
+				      const char *fmt, va_list ap)
+{
+	struct tr2_tgt *tgt_j;
+	int j;
+	uint64_t us_now;
+	uint64_t us_elapsed_absolute;
+
+	if (!trace2_enabled)
+		return;
+
+	us_now = getnanotime() / 1000;
+	us_elapsed_absolute = tr2tls_absolute_elapsed(us_now);
+
+	/*
+	 * Print the region-enter message at the current nesting
+	 * (indentation) level and then push a new level.
+	 *
+	 * We expect each target function to treat 'ap' as constant
+	 * and use va_copy.
+	 */
+	for_each_wanted_builtin(j, tgt_j) {
+		if (tgt_j->pfn_region_enter_printf_va_fl)
+			tgt_j->pfn_region_enter_printf_va_fl(
+				file, line, us_elapsed_absolute,
+				category, label, repo, fmt, ap);
+	}
+
+	tr2tls_push_self(us_now);
+}
+
+void trace2_region_enter_fl(const char *file, int line,
+			    const char *category,
+			    const char *label,
+			    const struct repository *repo)
+{
+	trace2_region_enter_printf_va_fl(file, line,
+					 category, label, repo,
+					 NULL, NULL);
+}
+
+void trace2_region_enter_printf_fl(const char *file, int line,
+				   const char *category,
+				   const char *label,
+				   const struct repository *repo,
+				   const char *fmt, ...)
+{
+	va_list ap;
+
+	va_start(ap, fmt);
+	trace2_region_enter_printf_va_fl(file, line,
+					 category, label, repo,
+					 fmt, ap);
+	va_end(ap);
+}
+
+#ifndef HAVE_VARIADIC_MACROS
+void trace2_region_enter_printf(const char *category, const char *label,
+				const struct repository *repo,
+				const char *fmt, ...)
+{
+	va_list ap;
+
+	va_start(ap, fmt);
+	trace2_region_enter_printf_va_fl(NULL, 0,
+					 category, label, repo,
+					 fmt, ap);
+	va_end(ap);
+}
+#endif
+
+void trace2_region_leave_printf_va_fl(const char *file, int line,
+				      const char *category,
+				      const char *label,
+				      const struct repository *repo,
+				      const char *fmt, va_list ap)
+{
+	struct tr2_tgt *tgt_j;
+	int j;
+	uint64_t us_now;
+	uint64_t us_elapsed_absolute;
+	uint64_t us_elapsed_region;
+
+	if (!trace2_enabled)
+		return;
+
+	us_now = getnanotime() / 1000;
+	us_elapsed_absolute = tr2tls_absolute_elapsed(us_now);
+
+	/*
+	 * Get the elapsed time in the current region before we
+	 * pop it off the stack.  Pop the stack.  And then print
+	 * the perf message at the new (shallower) level so that
+	 * it lines up with the corresponding push/enter.
+	 */
+	us_elapsed_region = tr2tls_region_elasped_self(us_now);
+	
+	tr2tls_pop_self();
+
+	/*
+	 * We expect each target function to treat 'ap' as constant
+	 * and use va_copy.
+	 */
+	for_each_wanted_builtin(j, tgt_j) {
+		if (tgt_j->pfn_region_leave_printf_va_fl)
+			tgt_j->pfn_region_leave_printf_va_fl(
+				file, line, us_elapsed_absolute,
+				us_elapsed_region,
+				category, label, repo,
+				fmt, ap);
+	}
+}
+
+void trace2_region_leave_fl(const char *file, int line,
+			    const char *category,
+			    const char *label,
+			    const struct repository *repo)
+{
+	trace2_region_leave_printf_va_fl(file, line,
+					 category, label, repo,
+					 NULL, NULL);
+}
+
+void trace2_region_leave_printf_fl(const char *file, int line,
+				   const char *category,
+				   const char *label,
+				   const struct repository *repo,
+				   const char *fmt, ...)
+{
+	va_list ap;
+
+	va_start(ap, fmt);
+	trace2_region_leave_printf_va_fl(file, line,
+					 category, label, repo,
+					 fmt, ap);
+	va_end(ap);
+}
+
+#ifndef HAVE_VARIADIC_MACROS
+void trace2_region_leave_printf(const char *category, const char *label,
+				const struct repository *repo,
+				const char *fmt, ...)
+{
+	va_list ap;
+
+	va_start(ap, fmt);
+	trace2_region_leave_printf_va_fl(NULL, 0,
+					 category, label, repo,
+					 fmt, ap);
+	va_end(ap);
+}
+#endif
+
+void trace2_data_string_fl(const char *file, int line,
+			   const char *category,
+			   const struct repository *repo,
+			   const char *key,
+			   const char *value)
+{
+	struct tr2_tgt *tgt_j;
+	int j;
+	uint64_t us_now;
+	uint64_t us_elapsed_absolute;
+	uint64_t us_elapsed_region;
+
+	if (!trace2_enabled)
+		return;
+
+	us_now = getnanotime() / 1000;
+	us_elapsed_absolute = tr2tls_absolute_elapsed(us_now);
+	us_elapsed_region = tr2tls_region_elasped_self(us_now);
+
+	for_each_wanted_builtin(j, tgt_j) {
+		if (tgt_j->pfn_data_fl)
+			tgt_j->pfn_data_fl(file, line, us_elapsed_absolute,
+					   us_elapsed_region,
+					   category, repo, key, value);
+	}
+}
+
+void trace2_data_intmax_fl(const char *file, int line,
+			   const char *category,
+			   const struct repository *repo,
+			   const char *key,
+			   intmax_t value)
+{
+	struct strbuf buf_string = STRBUF_INIT;
+
+	if (!trace2_enabled)
+		return;
+
+	strbuf_addf(&buf_string, "%"PRIdMAX, value);
+	trace2_data_string_fl(file, line, category, repo, key, buf_string.buf);
+	strbuf_release(&buf_string);
+}
+
+void trace2_printf_va_fl(const char *file, int line,
+			 const char *fmt, va_list ap)
+{
+	struct tr2_tgt *tgt_j;
+	int j;
+	uint64_t us_now;
+	uint64_t us_elapsed_absolute;
+
+	if (!trace2_enabled)
+		return;
+
+	us_now = getnanotime() / 1000;
+	us_elapsed_absolute = tr2tls_absolute_elapsed(us_now);
+
+	/*
+	 * We expect each target function to treat 'ap' as constant
+	 * and use va_copy.
+	 */
+	for_each_wanted_builtin(j, tgt_j) {
+		if (tgt_j->pfn_printf_va_fl)
+			tgt_j->pfn_printf_va_fl(file, line, us_elapsed_absolute,
+						fmt, ap);
+	}
+}
+
+void trace2_printf_fl(const char *file, int line,
+		      const char *fmt, ...)
+{
+	va_list ap;
+
+	va_start(ap, fmt);
+	trace2_printf_va_fl(file, line, fmt, ap);
+	va_end(ap);
+}
+
+#ifndef HAVE_VARIADIC_MACROS
+void trace2_printf(const char *fmt, ...)
+{
+	va_list ap;
+
+	va_start(ap, fmt);
+	trace2_printf_va_fl(NULL, 0, fmt, ap);
+	va_end(ap);
+}
+#endif
diff --git a/trace2.h b/trace2.h
new file mode 100644
index 00000000000000..8cb75a57305307
--- /dev/null
+++ b/trace2.h
@@ -0,0 +1,353 @@
+#ifndef TRACE2_H
+#define TRACE2_H
+
+struct child_process;
+struct repository;
+
+/*
+ * The public TRACE2 routines are grouped into the following groups:
+ *
+ * [] trace2_initialize -- initialization.
+ * [] trace2_cmd_*      -- emit command/control messages.
+ * [] trace2_child*     -- emit child start/stop messages.
+ * [] trace2_exec*      -- emit exec start/stop messages.
+ * [] trace2_thread*    -- emit thread start/stop messages.
+ * [] trace2_def*       -- emit definition/parameter mesasges.
+ * [] trace2_region*    -- emit region nesting messages.
+ * [] trace2_data*      -- emit region/thread/repo data messages.
+ * [] trace2_printf*    -- legacy trace[1] messages.
+ */
+
+
+/*
+ * Initialize TRACE2 tracing facility if any of the builtin TRACE2
+ * targets are enabled in the environment.  Emits 'version' and
+ * 'start' events.
+ *
+ * Cleanup/Termination is handled automatically by a registered
+ * atexit() routine.
+ */
+void trace2_initialize_fl(const char *file, int line, const char **argv);
+
+#define trace2_initialize(argv) trace2_initialize_fl(__FILE__, __LINE__, argv)
+
+/*
+ * Emit an 'exit' event.
+ *
+ * Write the exit-code that will be passed to exit() or returned
+ * from main().
+ *
+ * Use this prior to actually calling exit().
+ * See "#define exit()" in git-compat-util.h
+ */
+int trace2_cmd_exit_fl(const char *file, int line, int code);
+
+#define trace2_cmd_exit(code) (trace2_cmd_exit_fl(__FILE__, __LINE__, (code)))
+
+/*
+ * Emit an 'error' event.
+ *
+ * Write an error message to the TRACE2 targets.
+ */
+void trace2_cmd_error_va_fl(const char *file, int line,
+			    const char *fmt, va_list ap);
+
+#define trace2_cmd_error_va(fmt, ap) \
+	trace2_cmd_error_va_fl(__FILE__, __LINE__, (fmt), (ap))
+
+/*
+ * Emit a 'pathname' event with the canonical pathname of the current process
+ * This gives post-processors a simple field to identify the command without
+ * having to parse the argv.  For example, to distinguish invocations from
+ * installed versus debug executables.
+ */
+void trace2_cmd_path_fl(const char *file, int line, const char *pathname);
+
+#define trace2_cmd_path(p) \
+	trace2_cmd_path_fl(__FILE__, __LINE__, (p))
+
+/*
+ * Emit a 'cmd_verb' event with the canonical name of the (usually)
+ * builtin command.  This gives post-processors a simple field
+ * to identify the command verb without having to parse the argv.
+ */
+void trace2_cmd_verb_fl(const char *file, int line, const char *command_verb);
+
+#define trace2_cmd_verb(v) \
+	trace2_cmd_verb_fl(__FILE__, __LINE__, (v))
+
+/*
+ * Emit an 'alias' expansion event.
+ */
+void trace2_cmd_alias_fl(const char *file, int line,
+			 const char *alias, const char **argv);
+
+#define trace2_cmd_alias(alias, argv) \
+	trace2_cmd_alias_fl(__FILE__, __LINE__, (alias), (argv))
+
+/*
+ * Emit one or more 'def_param' events for "interesting" configuration
+ * settings.
+ *
+ * The environment variable "GIT_TR2_CONFIG_PARAMS" can be set to a
+ * list of patterns considered important.  For example:
+ *
+ *    GIT_TR2_CONFIG_PARAMS="core.*,remote.*.url"
+ *
+ * Note: this routine does a read-only iteration on the config data
+ * (using read_early_config()), so it must not be called until enough
+ * of the process environment has been established.  This includes the
+ * location of the git and worktree directories, expansion of any "-c"
+ * and "-C" command line options, and etc.
+ */
+void trace2_cmd_list_config_fl(const char *file, int line);
+
+#define trace2_cmd_list_config() \
+	trace2_cmd_list_config_fl(__FILE__, __LINE__)
+
+/*
+ * Emit a "def_param" event for the given config key/value pair IF
+ * we consider the key to be "interesting".
+ *
+ * Use this for new/updated config settings created/updated after
+ * trace2_cmd_list_config() is called.
+ */
+void trace2_cmd_set_config_fl(const char *file, int line,
+			      const char *key, const char *value);
+
+#define trace2_cmd_set_config(k, v) \
+	trace2_cmd_set_config_fl(__FILE__, __LINE__, (k), (v))
+
+/*
+ * Emit a 'child_start' event prior to spawning a child process.
+ *
+ * Before calling optionally set "cmd->trace2_child_class" to a string
+ * describing the type of the child process.  For example, "editor" or
+ * "pager".
+ */
+void trace2_child_start_fl(const char *file, int line,
+			   struct child_process *cmd);
+
+#define trace2_child_start(cmd) \
+	trace2_child_start_fl(__FILE__, __LINE__, (cmd))
+
+/*
+ * Emit a 'child_exit' event after the child process completes. 
+ */
+void trace2_child_exit_fl(const char *file, int line,
+			  struct child_process *cmd,
+			  int child_exit_code);
+
+#define trace2_child_exit(cmd, code) \
+	trace2_child_exit_fl(__FILE__, __LINE__, (cmd), (code))
+
+/*
+ * Emit an 'exec' event prior to calling one of exec(), execv(),
+ * execvp(), and etc.  On Unix-derived systems, this will be the
+ * last event emitted for the current process, unless the exec
+ * fails.  On Windows, exec() behaves like 'child_start' and a
+ * waitpid(), so additional events may be emitted.
+ */
+void trace2_exec_fl(const char *file, int line,
+		    const char *exe, const char **argv);
+
+#define trace2_exec(exe, argv) \
+	trace2_exec_fl(__FILE__, __LINE__, (exe), (argv))
+
+/*
+ * Emit an 'exec_result' when possible.  On Unix-derived systems,
+ * this should be called after exec() returns (which only happens
+ * when there is an error starting the new process).  On Windows,
+ * this should be called after the waitpid().
+ */
+void trace2_exec_result_fl(const char *file, int line, int code);
+
+#define trace2_exec_result(code) \
+	trace2_exec_result_fl(__FILE__, __LINE__, (code))
+
+/*
+ * Emit a 'thread_start' event.  This must be called from inside the
+ * thread-proc to set up the trace2 TLS data for the thread.
+ *
+ * Thread names should be descriptive, like "preload_index".
+ * Thread names will be decorated with an instance number automatically.
+ */
+void trace2_thread_start_fl(const char *file, int line,
+				 const char *thread_name);
+
+#define trace2_thread_start(thread_name) \
+	trace2_thread_start_fl(__FILE__, __LINE__, (thread_name))
+
+/*
+ * Emit a 'thread_exit' event.  This must be called from inside the
+ * thread-proc to report thread-specific data and cleanup TLS data
+ * for the thread.
+ */
+void trace2_thread_exit_fl(const char *file, int line);
+
+#define trace2_thread_exit() trace2_thread_exit_fl(__FILE__, __LINE__)
+
+/*
+ * Emit a 'param' event.
+ *
+ * Write a "<param> = <value>" pair describing some aspect of the
+ * run such as an important configuration setting or command line
+ * option that significantly changes command behavior.
+ */ 
+void trace2_def_param_fl(const char *file, int line,
+			 const char *param, const char *value);
+
+#define trace2_def_param(param, value) \
+	trace2_def_param_fl(__FILE__, __LINE__, (param), (value))
+
+/*
+ * Tell trace2 about a newly instantiated repo object and assign
+ * a trace2-repo-id to be used in subsequent activity events.
+ *
+ * Emits a 'worktree' event for this repo instance.
+ */
+void trace2_def_repo_fl(const char *file, int line,
+			struct repository *repo);
+
+#define trace2_def_repo(repo) \
+	trace2_def_repo_fl(__FILE__, __LINE__, repo)
+
+/*
+ * Emit a 'region_enter' event for <category>.<label> with optional
+ * repo-id and printf message.
+ *
+ * Enter a new nesting level on the current thread and remember the
+ * current time.  This controls the indenting of all subsequent events
+ * on this thread.
+ */
+void trace2_region_enter_fl(const char *file, int line,
+			    const char *category,
+			    const char *label,
+			    const struct repository *repo);
+
+#define trace2_region_enter(category, label, repo) \
+	trace2_region_enter_fl( \
+		__FILE__, __LINE__, (category), (label), (repo))
+
+void trace2_region_enter_printf_va_fl(const char *file, int line,
+				      const char *category,
+				      const char *label,
+				      const struct repository *repo,
+				      const char *fmt, va_list ap);
+
+#define trace2_region_enter_printf_va(category, label, repo, fmt, ap) \
+	trace2_region_enter_printf_va_fl( \
+		__FILE__, __LINE__, (category), (label), (repo), (fmt), (ap))
+
+void trace2_region_enter_printf_fl(const char *file, int line,
+				   const char *category, const char *label,
+				   const struct repository *repo,
+				   const char *fmt, ...);
+
+#ifdef HAVE_VARIADIC_MACROS
+#define trace2_region_enter_printf(category, label, repo, ...) \
+	trace2_region_enter_printf_fl( \
+		__FILE__, __LINE__, (category), (label), (repo), __VA_ARGS__)
+#else
+__attribute__((format (region_enter_printf, 4, 5)))
+void trace2_region_enter_printf(const char *category, const char *label,
+				const struct repository *repo,
+				const char *fmt, ...);
+#endif
+
+/*
+ * Emit a 'region_leave' event for <category>.<label> with optional
+ * repo-id and printf message.
+ *
+ * Leave current nesting level and report the elapsed time spent
+ * in this nesting level.
+ */
+void trace2_region_leave_fl(const char *file, int line,
+			    const char *category,
+			    const char *label,
+			    const struct repository *repo);
+
+#define trace2_region_leave(category, label, repo) \
+	trace2_region_leave_fl( \
+		__FILE__, __LINE__, (category), (label), (repo))
+
+void trace2_region_leave_printf_va_fl(const char *file, int line,
+				      const char *category,
+				      const char *label,
+				      const struct repository *repo,
+				      const char *fmt, va_list ap);
+
+#define trace2_region_leave_printf_va(category, label, repo, fmt, ap) \
+	trace2_region_leave_printf_va_fl( \
+		__FILE__, __LINE__, (category), (label), (repo), (fmt), (ap))
+
+void trace2_region_leave_printf_fl(const char *file, int line,
+				   const char *category, const char *label,
+				   const struct repository *repo,
+				   const char *fmt, ...);
+
+#ifdef HAVE_VARIADIC_MACROS
+#define trace2_region_leave_printf(category, label, repo, ...) \
+	trace2_region_leave_printf_fl( \
+		__FILE__, __LINE__, (category), (label), (repo), __VA_ARGS__)
+#else
+__attribute__((format (region_leave_printf, 4, 5)))
+void trace2_region_leave_printf(const char *category, const char *label,
+				const struct repository *repo,
+				const char *fmt, ...);
+#endif
+
+/*
+ * Emit a key-value pair 'data' event of the form <category>.<key> = <value>.
+ * This event implicitly contains information about thread, nesting region,
+ * and optional repo-id.
+ *
+ * On event-based TRACE2 targets, this generates a 'data' event suitable
+ * for post-processing.  On printf-based TRACE2 targets, this is converted
+ * into a fixed-format printf message.
+ */
+void trace2_data_string_fl(const char *file, int line,
+			   const char *category,
+			   const struct repository *repo,
+			   const char *key,
+			   const char *value);
+
+#define trace2_data_string(category, repo, key, value) \
+	trace2_data_string_fl( \
+		__FILE__, __LINE__, (category), (repo), (key), (value))
+
+void trace2_data_intmax_fl(const char *file, int line,
+			   const char *category,
+			   const struct repository *repo,
+			   const char *key,
+			   intmax_t value);
+
+#define trace2_data_intmax(category, repo, key, value) \
+	trace2_data_intmax_fl( \
+		__FILE__, __LINE__, (category), (repo), (key), (value))
+
+/*
+ * Emit a 'printf' event.
+ *
+ * Write an arbitrary formatted message to the TRACE2 targets.  These
+ * text messages should be considered as human-readable strings without
+ * any formatting guidelines.  Post-processors may choose to ignore
+ * them.
+ */
+void trace2_printf_va_fl(const char *file, int line,
+			 const char *fmt, va_list ap);
+
+#define trace2_printf_va(fmt, ap) \
+	trace2_printf_va_fl(__FILE__, __LINE__, (fmt), (ap))
+
+void trace2_printf_fl(const char *file, int line, const char *fmt, ...);
+
+#ifdef HAVE_VARIADIC_MACROS
+#define trace2_printf(...) \
+	trace2_printf_fl(__FILE__, __LINE__, __VA_ARGS__)
+#else
+__attribute__((format (printf, 1, 2)))
+void trace2_printf(const char *fmt, ...);
+#endif
+
+#endif /* TRACE2_H */
diff --git a/trace2/tr2_cfg.c b/trace2/tr2_cfg.c
new file mode 100644
index 00000000000000..0f16ed09f701f1
--- /dev/null
+++ b/trace2/tr2_cfg.c
@@ -0,0 +1,92 @@
+#include "cache.h"
+#include "config.h"
+#include "tr2_cfg.h"
+
+#define TR2_CFG_PARAM "GIT_TR2_CONFIG_PARAMS"
+
+static struct strbuf **tr2_cfg_patterns;
+static int tr2_cfg_count_patterns;
+static int tr2_cfg_loaded;
+
+/*
+ * Parse a string containing a comma-delimited list of config keys
+ * or wildcard patterns into a list of strbufs.
+ */
+static int tr2_cfg_load_patterns(void)
+{
+	struct strbuf **s;
+	const char *envvar;
+
+	if (tr2_cfg_loaded)
+		return tr2_cfg_count_patterns;
+	tr2_cfg_loaded = 1;
+
+	envvar = getenv(TR2_CFG_PARAM);
+	if (!envvar || !*envvar)
+		return tr2_cfg_count_patterns;
+
+	tr2_cfg_patterns = strbuf_split_buf(envvar, strlen(envvar), ',', -1);
+	for (s = tr2_cfg_patterns; *s; s++) {
+		struct strbuf *buf = *s;
+
+		if (buf->len && buf->buf[buf->len - 1] == ',')
+			strbuf_setlen(buf, buf->len - 1);
+		strbuf_trim_trailing_newline(*s);
+		strbuf_trim(*s);
+	}
+
+	tr2_cfg_count_patterns = s - tr2_cfg_patterns;
+	return tr2_cfg_count_patterns;
+}
+
+void tr2_cfg_free_patterns(void)
+{
+	if (tr2_cfg_patterns)
+		strbuf_list_free(tr2_cfg_patterns);
+	tr2_cfg_count_patterns = 0;
+	tr2_cfg_loaded = 0;
+}
+
+struct tr2_cfg_data
+{
+	const char *file;
+	int line;
+};
+
+/*
+ * See if the given config key matches any of our patterns of interest.
+ */
+static int tr2_cfg_cb(const char *key, const char *value, void *d)
+{
+	struct strbuf **s;
+	struct tr2_cfg_data *data = (struct tr2_cfg_data *)d;
+
+	for (s = tr2_cfg_patterns; *s; s++) {
+		struct strbuf *buf = *s;
+		int wm = wildmatch(buf->buf, key, WM_CASEFOLD);
+		if (wm == WM_MATCH) {
+			trace2_def_param_fl(data->file, data->line, key, value);
+			return 0;
+		}
+	}
+
+	return 0;
+}
+
+void tr2_cfg_list_config_fl(const char *file, int line)
+{
+	struct tr2_cfg_data data = { file, line };
+
+	if (tr2_cfg_load_patterns() > 0)
+		read_early_config(tr2_cfg_cb, &data);
+}
+
+void tr2_cfg_set_fl(const char *file, int line,
+		    const char *key, const char *value)
+{
+	struct tr2_cfg_data data = { file, line };
+
+	if (tr2_cfg_load_patterns() > 0)
+		tr2_cfg_cb(key, value, &data);
+}
+
diff --git a/trace2/tr2_cfg.h b/trace2/tr2_cfg.h
new file mode 100644
index 00000000000000..1e3db7e496a782
--- /dev/null
+++ b/trace2/tr2_cfg.h
@@ -0,0 +1,23 @@
+#ifndef TR2_CFG_H
+#define TR2_CFG_H
+
+/*
+ * This file contains "private/protected" declarations for TRACE2.
+ */
+
+/*
+ * Iterate over all config settings and emit 'def_param' events for the
+ * "interesting" ones to TRACE2.
+ */
+void tr2_cfg_list_config_fl(const char *file, int line);
+
+/*
+ * Emit a "def_param" event for the given key/value pair IF we consider
+ * the key to be "interesting".
+ */
+void tr2_cfg_set_fl(const char *file, int line,
+		    const char *key, const char *value);
+
+void tr2_cfg_free_patterns(void);
+
+#endif /* TR2_CFG_H */
diff --git a/trace2/tr2_dst.c b/trace2/tr2_dst.c
new file mode 100644
index 00000000000000..e68c62629d2f5a
--- /dev/null
+++ b/trace2/tr2_dst.c
@@ -0,0 +1,87 @@
+#include "cache.h"
+#include "trace2/tr2_dst.h"
+
+/*
+ * This file contains "private/protected" declarations for TRACE2.
+ */
+
+void tr2_dst_trace_disable(struct tr2_dst *dst)
+{
+	if (dst->need_close)
+		close(dst->fd);
+	dst->fd = 0;
+	dst->initialized = 1;
+	dst->need_close = 0;
+}
+
+int tr2_dst_get_trace_fd(struct tr2_dst *dst)
+{
+	const char *trace;
+
+	/* don't open twice */
+	if (dst->initialized)
+		return dst->fd;
+
+	trace = getenv(dst->env_var_name);
+
+	if (!trace || !strcmp(trace, "") ||
+	    !strcmp(trace, "0") || !strcasecmp(trace, "false"))
+		dst->fd = 0;
+	else if (!strcmp(trace, "1") || !strcasecmp(trace, "true"))
+		dst->fd = STDERR_FILENO;
+	else if (strlen(trace) == 1 && isdigit(*trace))
+		dst->fd = atoi(trace);
+	else if (is_absolute_path(trace)) {
+		int fd = open(trace, O_WRONLY | O_APPEND | O_CREAT, 0666);
+		if (fd == -1) {
+			warning("could not open '%s' for tracing: %s",
+				trace, strerror(errno));
+			tr2_dst_trace_disable(dst);
+		} else {
+			dst->fd = fd;
+			dst->need_close = 1;
+		}
+	} else {
+		warning("unknown trace value for '%s': %s\n"
+			"         If you want to trace into a file, then please set %s\n"
+			"         to an absolute pathname (starting with /)",
+			dst->env_var_name, trace, dst->env_var_name);
+		tr2_dst_trace_disable(dst);
+	}
+
+	dst->initialized = 1;
+	return dst->fd;
+}
+
+int tr2_dst_trace_want(struct tr2_dst *dst)
+{
+	return !!tr2_dst_get_trace_fd(dst);
+}
+
+void tr2_dst_write_line(struct tr2_dst *dst, struct strbuf *buf_line)
+{
+	strbuf_complete_line(buf_line); /* ensure final NL on buffer */
+
+	/*
+	 * We do not use write_in_full() because we do not want
+	 * a short-write to try again.  We are using O_APPEND mode
+	 * files and the kernel handles the atomic seek+write. If
+	 * another thread or git process is concurrently writing to
+	 * this fd or file, our remainder-write may not be contiguous
+	 * with our initial write of this message.  And that will
+	 * confuse readers.  So just don't bother.
+	 *
+	 * It is assumed that TRACE2 messages are short enough that
+	 * the system can write them in 1 attempt and we won't see
+	 * a short-write.
+	 *
+	 * If we get an IO error, just close the trace dst.
+	 */
+
+	if (write(tr2_dst_get_trace_fd(dst),
+		  buf_line->buf, buf_line->len) < 0) {
+		warning("unable to write trace for '%s': %s",
+			dst->env_var_name, strerror(errno));
+		tr2_dst_trace_disable(dst);
+	}
+}
diff --git a/trace2/tr2_dst.h b/trace2/tr2_dst.h
new file mode 100644
index 00000000000000..90902a664cf62c
--- /dev/null
+++ b/trace2/tr2_dst.h
@@ -0,0 +1,34 @@
+#ifndef TR2_DST_H
+#define TR2_DST_H
+
+struct tr2_dst {
+	const char * const env_var_name;
+	int fd;
+	unsigned int initialized : 1;
+	unsigned int  need_close : 1;
+};
+
+/*
+ * Disable TRACE2 on the destination.  In TRACE2 a destination (DST)
+ * wraps a file descriptor; it is associated with a TARGET which
+ * defines the formatting.
+ */
+void tr2_dst_trace_disable(struct tr2_dst *dst);
+
+/*
+ * Return the file descriptor for the DST.
+ * If 0, the dst is closed or disabled.
+ */
+int tr2_dst_get_trace_fd(struct tr2_dst *dst);
+
+/*
+ * Return true if the DST is opened for writing.
+ */
+int tr2_dst_trace_want(struct tr2_dst *dst);
+
+/*
+ * Write a single line/message to the trace file.
+ */
+void tr2_dst_write_line(struct tr2_dst *dst, struct strbuf *buf_line);
+
+#endif /* TR2_DST_H */
diff --git a/trace2/tr2_sid.c b/trace2/tr2_sid.c
new file mode 100644
index 00000000000000..7fba400e9766f6
--- /dev/null
+++ b/trace2/tr2_sid.c
@@ -0,0 +1,69 @@
+#include "cache.h"
+#include "trace2/tr2_sid.h"
+
+/*
+ * This file contains "private/protected" routines for TRACE2.
+ */
+
+static struct strbuf tr2sid_buf = STRBUF_INIT;
+static int tr2sid_nr_git_parents;
+
+/*
+ * Compute a "unique" session id (SID) for the current process.  This allows
+ * all events from this process to have a single label (much like a PID).
+ *
+ * Export this into our environment so that all child processes inherit it.
+ *
+ * If we were started by another git instance, use our parent's SID as a
+ * prefix.  (This lets us track parent/child relationships even if there
+ * is an intermediate shell process.)
+ *
+ * Additionally, count the number of nested git processes.
+ */
+static void tr2_sid_compute(void)
+{
+	uint64_t us_now;
+	const char *parent_sid;
+
+	if (tr2sid_buf.len)
+		return;
+
+	parent_sid = getenv("SLOG_PARENT_SID");
+	if (parent_sid && *parent_sid) {
+		const char *p;
+		for (p = parent_sid; *p; p++)
+			if (*p == '/')
+				tr2sid_nr_git_parents++;
+
+		strbuf_addstr(&tr2sid_buf, parent_sid);
+		strbuf_addch(&tr2sid_buf, '/');
+		tr2sid_nr_git_parents++;
+	}
+
+	us_now = getnanotime() / 1000;
+	strbuf_addf(&tr2sid_buf, "%"PRIuMAX"-%"PRIdMAX,
+		    (uintmax_t)us_now, (intmax_t)getpid());
+
+	setenv("SLOG_PARENT_SID", tr2sid_buf.buf, 1);
+}
+
+const char *tr2_sid_get(void)
+{
+	if (!tr2sid_buf.len)
+		tr2_sid_compute();
+
+	return tr2sid_buf.buf;
+}
+
+int tr2_sid_depth(void)
+{
+	if (!tr2sid_buf.len)
+		tr2_sid_compute();
+
+	return tr2sid_nr_git_parents;
+}
+
+void tr2_sid_release(void)
+{
+	strbuf_release(&tr2sid_buf);
+}
diff --git a/trace2/tr2_sid.h b/trace2/tr2_sid.h
new file mode 100644
index 00000000000000..30fc14b894be02
--- /dev/null
+++ b/trace2/tr2_sid.h
@@ -0,0 +1,22 @@
+#ifndef TR2_SID_H
+#define TR2_SID_H
+
+/*
+ * This file contains "private/protected" declarations for TRACE2.
+ */
+
+/*
+ * Get our session id. Compute if necessary.
+ */
+const char *tr2_sid_get(void);
+
+/*
+ * Get our process depth.  A top-level git process invoked from the
+ * command line will have depth=0.  A child git process will have
+ * depth=1 and so on.
+ */
+int tr2_sid_depth(void);
+
+void tr2_sid_release(void);
+
+#endif /* TR2_SID_H */
diff --git a/trace2/tr2_tbuf.c b/trace2/tr2_tbuf.c
new file mode 100644
index 00000000000000..98c4c25770adb8
--- /dev/null
+++ b/trace2/tr2_tbuf.c
@@ -0,0 +1,17 @@
+#include "cache.h"
+#include "tr2_tbuf.h"
+
+void tr2_tbuf_current_time(struct tr2_tbuf *tb)
+{
+	struct timeval tv;
+	struct tm tm;
+	time_t secs;
+
+	gettimeofday(&tv, NULL);
+	secs = tv.tv_sec;
+	localtime_r(&secs, &tm);
+
+	xsnprintf(tb->buf, sizeof(tb->buf), "%02d:%02d:%02d.%06ld",
+		  tm.tm_hour, tm.tm_min, tm.tm_sec, (long)tv.tv_usec);
+}
+
diff --git a/trace2/tr2_tbuf.h b/trace2/tr2_tbuf.h
new file mode 100644
index 00000000000000..63a035b6e9fa94
--- /dev/null
+++ b/trace2/tr2_tbuf.h
@@ -0,0 +1,19 @@
+#ifndef TR2_TBUF_H
+#define TR2_TBUF_H
+
+/*
+ * This file contains "private/protected" declarations for TRACE2.
+ */
+
+/*
+ * A simple wrapper around a fixed buffer to avoid C syntax
+ * quirks and the need to pass around an additional size_t
+ * argument.
+ */
+struct tr2_tbuf {
+	char buf[24];
+};
+
+void tr2_tbuf_current_time(struct tr2_tbuf *tb);
+
+#endif /* TR2_TBUF_H */
diff --git a/trace2/tr2_tgt.h b/trace2/tr2_tgt.h
new file mode 100644
index 00000000000000..9d93add2236a69
--- /dev/null
+++ b/trace2/tr2_tgt.h
@@ -0,0 +1,119 @@
+#ifndef TR2_TGT_H
+#define TR2_TGT_H
+
+/*
+ * This file contains "private/protected" declarations for TRACE2.
+ */
+
+/*
+ * Function prototypes for a TRACE2 "target" vtable.
+ */
+
+typedef int (tr2_tgt_init_t)(void);
+typedef void (tr2_tgt_term_t)(void);
+
+typedef void (tr2_tgt_evt_version_fl_t)
+	(const char *file, int line);
+
+typedef void (tr2_tgt_evt_start_fl_t)
+	(const char *file, int line, const char **argv);
+typedef void (tr2_tgt_evt_exit_fl_t)
+	(const char *file, int line, uint64_t us_elapsed_absolute, int code);
+typedef void (tr2_tgt_evt_signal_t)
+	(uint64_t us_elapsed_absolute, int signo);
+typedef void (tr2_tgt_evt_atexit_t)
+	(uint64_t us_elapsed_absolute, int code);
+
+typedef void (tr2_tgt_evt_error_va_fl_t)
+	(const char *file, int line, const char *fmt, va_list ap);
+
+typedef void (tr2_tgt_evt_command_path_fl_t)
+	(const char *file, int line, const char *command_path);
+typedef void (tr2_tgt_evt_command_verb_fl_t)
+	(const char *file, int line, const char *command_verb);
+
+typedef void (tr2_tgt_evt_alias_fl_t)
+	(const char *file, int line, const char *alias, const char **argv);
+
+typedef void (tr2_tgt_evt_child_start_fl_t)
+	(const char *file, int line, uint64_t us_elapsed_absolute,
+	 const struct child_process *cmd);
+typedef void (tr2_tgt_evt_child_exit_fl_t)
+	(const char *file, int line, uint64_t us_elapsed_absolute, int cid,
+	 int code, uint64_t us_elapsed_child);
+
+typedef void (tr2_tgt_evt_thread_start_fl_t)
+	(const char *file, int line, uint64_t us_elapsed_absolute);
+typedef void (tr2_tgt_evt_thread_exit_fl_t)
+	(const char *file, int line, uint64_t us_elapsed_absolute,
+	 uint64_t us_elapsed_thread);
+
+typedef void (tr2_tgt_evt_exec_fl_t)
+	(const char *file, int line, uint64_t us_elapsed_absolute,
+	 const char *exe, const char **argv);
+typedef void (tr2_tgt_evt_exec_result_fl_t)
+	(const char *file, int line, uint64_t us_elapsed_absolute, int code);
+
+typedef void (tr2_tgt_evt_param_fl_t)
+	(const char *file, int line, const char *param, const char *value);
+
+typedef void (tr2_tgt_evt_repo_fl_t)
+	(const char *file, int line, const struct repository *repo);
+
+typedef void (tr2_tgt_evt_region_enter_printf_va_fl_t)
+	(const char *file, int line, uint64_t us_elapsed_absolute,
+	 const char *category, const char *label, const struct repository *repo,
+	 const char *fmt, va_list ap);
+typedef void (tr2_tgt_evt_region_leave_printf_va_fl_t)
+	(const char *file, int line, uint64_t us_elapsed_absolute,
+	 uint64_t us_elapsed_region, const char *category, const char *label,
+	 const struct repository *repo, const char *fmt, va_list ap);
+
+typedef void (tr2_tgt_evt_data_fl_t)
+	(const char *file, int line, uint64_t us_elapsed_absolute,
+	 uint64_t us_elapsed_region, const char *category,
+	 const struct repository *repo, const char *key, const char *value);
+
+typedef void (tr2_tgt_evt_printf_va_fl_t)
+	(const char *file, int line, uint64_t us_elapsed_absolute,
+	 const char *fmt, va_list ap);
+
+/*
+ * "vtable" for a TRACE2 target.  Use NULL if a target does not want
+ * to emit that message.
+ */
+struct tr2_tgt
+{
+	struct tr2_dst                          *pdst;
+
+	tr2_tgt_init_t                          *pfn_init;
+	tr2_tgt_term_t                          *pfn_term;
+
+	tr2_tgt_evt_version_fl_t                *pfn_version_fl;
+	tr2_tgt_evt_start_fl_t                  *pfn_start_fl;
+	tr2_tgt_evt_exit_fl_t                   *pfn_exit_fl;
+	tr2_tgt_evt_signal_t                    *pfn_signal;
+	tr2_tgt_evt_atexit_t                    *pfn_atexit;
+	tr2_tgt_evt_error_va_fl_t               *pfn_error_va_fl;
+	tr2_tgt_evt_command_path_fl_t           *pfn_command_path_fl;
+	tr2_tgt_evt_command_verb_fl_t           *pfn_command_verb_fl;
+	tr2_tgt_evt_alias_fl_t                  *pfn_alias_fl;
+	tr2_tgt_evt_child_start_fl_t            *pfn_child_start_fl;
+	tr2_tgt_evt_child_exit_fl_t             *pfn_child_exit_fl;
+	tr2_tgt_evt_thread_start_fl_t           *pfn_thread_start_fl;
+	tr2_tgt_evt_thread_exit_fl_t            *pfn_thread_exit_fl;
+	tr2_tgt_evt_exec_fl_t                   *pfn_exec_fl;
+	tr2_tgt_evt_exec_result_fl_t            *pfn_exec_result_fl;
+	tr2_tgt_evt_param_fl_t                  *pfn_param_fl;
+	tr2_tgt_evt_repo_fl_t                   *pfn_repo_fl;
+	tr2_tgt_evt_region_enter_printf_va_fl_t *pfn_region_enter_printf_va_fl;
+	tr2_tgt_evt_region_leave_printf_va_fl_t *pfn_region_leave_printf_va_fl;
+	tr2_tgt_evt_data_fl_t                   *pfn_data_fl;
+	tr2_tgt_evt_printf_va_fl_t              *pfn_printf_va_fl;
+};
+
+extern struct tr2_tgt tr2_tgt_event;
+extern struct tr2_tgt tr2_tgt_normal;
+extern struct tr2_tgt tr2_tgt_perf;
+
+#endif /* TR2_TGT_H */
diff --git a/trace2/tr2_tgt_event.c b/trace2/tr2_tgt_event.c
new file mode 100644
index 00000000000000..9e653d111b9846
--- /dev/null
+++ b/trace2/tr2_tgt_event.c
@@ -0,0 +1,531 @@
+#include "cache.h"
+#include "config.h"
+#include "json-writer.h"
+#include "run-command.h"
+#include "version.h"
+#include "trace2/tr2_dst.h"
+#include "trace2/tr2_tbuf.h"
+#include "trace2/tr2_sid.h"
+#include "trace2/tr2_tgt.h"
+#include "trace2/tr2_tls.h"
+
+/*
+ * This file contains "private/protected" declarations for TRACE2.
+ */
+
+static struct tr2_dst tr2dst_event  = { "GIT_TR2_EVENT", 0, 0, 0 };
+
+/*
+ * The version number of the JSON data generated by the EVENT target
+ * in this source file.  Update this if you make a significant change
+ * to the JSON fields or message structure.  You probably do not need
+ * to update this if you just add another call to one of the existing
+ * TRACE2 API methods.
+ */
+#define GIT_TR2_EVENT_VERSION "1"
+
+/*
+ * Region nesting limit for messages written to the event target.
+ *
+ * The "region_enter" and "region_leave" messages (especially recursive
+ * messages such as those produced while diving the worktree or index)
+ * are primarily intended for the performance target during debugging.
+ *
+ * Some of the outer-most messages, however, may be of interest to the
+ * event target.  Set this environment variable to a larger integer for
+ * more detail in the event target.
+ */
+#define GIT_TR2_EVENT_NESTING "GIT_TR2_EVENT_NESTING"
+static int tr2env_event_nesting_wanted = 2;
+
+static int fn_init(void)
+{
+	int want = tr2_dst_trace_want(&tr2dst_event);
+	int want_nesting;
+	char *nesting;
+
+	if (!want)
+		return want;
+
+	nesting = getenv(GIT_TR2_EVENT_NESTING);
+	if (nesting && ((want_nesting = atoi(nesting)) > 0))
+		tr2env_event_nesting_wanted = want_nesting;
+
+	return want;
+}
+
+static void fn_term(void)
+{
+	tr2_dst_trace_disable(&tr2dst_event);
+}
+
+/*
+ * Append common key-value pairs to the currently open JSON object.
+ *     "event:"<event_name>"
+ *      "sid":"<sid>"
+ *   "thread":"<thread_name>"
+ *     "time":"<time>"
+ *     "file":"<filename>"
+ *     "line":<line_number>
+ *     "repo":<repo_id>
+ */
+static void event_fmt_prepare(const char *event_name,
+			      const char *file, int line,
+			      const struct repository *repo,
+			      struct json_writer *jw)
+{
+	struct tr2tls_thread_ctx *ctx = tr2tls_get_self();
+	struct tr2_tbuf tb_now;
+
+	jw_object_string(jw, "event", event_name);
+	jw_object_string(jw, "sid", tr2_sid_get());
+	jw_object_string(jw, "thread", ctx->thread_name.buf);
+
+	tr2_tbuf_current_time(&tb_now);
+	jw_object_string(jw, "time", tb_now.buf);
+
+	if (file && *file) {
+		jw_object_string(jw, "file", file);
+		jw_object_intmax(jw, "line", line);
+	}
+
+	if (repo)
+		jw_object_intmax(jw, "repo", repo->trace2_repo_id);
+}
+
+static void fn_version_fl(const char *file, int line)
+{
+	const char *event_name = "version";
+	struct json_writer jw = JSON_WRITER_INIT;
+
+	jw_object_begin(&jw, 0);
+	event_fmt_prepare(event_name, file, line, NULL, &jw);
+	jw_object_string(&jw, "evt", GIT_TR2_EVENT_VERSION);
+	jw_object_string(&jw, "exe", git_version_string);
+	jw_end(&jw);
+
+	tr2_dst_write_line(&tr2dst_event, &jw.json);
+	jw_release(&jw);
+}
+
+static void fn_start_fl(const char *file, int line, const char **argv)
+{
+	const char *event_name = "start";
+	struct json_writer jw = JSON_WRITER_INIT;
+
+	jw_object_begin(&jw, 0);
+	event_fmt_prepare(event_name, file, line, NULL, &jw);
+	jw_object_inline_begin_array(&jw, "argv");
+	jw_array_argv(&jw, argv);
+	jw_end(&jw);
+	jw_end(&jw);
+
+	tr2_dst_write_line(&tr2dst_event, &jw.json);
+	jw_release(&jw);
+}
+
+static void fn_exit_fl(const char *file, int line,
+		       uint64_t us_elapsed_absolute, int code)
+{
+	const char *event_name = "exit";
+	struct json_writer jw = JSON_WRITER_INIT;
+	double t_abs = (double)us_elapsed_absolute / 1000000.0;
+
+	jw_object_begin(&jw, 0);
+	event_fmt_prepare(event_name, file, line, NULL, &jw);
+	jw_object_double(&jw, "t_abs", 6, t_abs);
+	jw_object_intmax(&jw, "code", code);
+	jw_end(&jw);
+
+	tr2_dst_write_line(&tr2dst_event, &jw.json);
+	jw_release(&jw);
+}
+
+static void fn_signal(uint64_t us_elapsed_absolute, int signo)
+{
+	const char *event_name = "signal";
+	struct json_writer jw = JSON_WRITER_INIT;
+	double t_abs = (double)us_elapsed_absolute / 1000000.0;
+
+	jw_object_begin(&jw, 0);
+	event_fmt_prepare(event_name, __FILE__, __LINE__, NULL, &jw);
+	jw_object_double(&jw, "t_abs", 6, t_abs);
+	jw_object_intmax(&jw, "signo", signo);
+	jw_end(&jw);
+
+	tr2_dst_write_line(&tr2dst_event, &jw.json);
+	jw_release(&jw);
+}
+
+static void fn_atexit(uint64_t us_elapsed_absolute, int code)
+{
+	const char *event_name = "atexit";
+	struct json_writer jw = JSON_WRITER_INIT;
+	double t_abs = (double)us_elapsed_absolute / 1000000.0;
+
+	jw_object_begin(&jw, 0);
+	event_fmt_prepare(event_name, __FILE__, __LINE__, NULL, &jw);
+	jw_object_double(&jw, "t_abs", 6, t_abs);
+	jw_object_intmax(&jw, "code", code);
+	jw_end(&jw);
+
+	tr2_dst_write_line(&tr2dst_event, &jw.json);
+	jw_release(&jw);
+}
+
+static void maybe_add_string_va(struct json_writer *jw,
+				const char *field_name,
+				const char *fmt, va_list ap)
+{
+	if (fmt && *fmt && ap) {
+		va_list copy_ap;
+		struct strbuf buf = STRBUF_INIT;
+
+		va_copy(copy_ap, ap);
+		strbuf_vaddf(&buf, fmt, copy_ap);
+		va_end(copy_ap);
+
+		jw_object_string(jw, field_name, buf.buf);
+		strbuf_release(&buf);
+		return;
+	}
+
+	if (fmt && *fmt) {
+		jw_object_string(jw, field_name, fmt);
+		return;
+	}
+}
+
+static void fn_error_va_fl(const char *file, int line,
+			   const char *fmt, va_list ap)
+{
+	const char *event_name = "error";
+	struct json_writer jw = JSON_WRITER_INIT;
+
+	jw_object_begin(&jw, 0);
+	event_fmt_prepare(event_name, file, line, NULL, &jw);
+	maybe_add_string_va(&jw, "msg", fmt, ap);
+	/*
+	 * Also emit the format string as a field in case
+	 * post-processors want to aggregate common error
+	 * messages by type without argument fields (such
+	 * as pathnames or branch names) cluttering it up.
+	 */
+	if (fmt && *fmt)
+		jw_object_string(&jw, "fmt", fmt);
+	jw_end(&jw);
+
+	tr2_dst_write_line(&tr2dst_event, &jw.json);
+	jw_release(&jw);
+}
+
+static void fn_command_path_fl(const char *file, int line,
+			       const char *pathname)
+{
+	const char *event_name = "cmd_path";
+	struct json_writer jw = JSON_WRITER_INIT;
+
+	jw_object_begin(&jw, 0);
+	event_fmt_prepare(event_name, file, line, NULL, &jw);
+	jw_object_string(&jw, "path", pathname);
+	jw_end(&jw);
+
+	tr2_dst_write_line(&tr2dst_event, &jw.json);
+	jw_release(&jw);
+}
+
+static void fn_command_verb_fl(const char *file, int line,
+			       const char *command_verb)
+{
+	const char *event_name = "cmd_verb";
+	struct json_writer jw = JSON_WRITER_INIT;
+
+	jw_object_begin(&jw, 0);
+	event_fmt_prepare(event_name, file, line, NULL, &jw);
+	jw_object_string(&jw, "name", command_verb);
+	jw_end(&jw);
+
+	tr2_dst_write_line(&tr2dst_event, &jw.json);
+	jw_release(&jw);
+}
+
+static void fn_alias_fl(const char *file, int line,
+			const char *alias, const char **argv)
+{
+	const char *event_name = "alias";
+	struct json_writer jw = JSON_WRITER_INIT;
+
+	jw_object_begin(&jw, 0);
+	event_fmt_prepare(event_name, file, line, NULL, &jw);
+	jw_object_string(&jw, "alias", alias);
+	jw_object_inline_begin_array(&jw, "argv");
+	jw_array_argv(&jw, argv);
+	jw_end(&jw);
+	jw_end(&jw);
+
+	tr2_dst_write_line(&tr2dst_event, &jw.json);
+	jw_release(&jw);
+}
+
+static void fn_child_start_fl(const char *file, int line,
+			      uint64_t us_elapsed_absolute,
+			      const struct child_process *cmd)
+{
+	const char *event_name = "child_start";
+	struct json_writer jw = JSON_WRITER_INIT;
+	const char *child_class = ((cmd->trace2_child_class) ?
+				   cmd->trace2_child_class : "?");
+
+	jw_object_begin(&jw, 0);
+	event_fmt_prepare(event_name, file, line, NULL, &jw);
+	jw_object_intmax(&jw, "child_id", cmd->trace2_child_id);
+	jw_object_string(&jw, "child_class", child_class);
+	if (cmd->dir)
+		jw_object_string(&jw, "cd", cmd->dir);
+	jw_object_bool(&jw, "use_shell", cmd->use_shell);
+	jw_object_inline_begin_array(&jw, "argv");
+	if (cmd->git_cmd)
+		jw_array_string(&jw, "git");
+	jw_array_argv(&jw, cmd->argv);
+	jw_end(&jw);
+	jw_end(&jw);
+
+	tr2_dst_write_line(&tr2dst_event, &jw.json);
+	jw_release(&jw);
+}
+
+static void fn_child_exit_fl(const char *file, int line,
+			     uint64_t us_elapsed_absolute,
+			     int cid, int code,
+			     uint64_t us_elapsed_child)
+{
+	const char *event_name = "child_exit";
+	struct json_writer jw = JSON_WRITER_INIT;
+	double t_rel = (double)us_elapsed_child / 1000000.0;
+
+	jw_object_begin(&jw, 0);
+	event_fmt_prepare(event_name, file, line, NULL, &jw);
+	jw_object_intmax(&jw, "child_id", cid);
+	jw_object_intmax(&jw, "code", code);
+	jw_object_double(&jw, "t_rel", 6, t_rel);
+	jw_end(&jw);
+
+	tr2_dst_write_line(&tr2dst_event, &jw.json);
+
+	jw_release(&jw);
+}
+
+static void fn_thread_start_fl(const char *file, int line,
+			       uint64_t us_elapsed_absolute)
+{
+	const char *event_name = "thread_start";
+	struct json_writer jw = JSON_WRITER_INIT;
+
+	jw_object_begin(&jw, 0);
+	event_fmt_prepare(event_name, file, line, NULL, &jw);
+	jw_end(&jw);
+
+	tr2_dst_write_line(&tr2dst_event, &jw.json);
+	jw_release(&jw);
+}
+
+static void fn_thread_exit_fl(const char *file, int line,
+			      uint64_t us_elapsed_absolute,
+			      uint64_t us_elapsed_thread)
+{
+	const char *event_name = "thread_exit";
+	struct json_writer jw = JSON_WRITER_INIT;
+	double t_rel = (double)us_elapsed_thread / 1000000.0;
+
+	jw_object_begin(&jw, 0);
+	event_fmt_prepare(event_name, file, line, NULL, &jw);
+	jw_object_double(&jw, "t_rel", 6, t_rel);
+	jw_end(&jw);
+
+	tr2_dst_write_line(&tr2dst_event, &jw.json);
+	jw_release(&jw);
+}
+
+static void fn_exec_fl(const char *file, int line,
+		       uint64_t us_elapsed_absolute,
+		       const char *exe, const char **argv)
+{
+	const char *event_name = "exec";
+	struct json_writer jw = JSON_WRITER_INIT;
+
+	jw_object_begin(&jw, 0);
+	event_fmt_prepare(event_name, file, line, NULL, &jw);
+	if (exe)
+		jw_object_string(&jw, "exe", exe);
+	jw_object_inline_begin_array(&jw, "argv");
+	jw_array_argv(&jw, argv);
+	jw_end(&jw);
+	jw_end(&jw);
+
+	tr2_dst_write_line(&tr2dst_event, &jw.json);
+	jw_release(&jw);
+}
+
+static void fn_exec_result_fl(const char *file, int line,
+			      uint64_t us_elapsed_absolute, int code)
+{
+	const char *event_name = "exec_result";
+	struct json_writer jw = JSON_WRITER_INIT;
+
+	jw_object_begin(&jw, 0);
+	event_fmt_prepare(event_name, file, line, NULL, &jw);
+	jw_object_intmax(&jw, "code", code);
+	jw_end(&jw);
+
+	tr2_dst_write_line(&tr2dst_event, &jw.json);
+	jw_release(&jw);
+}
+
+static void fn_param_fl(const char *file, int line,
+			const char *param, const char *value)
+{
+	const char *event_name = "def_param";
+	struct json_writer jw = JSON_WRITER_INIT;
+
+	jw_object_begin(&jw, 0);
+	event_fmt_prepare(event_name, file, line, NULL, &jw);
+	jw_object_string(&jw, "param", param);
+	jw_object_string(&jw, "value", value);
+	jw_end(&jw);
+
+	tr2_dst_write_line(&tr2dst_event, &jw.json);
+	jw_release(&jw);
+}
+
+static void fn_repo_fl(const char *file, int line,
+		       const struct repository *repo)
+{
+	const char *event_name = "def_repo";
+	struct json_writer jw = JSON_WRITER_INIT;
+
+	jw_object_begin(&jw, 0);
+	event_fmt_prepare(event_name, file, line, repo, &jw);
+	jw_object_string(&jw, "worktree", repo->worktree);
+	jw_end(&jw);
+
+	tr2_dst_write_line(&tr2dst_event, &jw.json);
+	jw_release(&jw);
+}
+
+static void fn_region_enter_printf_va_fl(const char *file, int line,
+					 uint64_t us_elapsed_absolute,
+					 const char *category,
+					 const char *label,
+					 const struct repository *repo,
+					 const char *fmt, va_list ap)
+{
+	const char *event_name = "region_enter";
+	struct tr2tls_thread_ctx *ctx = tr2tls_get_self();
+	if (ctx->nr_open_regions <= tr2env_event_nesting_wanted) {
+		struct json_writer jw = JSON_WRITER_INIT;
+
+		jw_object_begin(&jw, 0);
+		event_fmt_prepare(
+			event_name, file, line, repo, &jw);
+		jw_object_intmax(&jw, "nesting", ctx->nr_open_regions);
+		if (category)
+			jw_object_string(&jw, "category", category);
+		if (label)
+			jw_object_string(&jw, "label", label);
+		maybe_add_string_va(&jw, "msg", fmt, ap);
+		jw_end(&jw);
+
+		tr2_dst_write_line(&tr2dst_event, &jw.json);
+		jw_release(&jw);
+	}
+}
+
+static void fn_region_leave_printf_va_fl(const char *file, int line,
+					 uint64_t us_elapsed_absolute,
+					 uint64_t us_elapsed_region,
+					 const char *category,
+					 const char *label,
+					 const struct repository *repo,
+					 const char *fmt, va_list ap)
+{
+	const char *event_name = "region_leave";
+	struct tr2tls_thread_ctx *ctx = tr2tls_get_self();
+	if (ctx->nr_open_regions <= tr2env_event_nesting_wanted) {
+		struct json_writer jw = JSON_WRITER_INIT;
+		double t_rel = (double)us_elapsed_region / 1000000.0;
+
+		jw_object_begin(&jw, 0);
+		event_fmt_prepare(event_name, file, line, repo, &jw);
+		jw_object_double(&jw, "t_rel", 6, t_rel);
+		jw_object_intmax(&jw, "nesting", ctx->nr_open_regions);
+		if (category)
+			jw_object_string(&jw, "category", category);
+		if (label)
+			jw_object_string(&jw, "label", label);
+		maybe_add_string_va(&jw, "msg", fmt, ap);
+		jw_end(&jw);
+
+		tr2_dst_write_line(&tr2dst_event, &jw.json);
+		jw_release(&jw);
+	}
+}
+
+static void fn_data_fl(const char *file, int line,
+		       uint64_t us_elapsed_absolute,
+		       uint64_t us_elapsed_region,
+		       const char *category,
+		       const struct repository *repo,
+		       const char *key,
+		       const char *value)
+{
+	const char *event_name = "data";
+	struct tr2tls_thread_ctx *ctx = tr2tls_get_self();
+	if (ctx->nr_open_regions <= tr2env_event_nesting_wanted) {
+		struct json_writer jw = JSON_WRITER_INIT;
+		double t_abs = (double)us_elapsed_absolute / 1000000.0;
+		double t_rel = (double)us_elapsed_region / 1000000.0;
+
+		jw_object_begin(&jw, 0);
+		event_fmt_prepare(event_name, file, line, repo, &jw);
+		jw_object_double(&jw, "t_abs", 6, t_abs);
+		jw_object_double(&jw, "t_rel", 6, t_rel);
+		jw_object_intmax(&jw, "nesting", ctx->nr_open_regions);
+		jw_object_string(&jw, "category", category);
+		jw_object_string(&jw, "key", key);
+		jw_object_string(&jw, "value", value);
+		jw_end(&jw);
+
+		tr2_dst_write_line(&tr2dst_event, &jw.json);
+		jw_release(&jw);
+	}
+}
+
+struct tr2_tgt tr2_tgt_event =
+{
+	&tr2dst_event,
+
+	fn_init,
+	fn_term,
+
+	fn_version_fl,
+	fn_start_fl,
+	fn_exit_fl,
+	fn_signal,
+	fn_atexit,
+	fn_error_va_fl,
+	fn_command_path_fl,
+	fn_command_verb_fl,
+	fn_alias_fl,
+	fn_child_start_fl,
+	fn_child_exit_fl,
+	fn_thread_start_fl,
+	fn_thread_exit_fl,
+	fn_exec_fl,
+	fn_exec_result_fl,
+	fn_param_fl,
+	fn_repo_fl,
+	fn_region_enter_printf_va_fl,
+	fn_region_leave_printf_va_fl,
+	fn_data_fl,
+	NULL, /* printf */
+};
diff --git a/trace2/tr2_tgt_normal.c b/trace2/tr2_tgt_normal.c
new file mode 100644
index 00000000000000..bab32100630273
--- /dev/null
+++ b/trace2/tr2_tgt_normal.c
@@ -0,0 +1,320 @@
+#include "cache.h"
+#include "config.h"
+#include "run-command.h"
+#include "quote.h"
+#include "version.h"
+#include "trace2/tr2_dst.h"
+#include "trace2/tr2_tbuf.h"
+#include "trace2/tr2_tgt.h"
+#include "trace2/tr2_tls.h"
+
+/*
+ * This file contains "private/protected" declarations for TRACE2.
+ */
+
+static struct tr2_dst tr2dst_normal = { "GIT_TR2", 0, 0, 0 };
+
+/*
+ * Set this environment variable to true to omit the "<time> <file>:<line>"
+ * fields from each line written to the builtin normal target.
+ *
+ * Unit tests may want to use this to help with testing.
+ */
+#define GIT_TR2_NORMAL_BARE "GIT_TR2_BARE"
+static int tr2env_normal_bare;
+
+#define TR2FMT_NORMAL_FL_WIDTH       (50)
+
+static int fn_init(void)
+{
+	int want = tr2_dst_trace_want(&tr2dst_normal);
+	int want_bare;
+	char *bare;
+
+	if (!want)
+		return want;
+
+	bare = getenv(GIT_TR2_NORMAL_BARE);
+	if (bare && *bare &&
+	    ((want_bare = git_parse_maybe_bool(bare)) != -1))
+		tr2env_normal_bare = want_bare;
+
+	return want;
+}
+
+static void fn_term(void)
+{
+	tr2_dst_trace_disable(&tr2dst_normal);
+}
+
+static void normal_fmt_prepare(const char *file, int line, struct strbuf *buf)
+{
+	strbuf_setlen(buf,0);
+
+	if (!tr2env_normal_bare) {
+		struct tr2_tbuf tb_now;
+
+		tr2_tbuf_current_time(&tb_now);
+		strbuf_addstr(buf, tb_now.buf);
+		strbuf_addch(buf, ' ');
+
+		if (file && *file)
+			strbuf_addf(buf, "%s:%d ", file, line);
+		while (buf->len < TR2FMT_NORMAL_FL_WIDTH)
+			strbuf_addch(buf, ' ');
+	}
+}
+
+static void normal_io_write_fl(const char *file, int line,
+			       const struct strbuf *buf_payload)
+{
+	struct strbuf buf_line = STRBUF_INIT;
+
+	normal_fmt_prepare(file, line, &buf_line);
+	strbuf_addbuf(&buf_line, buf_payload);
+	tr2_dst_write_line(&tr2dst_normal, &buf_line);
+	strbuf_release(&buf_line);
+}
+
+static void fn_version_fl(const char *file, int line)
+{
+	struct strbuf buf_payload = STRBUF_INIT;
+
+	strbuf_addf(&buf_payload, "version %s", git_version_string);
+	normal_io_write_fl(file, line, &buf_payload);
+	strbuf_release(&buf_payload);
+}
+
+static void fn_start_fl(const char *file, int line, const char **argv)
+{
+	struct strbuf buf_payload = STRBUF_INIT;
+
+	strbuf_addstr(&buf_payload, "start ");
+	sq_quote_argv_pretty(&buf_payload, argv);
+	normal_io_write_fl(file, line, &buf_payload);
+	strbuf_release(&buf_payload);
+}
+
+static void fn_exit_fl(const char *file, int line,
+		       uint64_t us_elapsed_absolute, int code)
+{
+	struct strbuf buf_payload = STRBUF_INIT;
+	double elapsed = (double)us_elapsed_absolute / 1000000.0;
+
+	strbuf_addf(&buf_payload, "exit elapsed:%.6f code:%d",
+		    elapsed, code);
+	normal_io_write_fl(file, line, &buf_payload);
+	strbuf_release(&buf_payload);
+}
+
+static void fn_signal(uint64_t us_elapsed_absolute, int signo)
+{
+	struct strbuf buf_payload = STRBUF_INIT;
+	double elapsed = (double)us_elapsed_absolute / 1000000.0;
+
+	strbuf_addf(&buf_payload, "signal elapsed:%.6f code:%d",
+		    elapsed, signo);
+	normal_io_write_fl(__FILE__, __LINE__, &buf_payload);
+	strbuf_release(&buf_payload);
+}
+
+static void fn_atexit(uint64_t us_elapsed_absolute, int code)
+{
+	struct strbuf buf_payload = STRBUF_INIT;
+	double elapsed = (double)us_elapsed_absolute / 1000000.0;
+
+	strbuf_addf(&buf_payload, "atexit elapsed:%.6f code:%d",
+		    elapsed, code);
+	normal_io_write_fl(__FILE__, __LINE__, &buf_payload);
+	strbuf_release(&buf_payload);
+}
+
+static void maybe_append_string_va(struct strbuf *buf,
+				   const char *fmt, va_list ap)
+{
+	if (fmt && *fmt && ap) {
+		va_list copy_ap;
+
+		va_copy(copy_ap, ap);
+		strbuf_vaddf(buf, fmt, copy_ap);
+		va_end(copy_ap);
+		return;
+	}
+
+	if (fmt && *fmt) {
+		strbuf_addstr(buf, fmt);
+		return;
+	}
+}
+
+static void fn_error_va_fl(const char *file, int line,
+			   const char *fmt, va_list ap)
+{
+	struct strbuf buf_payload = STRBUF_INIT;
+
+	strbuf_addstr(&buf_payload, "error ");
+	maybe_append_string_va(&buf_payload, fmt, ap);
+	normal_io_write_fl(file, line, &buf_payload);
+	strbuf_release(&buf_payload);
+}
+
+static void fn_command_path_fl(const char *file, int line,
+			       const char *pathname)
+{
+	struct strbuf buf_payload = STRBUF_INIT;
+
+	strbuf_addf(&buf_payload, "cmd_path %s", pathname);
+	normal_io_write_fl(file, line, &buf_payload);
+	strbuf_release(&buf_payload);
+}
+
+static void fn_command_verb_fl(const char *file, int line,
+			       const char *command_verb)
+{
+	struct strbuf buf_payload = STRBUF_INIT;
+
+	strbuf_addf(&buf_payload, "cmd_verb %s", command_verb);
+	normal_io_write_fl(file, line, &buf_payload);
+	strbuf_release(&buf_payload);
+}
+
+static void fn_alias_fl(const char *file, int line, const char *alias,
+			const char **argv)
+{
+	struct strbuf buf_payload = STRBUF_INIT;
+
+	strbuf_addf(&buf_payload, "alias %s ->", alias);
+	sq_quote_argv_pretty(&buf_payload, argv);
+	normal_io_write_fl(file, line, &buf_payload);
+	strbuf_release(&buf_payload);
+}
+
+static void fn_child_start_fl(const char *file, int line,
+			      uint64_t us_elapsed_absolute,
+			      const struct child_process *cmd)
+{
+	struct strbuf buf_payload = STRBUF_INIT;
+
+	strbuf_addf(&buf_payload, "child_start[%d] ", cmd->trace2_child_id);
+
+	if (cmd->dir) {
+		strbuf_addstr(&buf_payload, " cd");
+		sq_quote_buf_pretty(&buf_payload, cmd->dir);
+		strbuf_addstr(&buf_payload, "; ");
+	}
+
+	/*
+	 * TODO if (cmd->env) { Consider dumping changes to environment. }
+	 * See trace_add_env() in run-command.c as used by original trace.c
+	 */
+
+	if (cmd->git_cmd)
+		strbuf_addstr(&buf_payload, "git");
+	sq_quote_argv_pretty(&buf_payload, cmd->argv);
+
+	normal_io_write_fl(file, line, &buf_payload);
+	strbuf_release(&buf_payload);
+}
+
+static void fn_child_exit_fl(const char *file, int line,
+			     uint64_t us_elapsed_absolute,
+			     int cid, int code,
+			     uint64_t us_elapsed_child)
+{
+	struct strbuf buf_payload = STRBUF_INIT;
+	double elapsed = (double)us_elapsed_child / 1000000.0;
+
+	strbuf_addf(&buf_payload, "child_exit[%d] code:%d elapsed:%.6f",
+		    cid, code, elapsed);
+	normal_io_write_fl(file, line, &buf_payload);
+	strbuf_release(&buf_payload);
+}
+
+static void fn_exec_fl(const char *file, int line,
+		       uint64_t us_elapsed_absolute,
+		       const char *exe, const char **argv)
+{
+	struct strbuf buf_payload = STRBUF_INIT;
+
+	strbuf_addstr(&buf_payload, "exec ");
+	if (exe)
+		strbuf_addstr(&buf_payload, exe);
+	sq_quote_argv_pretty(&buf_payload, argv);
+	normal_io_write_fl(file, line, &buf_payload);
+	strbuf_release(&buf_payload);
+}
+
+static void fn_exec_result_fl(const char *file, int line,
+			      uint64_t us_elapsed_absolute,
+			      int code)
+{
+	struct strbuf buf_payload = STRBUF_INIT;
+
+	strbuf_addf(&buf_payload, "exec_result code:%d", code);
+	if (code > 0)
+		strbuf_addf(&buf_payload, " err:%s", strerror(code));
+	normal_io_write_fl(file, line, &buf_payload);
+	strbuf_release(&buf_payload);
+}
+
+static void fn_param_fl(const char *file, int line, const char *param,
+			const char *value)
+{
+	struct strbuf buf_payload = STRBUF_INIT;
+
+	strbuf_addf(&buf_payload, "def_param %s=%s", param, value);
+	normal_io_write_fl(file, line, &buf_payload);
+	strbuf_release(&buf_payload);
+}
+
+static void fn_repo_fl(const char *file, int line,
+		       const struct repository *repo)
+{
+	struct strbuf buf_payload = STRBUF_INIT;
+
+	strbuf_addstr(&buf_payload, "worktree ");
+	sq_quote_buf_pretty(&buf_payload, repo->worktree);
+	normal_io_write_fl(file, line, &buf_payload);
+	strbuf_release(&buf_payload);
+}
+
+static void fn_printf_va_fl(const char *file, int line,
+			    uint64_t us_elapsed_absolute,
+			    const char *fmt, va_list ap)
+{
+	struct strbuf buf_payload = STRBUF_INIT;
+
+	maybe_append_string_va(&buf_payload, fmt, ap);
+	normal_io_write_fl(file, line, &buf_payload);
+	strbuf_release(&buf_payload);
+}
+
+struct tr2_tgt tr2_tgt_normal =
+{
+	&tr2dst_normal,
+
+	fn_init,
+	fn_term,
+
+	fn_version_fl,
+	fn_start_fl,
+	fn_exit_fl,
+	fn_signal,
+	fn_atexit,
+	fn_error_va_fl,
+	fn_command_path_fl,
+	fn_command_verb_fl,
+	fn_alias_fl,
+	fn_child_start_fl,
+	fn_child_exit_fl,
+	NULL, /* thread_start */
+	NULL, /* thread_exit */
+	fn_exec_fl,
+	fn_exec_result_fl,
+	fn_param_fl,
+	fn_repo_fl,
+	NULL, /* region_enter */
+	NULL, /* region_leave */
+	NULL, /* data */
+	fn_printf_va_fl,
+};
diff --git a/trace2/tr2_tgt_perf.c b/trace2/tr2_tgt_perf.c
new file mode 100644
index 00000000000000..f2b8089a8c8156
--- /dev/null
+++ b/trace2/tr2_tgt_perf.c
@@ -0,0 +1,530 @@
+#include "cache.h"
+#include "config.h"
+#include "run-command.h"
+#include "quote.h"
+#include "version.h"
+#include "trace2/tr2_dst.h"
+#include "trace2/tr2_sid.h"
+#include "trace2/tr2_tbuf.h"
+#include "trace2/tr2_tgt.h"
+#include "trace2/tr2_tls.h"
+
+/*
+ * This file contains "private/protected" declarations for TRACE2.
+ */
+
+static struct tr2_dst tr2dst_perf   = { "GIT_TR2_PERF", 0, 0, 0 };
+
+/*
+ * Set this environment variable to true to omit the "<time> <file>:<line>"
+ * fields from each line written to the builtin performance target.
+ *
+ * Unit tests may want to use this to help with testing.
+ */
+#define GIT_TR2_PERF_BARE "GIT_TR2_BARE"
+static int tr2env_perf_bare;
+
+#define TR2FMT_PERF_FL_WIDTH       (50)
+#define TR2FMT_PERF_MAX_EVENT_NAME (12)
+#define TR2FMT_PERF_REPO_WIDTH     (4)
+#define TR2FMT_PERF_CATEGORY_WIDTH (10)
+
+#define TR2_DOTS_BUFFER_SIZE (100)
+#define TR2_INDENT (2)
+#define TR2_INDENT_LENGTH(ctx) (((ctx)->nr_open_regions - 1) * TR2_INDENT)
+
+static struct strbuf dots = STRBUF_INIT;
+
+static int fn_init(void)
+{
+	int want = tr2_dst_trace_want(&tr2dst_perf);
+	int want_bare;
+	char *bare;
+
+	if (!want)
+		return want;
+
+	strbuf_addchars(&dots, '.', TR2_DOTS_BUFFER_SIZE);
+
+	bare = getenv(GIT_TR2_PERF_BARE);
+	if (bare && *bare &&
+	    ((want_bare = git_parse_maybe_bool(bare)) != -1))
+		tr2env_perf_bare = want_bare;
+
+	return want;
+}
+
+static void fn_term(void)
+{
+	tr2_dst_trace_disable(&tr2dst_perf);
+
+	strbuf_release(&dots);
+}
+
+/*
+ * Format trace line prefix in human-readable classic format for
+ * the performance target:
+ *     "[<time> [<file>:<line>] <bar> <nr_parents> <bar>]
+ *         <thread_name> <bar> <event_name> <bar> [<repo>] <bar>
+ *         [<elapsed_absolute>] [<elapsed_relative>] <bar>
+ *         [<category>] <bar> [<dots>] "
+ */
+static void perf_fmt_prepare(
+	const char *event_name, struct tr2tls_thread_ctx *ctx,
+	const char *file, int line, const struct repository *repo,
+	uint64_t *p_us_elapsed_absolute, uint64_t *p_us_elapsed_relative,
+	const char *category, struct strbuf *buf)
+{
+	int len;
+
+	strbuf_setlen(buf,0);
+
+	if (!tr2env_perf_bare) {
+
+		struct tr2_tbuf tb_now;
+
+		tr2_tbuf_current_time(&tb_now);
+		strbuf_addstr(buf, tb_now.buf);
+		strbuf_addch(buf, ' ');
+
+		if (file && *file)
+			strbuf_addf(buf, "%s:%d ", file, line);
+		while (buf->len < TR2FMT_PERF_FL_WIDTH)
+			strbuf_addch(buf, ' ');
+
+		strbuf_addf(buf, "| d%d | ", tr2_sid_depth());
+	}
+
+	strbuf_addf(buf, "%-*s | %-*s | ",
+		    TR2_MAX_THREAD_NAME, ctx->thread_name.buf,
+		    TR2FMT_PERF_MAX_EVENT_NAME, event_name);
+
+	len = buf->len + TR2FMT_PERF_REPO_WIDTH;
+	if (repo)
+		strbuf_addf(buf, "r%d ", repo->trace2_repo_id);
+	while (buf->len < len)
+		strbuf_addch(buf, ' ' );
+	strbuf_addstr(buf, "| ");
+
+	if (p_us_elapsed_absolute)
+		strbuf_addf(buf, "%9.6f | ",
+			    ((double)(*p_us_elapsed_absolute)) / 1000000.0);
+	else
+		strbuf_addf(buf, "%9s | ", " ");
+
+	if (p_us_elapsed_relative)
+		strbuf_addf(buf, "%9.6f | ",
+			    ((double)(*p_us_elapsed_relative)) / 1000000.0);
+	else
+		strbuf_addf(buf, "%9s | ", " ");
+		
+	strbuf_addf(buf, "%-*s | ", TR2FMT_PERF_CATEGORY_WIDTH,
+		    (category ? category : ""));
+
+	if (ctx->nr_open_regions > 0) {
+		int len_indent = TR2_INDENT_LENGTH(ctx);
+		while (len_indent > dots.len) {
+			strbuf_addf(buf, "%s", dots.buf);
+			len_indent -= dots.len;
+		}
+		strbuf_addf(buf, "%.*s", len_indent, dots.buf);
+	}
+}
+
+static void perf_io_write_fl(
+	const char *file, int line,
+	const char *event_name,
+	const struct repository *repo,
+	uint64_t *p_us_elapsed_absolute,
+	uint64_t *p_us_elapsed_relative,
+	const char *category,
+	const struct strbuf *buf_payload)
+{
+	struct tr2tls_thread_ctx *ctx = tr2tls_get_self();
+	struct strbuf buf_line = STRBUF_INIT;
+
+	perf_fmt_prepare(event_name, ctx, file, line, repo,
+			 p_us_elapsed_absolute, p_us_elapsed_relative,
+			 category, &buf_line);
+	strbuf_addbuf(&buf_line, buf_payload);
+	tr2_dst_write_line(&tr2dst_perf, &buf_line);
+	strbuf_release(&buf_line);
+}
+
+static void fn_version_fl(const char *file, int line)
+{
+	const char *event_name = "version";
+	struct strbuf buf_payload = STRBUF_INIT;
+
+	strbuf_addf(&buf_payload, "%s", git_version_string);
+
+	perf_io_write_fl(file, line, event_name, NULL,
+			 NULL, NULL, NULL,
+			 &buf_payload);
+	strbuf_release(&buf_payload);
+}
+
+static void fn_start_fl(const char *file, int line, const char **argv)
+{
+	const char *event_name = "start";
+	struct strbuf buf_payload = STRBUF_INIT;
+
+	sq_quote_argv_pretty(&buf_payload, argv);
+
+	perf_io_write_fl(file, line, event_name, NULL,
+			 NULL, NULL, NULL,
+			 &buf_payload);
+	strbuf_release(&buf_payload);
+}
+
+static void fn_exit_fl(const char *file, int line,
+		       uint64_t us_elapsed_absolute, int code)
+{
+	const char *event_name = "exit";
+	struct strbuf buf_payload = STRBUF_INIT;
+
+	strbuf_addf(&buf_payload, "code:%d", code);
+
+	perf_io_write_fl(file, line, event_name, NULL,
+			 &us_elapsed_absolute, NULL, NULL,
+			 &buf_payload);
+	strbuf_release(&buf_payload);
+}
+
+static void fn_signal(uint64_t us_elapsed_absolute, int signo)
+{
+	const char *event_name = "signal";
+	struct strbuf buf_payload = STRBUF_INIT;
+
+	strbuf_addf(&buf_payload, "signo:%d", signo);
+
+	perf_io_write_fl(__FILE__, __LINE__, event_name, NULL,
+			 &us_elapsed_absolute, NULL, NULL,
+			 &buf_payload);
+	strbuf_release(&buf_payload);
+}
+
+static void fn_atexit(uint64_t us_elapsed_absolute, int code)
+{
+	const char *event_name = "atexit";
+	struct strbuf buf_payload = STRBUF_INIT;
+
+	strbuf_addf(&buf_payload, "code:%d", code);
+
+	perf_io_write_fl(__FILE__, __LINE__, event_name, NULL,
+			 &us_elapsed_absolute, NULL, NULL,
+			 &buf_payload);
+	strbuf_release(&buf_payload);
+}
+
+static void maybe_append_string_va(struct strbuf *buf,
+				   const char *fmt, va_list ap)
+{
+	if (fmt && *fmt && ap) {
+		va_list copy_ap;
+
+		va_copy(copy_ap, ap);
+		strbuf_vaddf(buf, fmt, copy_ap);
+		va_end(copy_ap);
+		return;
+	}
+
+	if (fmt && *fmt) {
+		strbuf_addstr(buf, fmt);
+		return;
+	}
+}
+
+static void fn_error_va_fl(const char *file, int line,
+			   const char *fmt, va_list ap)
+{
+	const char *event_name = "error";
+	struct strbuf buf_payload = STRBUF_INIT;
+
+	maybe_append_string_va(&buf_payload, fmt, ap);
+
+	perf_io_write_fl(file, line, event_name, NULL,
+			 NULL, NULL, NULL,
+			 &buf_payload);
+	strbuf_release(&buf_payload);
+}
+
+static void fn_command_path_fl(const char *file, int line,
+			       const char *pathname)
+{
+	const char *event_name = "cmd_path";
+	struct strbuf buf_payload = STRBUF_INIT;
+
+	strbuf_addstr(&buf_payload, pathname);
+
+	perf_io_write_fl(file, line, event_name, NULL,
+			 NULL, NULL, NULL,
+			 &buf_payload);
+	strbuf_release(&buf_payload);
+}
+
+static void fn_command_verb_fl(const char *file, int line,
+			       const char *command_verb)
+{
+	const char *event_name = "cmd_verb";
+	struct strbuf buf_payload = STRBUF_INIT;
+
+	strbuf_addstr(&buf_payload, command_verb);
+
+	perf_io_write_fl(file, line, event_name, NULL,
+			 NULL, NULL, NULL,
+			 &buf_payload);
+	strbuf_release(&buf_payload);
+}
+
+static void fn_alias_fl(const char *file, int line, const char *alias,
+			const char **argv)
+{
+	const char *event_name = "alias";
+	struct strbuf buf_payload = STRBUF_INIT;
+
+	strbuf_addf(&buf_payload, "alias:%s argv:", alias);
+	sq_quote_argv_pretty(&buf_payload, argv);
+
+	perf_io_write_fl(file, line, event_name, NULL,
+			 NULL, NULL, NULL,
+			 &buf_payload);
+	strbuf_release(&buf_payload);
+}
+
+static void fn_child_start_fl(const char *file, int line,
+			      uint64_t us_elapsed_absolute,
+			      const struct child_process *cmd)
+{
+	const char *event_name = "child_start";
+	struct strbuf buf_payload = STRBUF_INIT;
+	const char *child_class = ((cmd->trace2_child_class) ?
+				   cmd->trace2_child_class : "?");
+
+	strbuf_addf(&buf_payload, "[ch%d] class:%s",
+		    cmd->trace2_child_id, child_class);
+
+	if (cmd->dir) {
+		strbuf_addstr(&buf_payload, " cd:");
+		sq_quote_buf_pretty(&buf_payload, cmd->dir);
+	}
+
+	strbuf_addstr(&buf_payload, " argv:");
+	if (cmd->git_cmd)
+		strbuf_addstr(&buf_payload, " git");
+	sq_quote_argv_pretty(&buf_payload, cmd->argv);
+
+	perf_io_write_fl(file, line, event_name, NULL,
+			 &us_elapsed_absolute, NULL, NULL,
+			 &buf_payload);
+	strbuf_release(&buf_payload);
+}
+
+static void fn_child_exit_fl(const char *file, int line,
+			     uint64_t us_elapsed_absolute,
+			     int cid, int code, uint64_t us_elapsed_child)
+{
+	const char *event_name = "child_exit";
+	struct strbuf buf_payload = STRBUF_INIT;
+
+	strbuf_addf(&buf_payload, "[ch%d] code:%d", cid, code);
+
+	perf_io_write_fl(file, line, event_name, NULL,
+			 &us_elapsed_absolute, &us_elapsed_child, NULL,
+			 &buf_payload);
+	strbuf_release(&buf_payload);
+}
+
+static void fn_thread_start_fl(const char *file, int line,
+				     uint64_t us_elapsed_absolute)
+{
+	const char *event_name = "thread_start";
+	struct strbuf buf_payload = STRBUF_INIT;
+
+	perf_io_write_fl(file, line, event_name, NULL,
+			 &us_elapsed_absolute, NULL, NULL,
+			 &buf_payload);
+	strbuf_release(&buf_payload);
+}
+
+static void fn_thread_exit_fl(const char *file, int line,
+			      uint64_t us_elapsed_absolute,
+			      uint64_t us_elapsed_thread)
+{
+	const char *event_name = "thread_exit";
+	struct strbuf buf_payload = STRBUF_INIT;
+
+	perf_io_write_fl(file, line, event_name, NULL,
+			 &us_elapsed_absolute, &us_elapsed_thread, NULL,
+			 &buf_payload);
+	strbuf_release(&buf_payload);
+}
+
+static void fn_exec_fl(const char *file, int line,
+		       uint64_t us_elapsed_absolute,
+		       const char *exe, const char **argv)
+{
+	const char *event_name = "exec";
+	struct strbuf buf_payload = STRBUF_INIT;
+
+	strbuf_addstr(&buf_payload, "argv:");
+	if (exe)
+		strbuf_addf(&buf_payload, " %s", exe);
+	sq_quote_argv_pretty(&buf_payload, argv);
+
+	perf_io_write_fl(file, line, event_name, NULL,
+			 &us_elapsed_absolute, NULL, NULL,
+			 &buf_payload);
+	strbuf_release(&buf_payload);
+}
+
+static void fn_exec_result_fl(const char *file, int line,
+			      uint64_t us_elapsed_absolute,
+			      int code)
+{
+	const char *event_name = "exec_result";
+	struct strbuf buf_payload = STRBUF_INIT;
+
+	strbuf_addf(&buf_payload, "code:%d", code);
+	if (code > 0)
+		strbuf_addf(&buf_payload, " err:%s", strerror(code));
+
+	perf_io_write_fl(file, line, event_name, NULL,
+			 &us_elapsed_absolute, NULL, NULL,
+			 &buf_payload);
+	strbuf_release(&buf_payload);
+}
+
+static void fn_param_fl(const char *file, int line,
+			const char *param, const char *value)
+{
+	const char *event_name = "def_param";
+	struct strbuf buf_payload = STRBUF_INIT;
+
+	strbuf_addf(&buf_payload, "%s:%s", param, value);
+
+	perf_io_write_fl(file, line, event_name, NULL,
+			 NULL, NULL, NULL,
+			 &buf_payload);
+	strbuf_release(&buf_payload);
+}
+
+static void fn_repo_fl(const char *file, int line,
+		       const struct repository *repo)
+{
+	const char *event_name = "def_repo";
+	struct strbuf buf_payload = STRBUF_INIT;
+
+	strbuf_addstr(&buf_payload, "worktree:");
+	sq_quote_buf_pretty(&buf_payload, repo->worktree);
+
+	perf_io_write_fl(file, line, event_name, repo,
+			 NULL, NULL, NULL,
+			 &buf_payload);
+	strbuf_release(&buf_payload);
+}
+
+static void fn_region_enter_printf_va_fl(const char *file, int line,
+					 uint64_t us_elapsed_absolute,
+					 const char *category,
+					 const char *label,
+					 const struct repository *repo,
+					 const char *fmt, va_list ap)
+{
+	const char *event_name = "region_enter";
+	struct strbuf buf_payload = STRBUF_INIT;
+
+	if (label)
+		strbuf_addf(&buf_payload, "label:%s ", label);
+	maybe_append_string_va(&buf_payload, fmt, ap);
+
+	perf_io_write_fl(file, line, event_name, repo,
+			 &us_elapsed_absolute, NULL, category,
+			 &buf_payload);
+	strbuf_release(&buf_payload);
+}
+
+static void fn_region_leave_printf_va_fl(const char *file, int line,
+					 uint64_t us_elapsed_absolute,
+					 uint64_t us_elapsed_region,
+					 const char *category,
+					 const char *label,
+					 const struct repository *repo,
+					 const char *fmt, va_list ap)
+{
+	const char *event_name = "region_leave";
+	struct strbuf buf_payload = STRBUF_INIT;
+
+	if (label)
+		strbuf_addf(&buf_payload, "label:%s ", label);
+	maybe_append_string_va(&buf_payload, fmt, ap);
+
+	perf_io_write_fl(file, line, event_name, repo,
+			 &us_elapsed_absolute, &us_elapsed_region, category,
+			 &buf_payload);
+	strbuf_release(&buf_payload);
+}
+
+static void fn_data_fl(const char *file, int line,
+		       uint64_t us_elapsed_absolute,
+		       uint64_t us_elapsed_region,
+		       const char *category,
+		       const struct repository *repo,
+		       const char *key,
+		       const char *value)
+{
+	const char *event_name = "data";
+	struct strbuf buf_payload = STRBUF_INIT;
+
+	strbuf_addf(&buf_payload, "%s:%s", key, value);
+
+	perf_io_write_fl(file, line, event_name, repo,
+			 &us_elapsed_absolute, &us_elapsed_region, category,
+			 &buf_payload);
+	strbuf_release(&buf_payload);
+}
+
+static void fn_printf_va_fl(const char *file, int line,
+			    uint64_t us_elapsed_absolute,
+			    const char *fmt, va_list ap)
+{
+	const char *event_name = "printf";
+	struct strbuf buf_payload = STRBUF_INIT;
+
+	maybe_append_string_va(&buf_payload, fmt, ap);
+
+	perf_io_write_fl(file, line, event_name, NULL,
+			 &us_elapsed_absolute, NULL, NULL,
+			 &buf_payload);
+	strbuf_release(&buf_payload);
+}
+
+struct tr2_tgt tr2_tgt_perf =
+{
+	&tr2dst_perf,
+
+	fn_init,
+	fn_term,
+
+	fn_version_fl,
+	fn_start_fl,
+	fn_exit_fl,
+	fn_signal,
+	fn_atexit,
+	fn_error_va_fl,
+	fn_command_path_fl,
+	fn_command_verb_fl,
+	fn_alias_fl,
+	fn_child_start_fl,
+	fn_child_exit_fl,
+	fn_thread_start_fl,
+	fn_thread_exit_fl,
+	fn_exec_fl,
+	fn_exec_result_fl,
+	fn_param_fl,
+	fn_repo_fl,
+	fn_region_enter_printf_va_fl,
+	fn_region_leave_printf_va_fl,
+	fn_data_fl,
+	fn_printf_va_fl,
+};
diff --git a/trace2/tr2_tls.c b/trace2/tr2_tls.c
new file mode 100644
index 00000000000000..4d5747951e5e43
--- /dev/null
+++ b/trace2/tr2_tls.c
@@ -0,0 +1,170 @@
+#include "cache.h"
+#include "thread-utils.h"
+#include "trace2/tr2_tls.h"
+
+/*
+ * This file contains "private/protected" routines for TRACE2.
+ */
+
+/*
+ * Initialize size of the thread stack for nested regions.
+ * This is used to store nested region start times.  Note that
+ * this stack is per-thread and not per-trace-key.
+ */
+#define TR2_REGION_NESTING_INITIAL_SIZE (100)
+
+static struct tr2tls_thread_ctx *tr2tls_thread_main;
+static uint64_t tr2tls_us_start_main;
+
+static pthread_mutex_t tr2tls_mutex;
+static pthread_key_t tr2tls_key;
+
+static int tr2_next_thread_id; /* modify under lock */
+
+struct tr2tls_thread_ctx *tr2tls_create_self(const char *thread_name)
+{
+	uint64_t us_now = getnanotime() / 1000;
+	struct tr2tls_thread_ctx *ctx = xcalloc(1, sizeof(*ctx));
+
+	/*
+	 * Implicitly "tr2tls_push_self()" to capture the thread's start
+	 * time in array_us_start[0].  For the main thread this gives us the
+	 * application run time.
+	 */
+	ctx->alloc = TR2_REGION_NESTING_INITIAL_SIZE;
+	ctx->array_us_start = (uint64_t*)xcalloc(ctx->alloc, sizeof(uint64_t));
+	ctx->array_us_start[ctx->nr_open_regions++] = us_now;
+
+	ctx->thread_id = tr2tls_locked_increment(&tr2_next_thread_id);
+	
+	strbuf_init(&ctx->thread_name, 0);
+	if (ctx->thread_id)
+		strbuf_addf(&ctx->thread_name, "th%02d:", ctx->thread_id);
+	strbuf_addstr(&ctx->thread_name, thread_name);
+	if (ctx->thread_name.len > TR2_MAX_THREAD_NAME)
+		strbuf_setlen(&ctx->thread_name, TR2_MAX_THREAD_NAME);
+
+	pthread_setspecific(tr2tls_key, ctx);
+
+	return ctx;
+}
+
+struct tr2tls_thread_ctx *tr2tls_get_self(void)
+{
+	struct tr2tls_thread_ctx * ctx = pthread_getspecific(tr2tls_key);
+
+	/*
+	 * If the thread-proc did not call trace2_thread_start(), we won't
+	 * have any TLS data associated with the current thread.  Fix it
+	 * here and silently continue.
+	 */
+	if (!ctx)
+		ctx = tr2tls_create_self("unknown");
+
+	return ctx;
+}
+
+int tr2tls_is_main_thread(void)
+{
+	struct tr2tls_thread_ctx * ctx;
+
+	ctx = tr2tls_get_self();
+
+	return ctx == tr2tls_thread_main;
+}
+
+void tr2tls_unset_self(void)
+{
+	struct tr2tls_thread_ctx * ctx;
+
+	ctx = tr2tls_get_self();
+
+	pthread_setspecific(tr2tls_key, NULL);
+
+	free(ctx->array_us_start);
+	free(ctx);
+}
+
+void tr2tls_push_self(uint64_t us_now)
+{
+	struct tr2tls_thread_ctx *ctx = tr2tls_get_self();
+
+	ALLOC_GROW(ctx->array_us_start, ctx->nr_open_regions + 1, ctx->alloc);
+	ctx->array_us_start[ctx->nr_open_regions++] = us_now;
+}
+
+void tr2tls_pop_self(void)
+{
+	struct tr2tls_thread_ctx *ctx = tr2tls_get_self();
+
+	if (!ctx->nr_open_regions)
+		BUG("no open regions in thread '%s'", ctx->thread_name.buf);
+
+	ctx->nr_open_regions--;
+}
+
+void tr2tls_pop_unwind_self(void)
+{
+	struct tr2tls_thread_ctx *ctx = tr2tls_get_self();
+
+	while (ctx->nr_open_regions > 1)
+		tr2tls_pop_self();
+}
+
+uint64_t tr2tls_region_elasped_self(uint64_t us)
+{
+	struct tr2tls_thread_ctx *ctx;
+	uint64_t us_start;
+
+	ctx = tr2tls_get_self();
+	if (!ctx->nr_open_regions)
+		return 0;
+	
+	us_start = ctx->array_us_start[ctx->nr_open_regions - 1];
+
+	return us - us_start;
+}
+
+uint64_t tr2tls_absolute_elapsed(uint64_t us)
+{
+	if (!tr2tls_thread_main)
+		return 0;
+
+	return us - tr2tls_us_start_main;
+}
+
+void tr2tls_init(void)
+{
+	pthread_key_create(&tr2tls_key, NULL);
+	init_recursive_mutex(&tr2tls_mutex);
+
+	tr2tls_thread_main = tr2tls_create_self("main");
+	/*
+	 * Keep a copy of the absolute start time of the main thread
+	 * in a fixed variable since other threads need to access it.
+	 * This also eliminates the need to lock accesses to the main
+	 * thread's array (because of reallocs).
+	 */
+	tr2tls_us_start_main = tr2tls_thread_main->array_us_start[0];
+}
+
+void tr2tls_release(void)
+{
+	tr2tls_unset_self();
+	tr2tls_thread_main = NULL;
+
+	pthread_mutex_destroy(&tr2tls_mutex);
+	pthread_key_delete(tr2tls_key);
+}
+
+int tr2tls_locked_increment(int *p)
+{
+	int current_value;
+
+	pthread_mutex_lock(&tr2tls_mutex);
+	current_value = *p;
+	*p = current_value + 1;
+	pthread_mutex_unlock(&tr2tls_mutex);
+
+	return current_value;
+}
diff --git a/trace2/tr2_tls.h b/trace2/tr2_tls.h
new file mode 100644
index 00000000000000..145fa7e462ed77
--- /dev/null
+++ b/trace2/tr2_tls.h
@@ -0,0 +1,99 @@
+#ifndef TR2_TLS_H
+#define TR2_TLS_H
+
+/*
+ * This file contains "private/protected" declarations for TRACE2.
+ */
+
+/*
+ * Arbitry limit for thread names for column alignment.
+ */
+#define TR2_MAX_THREAD_NAME (24)
+
+struct tr2tls_thread_ctx {
+	struct strbuf thread_name;
+	uint64_t *array_us_start;
+	int alloc;
+	int nr_open_regions; /* plays role of "nr" in ALLOC_GROW */
+	int thread_id;
+};
+
+/*
+ * Create TLS data for the current thread.  This gives us a place to
+ * put per-thread data, such as thread start time, function nesting
+ * and a per-thread label for our messages.
+ *
+ * We assume the first thread is "main".  Other threads are given
+ * non-zero thread-ids to help distinguish messages from concurrent
+ * threads.
+ *
+ * Truncate the thread name if necessary to help with column alignment
+ * in printf-style messages.
+ *
+ * In this and all following functions the term "self" refers to the
+ * current thread.
+ */
+struct tr2tls_thread_ctx *tr2tls_create_self(const char *thread_name);
+
+/*
+ * Get our TLS data.
+ */
+struct tr2tls_thread_ctx *tr2tls_get_self(void);
+
+/*
+ * return true if the current thread is the main thread.
+ */
+int tr2tls_is_main_thread(void);
+
+/*
+ * Free our TLS data.
+ */
+void tr2tls_unset_self(void);
+
+/*
+ * Begin a new nested region and remember the start time.
+ */
+void tr2tls_push_self(uint64_t us_now);
+
+/*
+ * End the innermost nested region.
+ */
+void tr2tls_pop_self(void);
+
+/*
+ * Pop any extra (above the first) open regions on the current
+ * thread and discard.  During a thread-exit, we should only
+ * have region[0] that was pushed in trace2_thread_start() if
+ * the thread exits normally.
+ */
+void tr2tls_pop_unwind_self(void);
+
+/*
+ * Compute the elapsed time since the innermost region in the
+ * current thread started and the given time (usually now).
+ */
+uint64_t tr2tls_region_elasped_self(uint64_t us);
+
+/*
+ * Compute the elapsed time since the main thread started
+ * and the given time (usually now).  This is assumed to
+ * be the absolute run time of the process.
+ */
+uint64_t tr2tls_absolute_elapsed(uint64_t us);
+
+/*
+ * Initialize the tr2 TLS system.
+ */
+void tr2tls_init(void);
+
+/*
+ * Free all tr2 TLS resources.
+ */
+void tr2tls_release(void);
+
+/*
+ * Protected increment of an integer.
+ */
+int tr2tls_locked_increment(int *p);
+
+#endif /* TR2_TLS_H */
diff --git a/transport-helper.c b/transport-helper.c
index 35199e50a03e95..fa78a8788568ab 100644
--- a/transport-helper.c
+++ b/transport-helper.c
@@ -129,6 +129,8 @@ static struct child_process *get_helper(struct transport *transport)
 		argv_array_pushf(&helper->env_array, "%s=%s",
 				 GIT_DIR_ENVIRONMENT, get_git_dir());
 
+	helper->trace2_child_class = helper->args.argv[0]; /* "remote-<name>" */
+
 	code = start_command(helper);
 	if (code < 0 && errno == ENOENT)
 		die(_("unable to find remote helper for '%s'"), data->name);
diff --git a/unpack-trees.c b/unpack-trees.c
index 7570df481bf698..b139c5656f8319 100644
--- a/unpack-trees.c
+++ b/unpack-trees.c
@@ -18,6 +18,8 @@
 #include "fsmonitor.h"
 #include "object-store.h"
 #include "fetch-object.h"
+#include "gvfs.h"
+#include "virtualfilesystem.h"
 
 /*
  * Error messages expected by scripts out of plumbing commands such as
@@ -522,7 +524,9 @@ static int apply_sparse_checkout(struct index_state *istate,
 		 */
 		if (!(ce->ce_flags & CE_UPDATE) && verify_uptodate_sparse(ce, o))
 			return -1;
-		ce->ce_flags |= CE_WT_REMOVE;
+		if (!gvfs_config_is_set(GVFS_NO_DELETE_OUTSIDE_SPARSECHECKOUT))
+			ce->ce_flags |= CE_WT_REMOVE;
+
 		ce->ce_flags &= ~CE_UPDATE;
 	}
 	if (was_skip_worktree && !ce_skip_worktree(ce)) {
@@ -1363,6 +1367,14 @@ static int clear_ce_flags_1(struct index_state *istate,
 			continue;
 		}
 
+		/* if it's not in the virtual file system, exit early */
+		if (core_virtualfilesystem) {
+			if (is_included_in_virtualfilesystem(ce->name, ce->ce_namelen) > 0)
+				ce->ce_flags &= ~clear_mask;
+			cache++;
+			continue;
+		}
+
 		if (prefix->len && strncmp(ce->name, prefix->buf, prefix->len))
 			break;
 
@@ -1481,12 +1493,16 @@ int unpack_trees(unsigned len, struct tree_desc *t, struct unpack_trees_options
 	if (!core_apply_sparse_checkout || !o->update)
 		o->skip_sparse_checkout = 1;
 	if (!o->skip_sparse_checkout) {
-		char *sparse = git_pathdup("info/sparse-checkout");
-		if (add_excludes_from_file_to_list(sparse, "", 0, &el, NULL) < 0)
-			o->skip_sparse_checkout = 1;
-		else
+		if (core_virtualfilesystem) {
 			o->el = &el;
-		free(sparse);
+		} else {
+			char *sparse = git_pathdup("info/sparse-checkout");
+			if (add_excludes_from_file_to_list(sparse, "", 0, &el, NULL) < 0)
+				o->skip_sparse_checkout = 1;
+			else
+				o->el = &el;
+			free(sparse);
+		}
 	}
 
 	memset(&o->result, 0, sizeof(o->result));
@@ -1578,7 +1594,7 @@ int unpack_trees(unsigned len, struct tree_desc *t, struct unpack_trees_options
 
 		/*
 		 * Sparse checkout loop #2: set NEW_SKIP_WORKTREE on entries not in loop #1
-		 * If the will have NEW_SKIP_WORKTREE, also set CE_SKIP_WORKTREE
+		 * If they will have NEW_SKIP_WORKTREE, also set CE_SKIP_WORKTREE
 		 * so apply_sparse_checkout() won't attempt to remove it from worktree
 		 */
 		mark_new_skip_worktree(o->el, &o->result, CE_ADDED, CE_SKIP_WORKTREE | CE_NEW_SKIP_WORKTREE);
@@ -1638,6 +1654,8 @@ int unpack_trees(unsigned len, struct tree_desc *t, struct unpack_trees_options
 						  WRITE_TREE_SILENT |
 						  WRITE_TREE_REPAIR);
 		}
+
+		o->result.updated_workdir = 1;
 		discard_index(o->dst_index);
 		*o->dst_index = o->result;
 	} else {
@@ -2089,6 +2107,27 @@ static int deleted_entry(const struct cache_entry *ce,
 	}
 	if (!(old->ce_flags & CE_CONFLICTED) && verify_uptodate(old, o))
 		return -1;
+
+	/*
+	 * When marking entries to remove from the index and the working
+	 * directory this option will take into account what the
+	 * skip-worktree bit was set to so that if the entry has the
+	 * skip-worktree bit set it will not be removed from the working
+	 * directory.  This will allow virtualized working directories to
+	 * detect the change to HEAD and use the new commit tree to show
+	 * the files that are in the working directory.
+	 *
+	 * old is the cache_entry that will have the skip-worktree bit set
+	 * which will need to be preserved when the CE_REMOVE entry is added
+	 */
+	if (gvfs_config_is_set(GVFS_NO_DELETE_OUTSIDE_SPARSECHECKOUT) &&
+		old &&
+		old->ce_flags & CE_SKIP_WORKTREE) {
+		add_entry(o, old, CE_REMOVE, 0);
+		invalidate_ce_path(old, o);
+		return 1;
+	}
+
 	add_entry(o, ce, CE_REMOVE, 0);
 	invalidate_ce_path(ce, o);
 	return 1;
diff --git a/usage.c b/usage.c
index cc803336bd5e67..3f57bac0d52387 100644
--- a/usage.c
+++ b/usage.c
@@ -22,17 +22,48 @@ void vreportf(const char *prefix, const char *err, va_list params)
 static NORETURN void usage_builtin(const char *err, va_list params)
 {
 	vreportf("usage: ", err, params);
+
+	/*
+	 * For command instances where we detected a syntax *before* the
+	 * command dispatch in cmd_main(), we don't know what verb to
+	 * report.  Force it to "_usage_" to facilitate post-processing.
+	 */
+	trace2_cmd_verb("_usage_");
+
+	/*
+	 * Currently, the (err, params) are usually just the static usage
+	 * string which isn't very useful here.  Usually, the call site
+	 * manually calls fprintf(stderr,...) with the actual detailed
+	 * syntax error before calling usage().
+	 *
+	 * TODO It would be nice to update the call sites to pass both
+	 * the static usage string and the detailed error message.
+	 */
+
 	exit(129);
 }
 
 static NORETURN void die_builtin(const char *err, va_list params)
 {
+	/*
+	 * We call this trace2 function first and expect it to va_copy 'params'
+	 * before using it (because an 'ap' can only be walked once).
+	 */
+	trace2_cmd_error_va(err, params);
+
 	vreportf("fatal: ", err, params);
+
 	exit(128);
 }
 
 static void error_builtin(const char *err, va_list params)
 {
+	/*
+	 * We call this trace2 function first and expect it to va_copy 'params'
+	 * before using it (because an 'ap' can only be walked once).
+	 */
+	trace2_cmd_error_va(err, params);
+
 	vreportf("error: ", err, params);
 }
 
diff --git a/virtualfilesystem.c b/virtualfilesystem.c
new file mode 100644
index 00000000000000..424680b4374530
--- /dev/null
+++ b/virtualfilesystem.c
@@ -0,0 +1,308 @@
+#include "cache.h"
+#include "config.h"
+#include "dir.h"
+#include "hashmap.h"
+#include "run-command.h"
+#include "virtualfilesystem.h"
+
+#define HOOK_INTERFACE_VERSION	(1)
+
+static struct strbuf virtual_filesystem_data = STRBUF_INIT;
+static struct hashmap virtual_filesystem_hashmap;
+static struct hashmap parent_directory_hashmap;
+
+struct virtualfilesystem {
+	struct hashmap_entry ent; /* must be the first member! */
+	const char *pattern;
+	int patternlen;
+};
+
+static unsigned int(*vfshash)(const void *buf, size_t len);
+static int(*vfscmp)(const char *a, const char *b, size_t len);
+
+static int vfs_hashmap_cmp(const void *unused_cmp_data,
+	const void *a, const void *b, const void *key)
+{
+	const struct virtualfilesystem *vfs1 = a;
+	const struct virtualfilesystem *vfs2 = b;
+
+	return vfscmp(vfs1->pattern, vfs2->pattern, vfs1->patternlen);
+}
+
+static void get_virtual_filesystem_data(struct strbuf *vfs_data)
+{
+	struct child_process cp = CHILD_PROCESS_INIT;
+	int err;
+
+	strbuf_init(vfs_data, 0);
+
+	argv_array_push(&cp.args, core_virtualfilesystem);
+	argv_array_pushf(&cp.args, "%d", HOOK_INTERFACE_VERSION);
+	cp.use_shell = 1;
+	cp.dir = get_git_work_tree();
+
+	err = capture_command(&cp, vfs_data, 1024);
+	if (err)
+		die("unable to load virtual file system");
+}
+
+static int check_includes_hashmap(struct hashmap *map, const char *pattern, int patternlen)
+{
+	struct strbuf sb = STRBUF_INIT;
+	struct virtualfilesystem vfs;
+	char *slash;
+
+	/* Check straight mapping */
+	strbuf_reset(&sb);
+	strbuf_add(&sb, pattern, patternlen);
+	vfs.pattern = sb.buf;
+	vfs.patternlen = sb.len;
+	hashmap_entry_init(&vfs, vfshash(vfs.pattern, vfs.patternlen));
+	if (hashmap_get(map, &vfs, NULL)) {
+		strbuf_release(&sb);
+		return 1;
+	}
+
+	/*
+	 * Check to see if it matches a directory or any path
+	 * underneath it.  In other words, 'a/b/foo.txt' will match
+	 * '/', 'a/', and 'a/b/'.
+	 */
+	slash = strchr(sb.buf, '/');
+	while (slash) {
+		vfs.pattern = sb.buf;
+		vfs.patternlen = slash - sb.buf + 1;
+		hashmap_entry_init(&vfs, vfshash(vfs.pattern, vfs.patternlen));
+		if (hashmap_get(map, &vfs, NULL)) {
+			strbuf_release(&sb);
+			return 1;
+		}
+		slash = strchr(slash + 1, '/');
+	}
+
+	strbuf_release(&sb);
+	return 0;
+}
+
+static void includes_hashmap_add(struct hashmap *map, const char *pattern, const int patternlen)
+{
+	struct virtualfilesystem *vfs;
+
+	vfs = xmalloc(sizeof(struct virtualfilesystem));
+	vfs->pattern = pattern;
+	vfs->patternlen = patternlen;
+	hashmap_entry_init(vfs, vfshash(vfs->pattern, vfs->patternlen));
+	hashmap_add(map, vfs);
+}
+
+static void initialize_includes_hashmap(struct hashmap *map, struct strbuf *vfs_data)
+{
+	char *buf, *entry;
+	size_t len;
+	int i;
+
+	/*
+	 * Build a hashmap of the virtual file system data we can use to look
+	 * for cache entry matches quickly
+	 */
+	vfshash = ignore_case ? memihash : memhash;
+	vfscmp = ignore_case ? strncasecmp : strncmp;
+	hashmap_init(map, vfs_hashmap_cmp, NULL, 0);
+
+	entry = buf = vfs_data->buf;
+	len = vfs_data->len;
+	for (i = 0; i < len; i++) {
+		if (buf[i] == '\0') {
+			includes_hashmap_add(map, entry, buf + i - entry);
+			entry = buf + i + 1;
+		}
+	}
+}
+
+/*
+ * Return 1 if the requested item is found in the virtual file system,
+ * 0 for not found and -1 for undecided.
+ */
+int is_included_in_virtualfilesystem(const char *pathname, int pathlen)
+{
+	if (!core_virtualfilesystem)
+		return -1;
+
+	if (!virtual_filesystem_hashmap.tablesize && virtual_filesystem_data.len)
+		initialize_includes_hashmap(&virtual_filesystem_hashmap, &virtual_filesystem_data);
+	if (!virtual_filesystem_hashmap.tablesize)
+		return -1;
+	
+	return check_includes_hashmap(&virtual_filesystem_hashmap, pathname, pathlen);
+}
+
+static void parent_directory_hashmap_add(struct hashmap *map, const char *pattern, const int patternlen)
+{
+	char *slash;
+	struct virtualfilesystem *vfs;
+
+	/*
+	 * Add any directories leading up to the file as the excludes logic
+	 * needs to match directories leading up to the files as well. Detect
+	 * and prevent unnecessary duplicate entries which will be common.
+	 */
+	if (patternlen > 1) {
+		slash = strchr(pattern + 1, '/');
+		while (slash) {
+			vfs = xmalloc(sizeof(struct virtualfilesystem));
+			vfs->pattern = pattern;
+			vfs->patternlen = slash - pattern + 1;
+			hashmap_entry_init(vfs, vfshash(vfs->pattern, vfs->patternlen));
+			if (hashmap_get(map, vfs, NULL))
+				free(vfs);
+			else
+				hashmap_add(map, vfs);
+			slash = strchr(slash + 1, '/');
+		}
+	}
+}
+
+static void initialize_parent_directory_hashmap(struct hashmap *map, struct strbuf *vfs_data)
+{
+	char *buf, *entry;
+	size_t len;
+	int i;
+
+	/*
+	 * Build a hashmap of the parent directories contained in the virtual
+	 * file system data we can use to look for matches quickly
+	 */
+	vfshash = ignore_case ? memihash : memhash;
+	vfscmp = ignore_case ? strncasecmp : strncmp;
+	hashmap_init(map, vfs_hashmap_cmp, NULL, 0);
+
+	entry = buf = vfs_data->buf;
+	len = vfs_data->len;
+	for (i = 0; i < len; i++) {
+		if (buf[i] == '\0') {
+			parent_directory_hashmap_add(map, entry, buf + i - entry);
+			entry = buf + i + 1;
+		}
+	}
+}
+
+static int check_directory_hashmap(struct hashmap *map, const char *pathname, int pathlen)
+{
+	struct strbuf sb = STRBUF_INIT;
+	struct virtualfilesystem vfs;
+
+	/* Check for directory */
+	strbuf_reset(&sb);
+	strbuf_add(&sb, pathname, pathlen);
+	strbuf_addch(&sb, '/');
+	vfs.pattern = sb.buf;
+	vfs.patternlen = sb.len;
+	hashmap_entry_init(&vfs, vfshash(vfs.pattern, vfs.patternlen));
+	if (hashmap_get(map, &vfs, NULL)) {
+		strbuf_release(&sb);
+		return 0;
+	}
+
+	strbuf_release(&sb);
+	return 1;
+}
+
+/*
+ * Return 1 for exclude, 0 for include and -1 for undecided.
+ */
+int is_excluded_from_virtualfilesystem(const char *pathname, int pathlen, int dtype)
+{
+	if (!core_virtualfilesystem)
+		return -1;
+
+	if (dtype != DT_REG && dtype != DT_DIR && dtype != DT_LNK)
+		die(_("is_excluded_from_virtualfilesystem passed unhandled dtype"));
+
+	if (dtype == DT_REG || dtype == DT_LNK) {
+		int ret = is_included_in_virtualfilesystem(pathname, pathlen);
+		if (ret > 0)
+			return 0;
+		if (ret == 0)
+			return 1;
+		return ret;
+	}
+
+	if (dtype == DT_DIR) {
+		int ret = is_included_in_virtualfilesystem(pathname, pathlen);
+		if (ret > 0)
+			return 0;
+
+		if (!parent_directory_hashmap.tablesize && virtual_filesystem_data.len)
+			initialize_parent_directory_hashmap(&parent_directory_hashmap, &virtual_filesystem_data);
+		if (!parent_directory_hashmap.tablesize)
+			return -1;
+
+		return check_directory_hashmap(&parent_directory_hashmap, pathname, pathlen);
+	}
+
+	return -1;
+}
+
+/*
+ * Update the CE_SKIP_WORKTREE bits based on the virtual file system.
+ */
+void apply_virtualfilesystem(struct index_state *istate)
+{
+	char *buf, *entry;
+	int i;
+
+	if (!git_config_get_virtualfilesystem())
+		return;
+
+	if (!virtual_filesystem_data.len)
+		get_virtual_filesystem_data(&virtual_filesystem_data);
+
+	/* set CE_SKIP_WORKTREE bit on all entries */
+	for (i = 0; i < istate->cache_nr; i++)
+		istate->cache[i]->ce_flags |= CE_SKIP_WORKTREE;
+
+	/* clear CE_SKIP_WORKTREE bit for everything in the virtual file system */
+	entry = buf = virtual_filesystem_data.buf;
+	for (i = 0; i < virtual_filesystem_data.len; i++) {
+		if (buf[i] == '\0') {
+			int pos, len;
+
+			len = buf + i - entry;
+
+			/* look for a directory wild card (ie "dir1/") */
+			if (buf[i - 1] == '/') {
+				if (ignore_case)
+					adjust_dirname_case(istate, entry);
+				pos = index_name_pos(istate, entry, len);
+				if (pos < 0) {
+					pos = -pos - 1;
+					while (pos < istate->cache_nr && !fspathncmp(istate->cache[pos]->name, entry, len)) {
+						istate->cache[pos]->ce_flags &= ~CE_SKIP_WORKTREE;
+						pos++;
+					}
+				}
+			} else {
+				if (ignore_case) {
+					struct cache_entry *ce = index_file_exists(istate, entry, len, ignore_case);
+					if (ce)
+						ce->ce_flags &= ~CE_SKIP_WORKTREE;
+				} else {
+					int pos = index_name_pos(istate, entry, len);
+					if (pos >= 0)
+						istate->cache[pos]->ce_flags &= ~CE_SKIP_WORKTREE;
+				}
+			}
+
+			entry += len + 1;
+		}
+	}
+}
+
+/*
+ * Free the virtual file system data structures.
+ */
+void free_virtualfilesystem(void) {
+	hashmap_free(&virtual_filesystem_hashmap, 1);
+	hashmap_free(&parent_directory_hashmap, 1);
+	strbuf_release(&virtual_filesystem_data);
+}
diff --git a/virtualfilesystem.h b/virtualfilesystem.h
new file mode 100644
index 00000000000000..5e8c5b096df09a
--- /dev/null
+++ b/virtualfilesystem.h
@@ -0,0 +1,25 @@
+#ifndef VIRTUALFILESYSTEM_H
+#define VIRTUALFILESYSTEM_H
+
+/*
+ * Update the CE_SKIP_WORKTREE bits based on the virtual file system.
+ */
+void apply_virtualfilesystem(struct index_state *istate);
+
+/*
+ * Return 1 if the requested item is found in the virtual file system,
+ * 0 for not found and -1 for undecided.
+ */
+int is_included_in_virtualfilesystem(const char *pathname, int pathlen);
+
+/*
+ * Return 1 for exclude, 0 for include and -1 for undecided.
+ */
+int is_excluded_from_virtualfilesystem(const char *pathname, int pathlen, int dtype);
+
+/*
+ * Free the virtual file system data structures.
+ */
+void free_virtualfilesystem(void);
+
+#endif
diff --git a/walker.c b/walker.c
index 96990d84dabfdd..d7583b9b09b41b 100644
--- a/walker.c
+++ b/walker.c
@@ -82,7 +82,8 @@ static int process_commit(struct walker *walker, struct commit *commit)
 		return -1;
 
 	while (complete && complete->item->date >= commit->date) {
-		pop_most_recent_commit(&complete, COMPLETE);
+		pop_most_recent_commit(&complete, COMPLETE,
+				       GENERATION_NUMBER_ZERO);
 	}
 
 	if (commit->object.flags & COMPLETE)
diff --git a/wt-status-deserialize.c b/wt-status-deserialize.c
new file mode 100644
index 00000000000000..8647ed3ab23cbb
--- /dev/null
+++ b/wt-status-deserialize.c
@@ -0,0 +1,822 @@
+#include "cache.h"
+#include "wt-status.h"
+#include "pkt-line.h"
+#include "trace.h"
+
+static struct trace_key trace_deserialize = TRACE_KEY_INIT(DESERIALIZE);
+
+enum deserialize_parse_strategy {
+	DESERIALIZE_STRATEGY_AS_IS,
+	DESERIALIZE_STRATEGY_SKIP,
+	DESERIALIZE_STRATEGY_NORMAL,
+	DESERIALIZE_STRATEGY_ALL
+};
+
+static int check_path_contains(const char *out, int out_len, const char *in, int in_len)
+{
+	return (out_len > 0 &&
+		out_len < in_len &&
+		(out[out_len - 1] == '/') &&
+		!memcmp(out, in, out_len));
+}
+
+static const char *my_packet_read_line(int fd, int *line_len)
+{
+	static char buf[LARGE_PACKET_MAX];
+
+	*line_len = packet_read(fd, NULL, NULL, buf, sizeof(buf),
+				PACKET_READ_CHOMP_NEWLINE |
+				PACKET_READ_GENTLE_ON_EOF);
+	return (*line_len > 0) ? buf : NULL;
+}
+
+/*
+ * mtime_reported contains the mtime of the index when the
+ * serialization snapshot was computed.
+ *
+ * mtime_observed_on_disk contains the mtime of the index now.
+ *
+ * If these 2 times are different, then the .git/index has
+ * changed since the serialization cache was created and we
+ * must reject the cache because anything could have changed.
+ *
+ * If they are the same, we continue trying to use the cache.
+ */
+static int my_validate_index(const struct cache_time *mtime_reported)
+{
+	const char *path = get_index_file();
+	struct stat st;
+	struct cache_time mtime_observed_on_disk;
+
+	if (lstat(path, &st)) {
+		trace_printf_key(&trace_deserialize, "could not stat index");
+		return DESERIALIZE_ERR;
+	}
+	mtime_observed_on_disk.sec = st.st_mtime;
+	mtime_observed_on_disk.nsec = ST_MTIME_NSEC(st);
+	if ((mtime_observed_on_disk.sec != mtime_reported->sec) ||
+	    (mtime_observed_on_disk.nsec != mtime_reported->nsec)) {
+		trace_printf_key(&trace_deserialize,
+				 "index mtime changed [des %d %d][obs %d %d]",
+			     mtime_reported->sec, mtime_reported->nsec,
+			     mtime_observed_on_disk.sec, mtime_observed_on_disk.nsec);
+		return DESERIALIZE_ERR;
+	}
+
+	return DESERIALIZE_OK;
+}
+
+/*
+ * Use the given key and exclude pathname to compute a serialization header
+ * reflecting the current contents on disk.  See if that matches the value
+ * computed for this key when the cache was written.  Reject the cache if
+ * anything has changed.
+ */
+static int my_validate_excludes(const char *path, const char *key, const char *line)
+{
+	struct strbuf sb = STRBUF_INIT;
+	int r;
+
+	wt_serialize_compute_exclude_header(&sb, key, path);
+
+	r = (strcmp(line, sb.buf) ? DESERIALIZE_ERR : DESERIALIZE_OK);
+
+	if (r == DESERIALIZE_ERR)
+		trace_printf_key(&trace_deserialize,
+				 "%s changed [cached '%s'][observed '%s']",
+				 key, line, sb.buf);
+
+	strbuf_release(&sb);
+	return r;
+}
+
+static int my_parse_core_excludes(const char *line)
+{
+	/*
+	 * In dir.c:setup_standard_excludes() they use either the value of
+	 * the "core.excludefile" variable (stored in the global "excludes_file"
+	 * variable) -or- the default value "$XDG_HOME/git/ignore".  This is done
+	 * during wt_status_collect_untracked() which we are hoping to not call.
+	 *
+	 * Fake the setup here.
+	 */
+
+	if (excludes_file) {
+		return my_validate_excludes(excludes_file, "core_excludes", line);
+	} else {
+		char *path = xdg_config_home("ignore");
+		int r = my_validate_excludes(path, "core_excludes", line);
+		free(path);
+		return r;
+	}
+}
+
+static int my_parse_repo_excludes(const char *line)
+{
+	char *path = git_pathdup("info/exclude");
+	int r = my_validate_excludes(path, "repo_excludes", line);
+	free(path);
+
+	return r;
+}
+
+static int wt_deserialize_v1_header(struct wt_status *s, int fd)
+{
+	struct cache_time index_mtime;
+	int line_len, nr_fields;
+	const char *line;
+	const char *arg;
+	int have_required_index_mtime = 0;
+	int have_required_core_excludes = 0;
+	int have_required_repo_excludes = 0;
+
+	/*
+	 * parse header lines up to the first flush packet.
+	 */
+	while ((line = my_packet_read_line(fd, &line_len))) {
+
+		if (skip_prefix(line, "index_mtime ", &arg)) {
+			nr_fields = sscanf(arg, "%d %d",
+					   &index_mtime.sec,
+					   &index_mtime.nsec);
+			if (nr_fields != 2) {
+				trace_printf_key(&trace_deserialize, "invalid index_mtime (%d) '%s'",
+					     nr_fields, line);
+				return DESERIALIZE_ERR;
+			}
+			have_required_index_mtime = 1;
+			continue;
+		}
+
+		if (skip_prefix(line, "core_excludes ", &arg)) {
+			if (my_parse_core_excludes(line) != DESERIALIZE_OK)
+				return DESERIALIZE_ERR;
+			have_required_core_excludes = 1;
+			continue;
+		}
+		if (skip_prefix(line, "repo_excludes ", &arg)) {
+			if (my_parse_repo_excludes(line) != DESERIALIZE_OK)
+				return DESERIALIZE_ERR;
+			have_required_repo_excludes = 1;
+			continue;
+		}
+
+		if (skip_prefix(line, "is_initial ", &arg)) {
+			s->is_initial = (int)strtol(arg, NULL, 10);
+			continue;
+		}
+		if (skip_prefix(line, "branch ", &arg)) {
+			s->branch = xstrdup(arg);
+			continue;
+		}
+		if (skip_prefix(line, "reference ", &arg)) {
+			s->reference = xstrdup(arg);
+			continue;
+		}
+		/* pathspec */
+		/* verbose */
+		/* amend */
+		if (skip_prefix(line, "whence ", &arg)) {
+			s->whence = (int)strtol(arg, NULL, 10);
+			continue;
+		}
+		/* nowarn */
+		/* use_color */
+		/* no_gettext */
+		/* display_comment_prefix */
+		/* relative_paths */
+		/* submodule_summary */
+		if (skip_prefix(line, "show_ignored_mode ", &arg)) {
+			s->show_ignored_mode = (int)strtol(arg, NULL, 10);
+			continue;
+		}
+		if (skip_prefix(line, "show_untracked_files ", &arg)) {
+			s->show_untracked_files = (int)strtol(arg, NULL, 10);
+			continue;
+		}
+		if (skip_prefix(line, "ignore_submodule_arg ", &arg)) {
+			s->ignore_submodule_arg = xstrdup(arg);
+			continue;
+		}
+		/* color_palette */
+		/* colopts */
+		/* null_termination */
+		/* commit_template */
+		/* show_branch */
+		/* show_stash */
+		if (skip_prefix(line, "hints ", &arg)) {
+			s->hints = (int)strtol(arg, NULL, 10);
+			continue;
+		}
+		if (skip_prefix(line, "detect_rename ", &arg)) {
+			s->detect_rename = (int)strtol(arg, NULL, 10);
+			continue;
+		}
+		if (skip_prefix(line, "rename_score ", &arg)) {
+			s->rename_score = (int)strtol(arg, NULL, 10);
+			continue;
+		}
+		if (skip_prefix(line, "rename_limit ", &arg)) {
+			s->rename_limit = (int)strtol(arg, NULL, 10);
+			continue;
+		}
+		/* status_format */
+		if (skip_prefix(line, "sha1_commit ", &arg)) {
+			if (get_sha1_hex(arg, s->sha1_commit)) {
+				trace_printf_key(&trace_deserialize, "invalid sha1_commit");
+				return DESERIALIZE_ERR;
+			}
+			continue;
+		}
+		if (skip_prefix(line, "committable ", &arg)) {
+			s->committable = (int)strtol(arg, NULL, 10);
+			continue;
+		}
+		if (skip_prefix(line, "workdir_dirty ", &arg)) {
+			s->workdir_dirty = (int)strtol(arg, NULL, 10);
+			continue;
+		}
+		/* prefix */
+
+		trace_printf_key(&trace_deserialize, "unexpected line '%s'", line);
+		return DESERIALIZE_ERR;
+	}
+
+	if (!have_required_index_mtime) {
+		trace_printf_key(&trace_deserialize, "missing '%s'", "index_mtime");
+		return DESERIALIZE_ERR;
+	}
+	if (!have_required_core_excludes) {
+		trace_printf_key(&trace_deserialize, "missing '%s'", "core_excludes");
+		return DESERIALIZE_ERR;
+	}
+	if (!have_required_repo_excludes) {
+		trace_printf_key(&trace_deserialize, "missing '%s'", "repo_excludes");
+		return DESERIALIZE_ERR;
+	}
+
+	return my_validate_index(&index_mtime);
+}
+
+/*
+ * Build a string-list of (count) <changed-item> lines from the input.
+ */
+static int wt_deserialize_v1_changed_items(const struct wt_status *cmd_s,
+					   struct wt_status *s, int fd, int count)
+{
+	struct wt_status_serialize_data *sd;
+	char *p;
+	int line_len;
+	const char *line;
+	struct string_list_item *item;
+
+	string_list_init(&s->change, 1);
+
+	/*
+	 * <wt_status_change_data_fields>+
+	 * <flush>
+	 *
+	 * <fixed_part><path> NUL [<head_path>] NUL
+	 */
+	while ((line = my_packet_read_line(fd, &line_len))) {
+		struct wt_status_change_data *d = xcalloc(1, sizeof(*d));
+		sd = (struct wt_status_serialize_data *)line;
+
+		d->worktree_status = ntohl(sd->fixed.worktree_status);
+		d->index_status = ntohl(sd->fixed.index_status);
+		d->stagemask = ntohl(sd->fixed.stagemask);
+		d->rename_status = ntohl(sd->fixed.rename_status);
+		d->rename_score = ntohl(sd->fixed.rename_score);
+		d->mode_head = ntohl(sd->fixed.mode_head);
+		d->mode_index = ntohl(sd->fixed.mode_index);
+		d->mode_worktree = ntohl(sd->fixed.mode_worktree);
+		d->dirty_submodule = ntohl(sd->fixed.dirty_submodule);
+		d->new_submodule_commits = ntohl(sd->fixed.new_submodule_commits);
+		oidcpy(&d->oid_head, &sd->fixed.oid_head);
+		oidcpy(&d->oid_index, &sd->fixed.oid_index);
+
+		p = sd->variant;
+		item = string_list_append(&s->change, p);
+		p += strlen(p) + 1;
+		if (*p)
+			d->rename_source = xstrdup(p);
+		item->util = d;
+		
+		trace_printf_key(
+			&trace_deserialize,
+			"change: %d %d %d %d %d %o %o %o %d %d %s %s '%s' '%s'",
+			d->worktree_status,
+			d->index_status,
+			d->stagemask,
+			d->rename_status,
+			d->rename_score,
+			d->mode_head,
+			d->mode_index,
+			d->mode_worktree,
+			d->dirty_submodule,
+			d->new_submodule_commits,
+			oid_to_hex(&d->oid_head),
+			oid_to_hex(&d->oid_index),
+			item->string,
+			(d->rename_source ? d->rename_source : ""));
+
+		if (d->stagemask &&
+		    cmd_s->status_format == STATUS_FORMAT_PORCELAIN_V2) {
+			/*
+			 * We have an unresolved conflict and the user wants
+			 * to see porcelain V2 output.  The cached status data
+			 * does not contain enough information for V2 (because
+			 * the main status computation does not capture it).
+			 * We only get a single change record for the file with
+			 * a single SHA -- we don't get the stage [123] mode
+			 * and SHA data.  The V2 detail-line print code looks
+			 * up this information directly from the index.  The
+			 * whole point of this serialization cache is to avoid
+			 * reading the index, so the V2 print code gets zeros.
+			 * So we reject the status cache and let the fallback
+			 * code run.
+			 */
+			trace_printf_key(
+				&trace_deserialize,
+				"reject: V2 format and umerged file: %s",
+				item->string);
+			return DESERIALIZE_ERR;
+		}
+	}
+
+	return DESERIALIZE_OK;
+}
+
+static int wt_deserialize_v1_untracked_items(struct wt_status *s,
+					     int fd,
+					     int count,
+					     enum deserialize_parse_strategy strategy)
+{
+	int line_len;
+	const char *line;
+	char *out = NULL;
+	int out_len = 0;
+
+	string_list_init(&s->untracked, 1);
+
+	/*
+	 * <pathname>+
+	 * <flush>
+	 */
+	while ((line = my_packet_read_line(fd, &line_len))) {
+		if (strategy == DESERIALIZE_STRATEGY_AS_IS)
+			string_list_append(&s->untracked, line);
+		if (strategy == DESERIALIZE_STRATEGY_SKIP)
+			continue;
+		if (strategy == DESERIALIZE_STRATEGY_NORMAL) {
+
+			/* Only add "normal" entries to list */
+			if (out &&
+				check_path_contains(out, out_len, line, line_len)) {
+				continue;
+			}
+			else {
+				out = string_list_append(&s->untracked, line)->string;
+				out_len = line_len;
+			}
+		}
+		if (strategy == DESERIALIZE_STRATEGY_ALL) {
+			/* Only add "all" entries to list */
+			if (line[line_len - 1] != '/')
+				string_list_append(&s->untracked, line);
+		}
+	}
+
+	return DESERIALIZE_OK;
+}
+
+static int wt_deserialize_v1_ignored_items(struct wt_status *s,
+					   int fd,
+					   int count,
+					   enum deserialize_parse_strategy strategy)
+{
+	int line_len;
+	const char *line;
+
+	string_list_init(&s->ignored, 1);
+
+	/*
+	 * <pathname>+
+	 * <flush>
+	 */
+	while ((line = my_packet_read_line(fd, &line_len))) {
+		if (strategy == DESERIALIZE_STRATEGY_AS_IS)
+			string_list_append(&s->ignored, line);
+		else
+			continue;
+	}
+
+	return DESERIALIZE_OK;
+}
+
+static int validate_untracked_files_arg(enum untracked_status_type cmd,
+					enum untracked_status_type des,
+					enum deserialize_parse_strategy *strategy)
+{
+	*strategy = DESERIALIZE_STRATEGY_AS_IS;
+
+	if (cmd == des) {
+		*strategy = DESERIALIZE_STRATEGY_AS_IS;
+	} else if (cmd == SHOW_NO_UNTRACKED_FILES) {
+		*strategy = DESERIALIZE_STRATEGY_SKIP;
+	} else if (des == SHOW_COMPLETE_UNTRACKED_FILES) {
+		if (cmd == SHOW_ALL_UNTRACKED_FILES)
+			*strategy = DESERIALIZE_STRATEGY_ALL;
+		else if (cmd == SHOW_NORMAL_UNTRACKED_FILES)
+			*strategy = DESERIALIZE_STRATEGY_NORMAL;
+	} else {
+		return DESERIALIZE_ERR;
+	}
+
+	return DESERIALIZE_OK;
+}
+
+static int validate_ignored_files_arg(enum show_ignored_type cmd,
+				      enum show_ignored_type des,
+				      enum deserialize_parse_strategy *strategy)
+{
+	*strategy = DESERIALIZE_STRATEGY_AS_IS;
+
+	if (cmd == SHOW_NO_IGNORED) {
+		*strategy = DESERIALIZE_STRATEGY_SKIP;
+	}
+	else if (cmd != des) {
+		return DESERIALIZE_ERR;
+	}
+
+	return DESERIALIZE_OK;
+}
+
+static int wt_deserialize_v1(const struct wt_status *cmd_s, struct wt_status *s, int fd)
+{
+	int line_len;
+	const char *line;
+	const char *arg;
+	int nr_changed = 0;
+	int nr_untracked = 0;
+	int nr_ignored = 0;
+
+	enum deserialize_parse_strategy ignored_strategy = DESERIALIZE_STRATEGY_AS_IS, untracked_strategy = DESERIALIZE_STRATEGY_AS_IS;
+
+	if (wt_deserialize_v1_header(s, fd) == DESERIALIZE_ERR)
+		return DESERIALIZE_ERR;
+
+	/*
+	 * We now have the header parsed. Look at the command args (as passed in), and see how to parse
+	 * the serialized data
+	*/
+	if (validate_untracked_files_arg(cmd_s->show_untracked_files, s->show_untracked_files, &untracked_strategy)) {
+		trace_printf_key(&trace_deserialize, "reject: show_untracked_file: command: %d, serialized : %d",
+				cmd_s->show_untracked_files,
+				s->show_untracked_files);
+		return DESERIALIZE_ERR;
+	}
+
+	if (validate_ignored_files_arg(cmd_s->show_ignored_mode, s->show_ignored_mode, &ignored_strategy)) {
+		trace_printf_key(&trace_deserialize, "reject: show_ignored_mode: command: %d, serialized: %d",
+				cmd_s->show_ignored_mode,
+				s->show_ignored_mode);
+		return DESERIALIZE_ERR;
+	}
+
+	/*
+	 * [<changed-header> [<changed-item>+] <flush>]
+	 * [<untracked-header> [<untracked-item>+] <flush>]
+	 * [<ignored-header> [<ignored-item>+] <flush>]
+	 */
+	while ((line = my_packet_read_line(fd, &line_len))) {
+		if (skip_prefix(line, "changed ", &arg)) {
+			nr_changed = (int)strtol(arg, NULL, 10);
+			if (wt_deserialize_v1_changed_items(cmd_s, s, fd, nr_changed)
+			    == DESERIALIZE_ERR)
+				return DESERIALIZE_ERR;
+			continue;
+		}
+		if (skip_prefix(line, "untracked ", &arg)) {
+			nr_untracked = (int)strtol(arg, NULL, 10);
+			if (wt_deserialize_v1_untracked_items(s, fd, nr_untracked, untracked_strategy)
+			    == DESERIALIZE_ERR)
+				return DESERIALIZE_ERR;
+			continue;
+		}
+		if (skip_prefix(line, "ignored ", &arg)) {
+			nr_ignored = (int)strtol(arg, NULL, 10);
+			if (wt_deserialize_v1_ignored_items(s, fd, nr_ignored, ignored_strategy)
+			    == DESERIALIZE_ERR)
+				return DESERIALIZE_ERR;
+			continue;
+		}
+		trace_printf_key(&trace_deserialize, "unexpected line '%s'", line);
+		return DESERIALIZE_ERR;
+	}
+
+	return DESERIALIZE_OK;
+}
+
+static int wt_deserialize_parse(const struct wt_status *cmd_s, struct wt_status *s, int fd)
+{
+	int line_len;
+	const char *line;
+	const char *arg;
+
+	memset(s, 0, sizeof(*s));
+
+	if ((line = my_packet_read_line(fd, &line_len)) &&
+	    (skip_prefix(line, "version ", &arg))) {
+		int version = (int)strtol(arg, NULL, 10);
+		if (version == 1)
+			return wt_deserialize_v1(cmd_s, s, fd);
+	}
+	trace_printf_key(&trace_deserialize, "missing/unsupported version");
+	return DESERIALIZE_ERR;
+}
+
+static inline int my_strcmp_null(const char *a, const char *b)
+{
+	const char *alt_a = (a) ? a : "";
+	const char *alt_b = (b) ? b : "";
+
+	return strcmp(alt_a, alt_b);
+}
+
+static int wt_deserialize_fd(const struct wt_status *cmd_s, struct wt_status *des_s, int fd)
+{
+	memset(des_s, 0, sizeof(*des_s));
+
+	/*
+	 * Check the path spec on the current command
+	 */
+	if (cmd_s->pathspec.nr > 1) {
+		trace_printf_key(&trace_deserialize, "reject: multiple pathspecs");
+		return DESERIALIZE_ERR;
+	}
+
+	/*
+	 * If we have a pathspec, but it maches the root (e.g. no filtering)
+	 * then this is OK.
+	 */
+	if (cmd_s->pathspec.nr == 1 &&
+		my_strcmp_null(cmd_s->pathspec.items[0].match, "")) {
+		trace_printf_key(&trace_deserialize, "reject: pathspec");
+		return DESERIALIZE_ERR;
+	}
+
+	/*
+	 * Deserialize cached status
+	 */
+	if (wt_deserialize_parse(cmd_s, des_s, fd) == DESERIALIZE_ERR)
+		return DESERIALIZE_ERR;
+
+	/*
+	 * Compare fields in cmd_s with those observed in des_s and
+	 * complain if they are incompatible (such as different "-u"
+	 * or "--ignored" settings).
+	 */
+	if (cmd_s->is_initial != des_s->is_initial) {
+		trace_printf_key(&trace_deserialize, "reject: is_initial");
+		return DESERIALIZE_ERR;
+	}
+	if (my_strcmp_null(cmd_s->branch, des_s->branch)) {
+		trace_printf_key(&trace_deserialize, "reject: branch");
+		return DESERIALIZE_ERR;
+	}
+	if (my_strcmp_null(cmd_s->reference, des_s->reference)) {
+		trace_printf_key(&trace_deserialize, "reject: reference");
+		return DESERIALIZE_ERR;
+	}
+	/* verbose */
+	/* amend */
+	if (cmd_s->whence != des_s->whence) {
+		trace_printf_key(&trace_deserialize, "reject: whence");
+		return DESERIALIZE_ERR;
+	}
+	/* nowarn */
+	/* use_color */
+	/* no_gettext */
+	/* display_comment_prefix */
+	/* relative_paths */
+	/* submodule_summary */
+
+	/* show_ignored_files - already validated */
+	/* show_untrackes_files - already validated */
+
+	/*
+	 * Submodules are not supported by status serialization.
+	 * The status will not be serialized if it contains submodules,
+	 * and so this check is not needed.
+	 *
+	 * if (my_strcmp_null(cmd_s->ignore_submodule_arg, des_s->ignore_submodule_arg)) {
+	 *	trace_printf_key(&trace_deserialize, "reject: ignore_submodule_arg");
+	 * 	return DESERIALIZE_ERR;
+	 * }
+	 */
+
+	/* color_palette */
+	/* colopts */
+	/* null_termination */
+	/* commit_template */
+	/* show_branch */
+	/* show_stash */
+	/* hints */
+	/* ahead_behind_flags */
+	if (cmd_s->detect_rename != des_s->detect_rename) {
+		trace_printf_key(&trace_deserialize, "reject: detect_rename");
+		return DESERIALIZE_ERR;
+	}
+	if (cmd_s->rename_score != des_s->rename_score) {
+		trace_printf_key(&trace_deserialize, "reject: rename_score");
+		return DESERIALIZE_ERR;
+	}
+	if (cmd_s->rename_limit != des_s->rename_limit) {
+		trace_printf_key(&trace_deserialize, "reject: rename_limit");
+		return DESERIALIZE_ERR;
+	}
+	/* status_format */
+	if (hashcmp(cmd_s->sha1_commit, des_s->sha1_commit)) {
+		trace_printf_key(&trace_deserialize, "reject: sha1_commit");
+		return DESERIALIZE_ERR;
+	}
+
+	/*
+	 * Copy over display-related fields from the current command.
+	 */
+	des_s->verbose = cmd_s->verbose;
+	/* amend */
+	/* whence */
+	des_s->nowarn = cmd_s->nowarn;
+	des_s->use_color = cmd_s->use_color;
+	des_s->no_gettext = cmd_s->no_gettext;
+	des_s->display_comment_prefix = cmd_s->display_comment_prefix;
+	des_s->relative_paths = cmd_s->relative_paths;
+	des_s->submodule_summary = cmd_s->submodule_summary;
+	memcpy(des_s->color_palette, cmd_s->color_palette,
+	       sizeof(char)*WT_STATUS_MAXSLOT*COLOR_MAXLEN);
+	des_s->colopts = cmd_s->colopts;
+	des_s->null_termination = cmd_s->null_termination;
+	/* commit_template */
+	des_s->show_branch = cmd_s->show_branch;
+	des_s->show_stash = cmd_s->show_stash;
+	/* hints */
+	des_s->ahead_behind_flags = cmd_s->ahead_behind_flags;
+	des_s->status_format = cmd_s->status_format;
+	des_s->fp = cmd_s->fp;
+	if (cmd_s->prefix && *cmd_s->prefix)
+		des_s->prefix = xstrdup(cmd_s->prefix);
+
+	return DESERIALIZE_OK;
+}
+
+static struct cache_time deserialize_prev_mtime = { 0, 0 };
+
+static int try_deserialize_read_from_file_1(const struct wt_status *cmd_s,
+					    const char *path,
+					    struct wt_status *des_s)
+{
+	struct stat st;
+	int result;
+	int fd;
+
+	/*
+	 * If we are spinning waiting for the status cache to become
+	 * valid, skip re-reading it if the mtime has not changed
+	 * since the last time we read it.
+	 */
+	if (lstat(path, &st)) {
+		trace_printf_key(&trace_deserialize,
+				 "could not lstat '%s'", path);
+		return DESERIALIZE_ERR;
+	}
+	if (st.st_mtime == deserialize_prev_mtime.sec &&
+	    ST_MTIME_NSEC(st) == deserialize_prev_mtime.nsec) {
+		trace_printf_key(&trace_deserialize,
+				 "mtime has not changed '%s'", path);
+		return DESERIALIZE_ERR;
+	}
+
+	fd = xopen(path, O_RDONLY);
+	if (fd == -1) {
+		trace_printf_key(&trace_deserialize,
+				 "could not read '%s'", path);
+		return DESERIALIZE_ERR;
+	}
+
+	deserialize_prev_mtime.sec = st.st_mtime;
+	deserialize_prev_mtime.nsec = ST_MTIME_NSEC(st);
+
+	trace_printf_key(&trace_deserialize,
+			 "reading serialization file (%d %d) '%s'",
+			 deserialize_prev_mtime.sec,
+			 deserialize_prev_mtime.nsec,
+			 path);
+
+	result = wt_deserialize_fd(cmd_s, des_s, fd);
+	close(fd);
+
+	return result;
+}
+
+static int try_deserialize_read_from_file(const struct wt_status *cmd_s,
+					  const char *path,
+					  enum wt_status_deserialize_wait dw,
+					  struct wt_status *des_s)
+{
+	int k = 0;
+	int limit;
+	int result = DESERIALIZE_ERR;
+
+	/*
+	 * For "fail" or "no", try exactly once to read the status cache.
+	 * Return an error if the file is stale.
+	 */
+	if (dw == DESERIALIZE_WAIT__FAIL || dw == DESERIALIZE_WAIT__NO) {
+		result = try_deserialize_read_from_file_1(cmd_s, path, des_s);
+		goto done;
+	}
+
+	/*
+	 * Wait for the status cache file to refresh.  Wait duration can
+	 * be in tenths of a second or unlimited.  Poll every 100ms.
+	 */
+	if (dw == DESERIALIZE_WAIT__BLOCK) {
+		/*
+		 * Convert "unlimited" to 1 day.
+		 */
+		limit = 10 * 60 * 60 * 24;
+	} else {
+		/* spin for dw tenths of a second */
+		limit = dw;
+	}
+	for (k = 0; k < limit; k++) {
+		result = try_deserialize_read_from_file_1(
+			cmd_s, path, des_s);
+
+		if (result == DESERIALIZE_OK)
+			break;
+
+		sleep_millisec(100);
+	}
+
+done:
+	trace2_data_string("status", the_repository, "deserialize/path", path);
+	trace2_data_intmax("status", the_repository, "deserialize/polled", k);
+	trace2_data_string("status", the_repository, "deserialize/result",
+			   ((result == DESERIALIZE_OK) ? "ok" : "reject"));
+
+	trace_printf_key(&trace_deserialize,
+			 "wait polled=%d result=%d '%s'",
+			 k, result, path);
+	return result;
+}
+
+/*
+ * Read raw serialized status data from the given file (or STDIN).
+ *
+ * Verify that the args specified in the current command
+ * are compatible with the deserialized data (such as "-uno").
+ *
+ * Copy display-related fields from the current command
+ * into the deserialized data (so that the user can request
+ * long or short as they please).
+ *
+ * Print status report using cached data.
+ */
+int wt_status_deserialize(const struct wt_status *cmd_s,
+			  const char *path,
+			  enum wt_status_deserialize_wait dw)
+{
+	struct wt_status des_s;
+	int result;
+
+	trace2_region_enter("status", "deserialize", the_repository);
+
+	if (path && *path && strcmp(path, "0")) {
+		result = try_deserialize_read_from_file(cmd_s, path, dw, &des_s);
+	} else {
+		trace_printf_key(&trace_deserialize, "reading stdin");
+
+		/*
+		 * Read status cache data from stdin.  Ignore the deserialize-wait
+		 * term, since we cannot read stdin multiple times.
+		 */
+		result = wt_deserialize_fd(cmd_s, &des_s, 0);
+
+		trace2_data_string("status", the_repository, "deserialize/path", "STDIN");
+		trace2_data_string("status", the_repository, "deserialize/result",
+				   ((result == DESERIALIZE_OK) ? "ok" : "reject"));
+	}
+
+	trace2_region_leave("status", "deserialize", the_repository);
+
+	if (result == DESERIALIZE_OK) {
+		wt_status_get_state(&des_s.state, des_s.branch &&
+				    !strcmp(des_s.branch, "HEAD"));
+		wt_status_print(&des_s);
+	}
+
+	return result;
+}
diff --git a/wt-status-serialize.c b/wt-status-serialize.c
new file mode 100644
index 00000000000000..ff0a718e7d51ad
--- /dev/null
+++ b/wt-status-serialize.c
@@ -0,0 +1,333 @@
+#include "cache.h"
+#include "wt-status.h"
+#include "pkt-line.h"
+
+static struct trace_key trace_serialize = TRACE_KEY_INIT(SERIALIZE);
+
+/*
+ * Compute header record for exclude file using format:
+ *      <key> SP <status_char> SP <variant> LF
+ */
+void wt_serialize_compute_exclude_header(struct strbuf *sb,
+					 const char *key,
+					 const char *path)
+{
+	struct stat st;
+	struct stat_data sd;
+
+	memset(&sd, 0, sizeof(sd));
+
+	strbuf_setlen(sb, 0);
+
+	if (!path || !*path) {
+		strbuf_addf(sb, "%s U (unset)", key);
+	} else if (lstat(path, &st) == -1) {
+		if (is_missing_file_error(errno))
+			strbuf_addf(sb, "%s E (not-found) %s", key, path);
+		else
+			strbuf_addf(sb, "%s E (other) %s", key, path);
+	} else {
+		fill_stat_data(&sd, &st);
+		strbuf_addf(sb, "%s F %d %d %s",
+			    key, sd.sd_mtime.sec, sd.sd_mtime.nsec, path);
+	}
+}
+
+static void append_exclude_info(int fd, const char *path, const char *key)
+{
+	struct strbuf sb = STRBUF_INIT;
+
+	wt_serialize_compute_exclude_header(&sb, key, path);
+
+	packet_write_fmt(fd, "%s\n", sb.buf);
+
+	strbuf_release(&sb);
+}
+
+static void append_core_excludes_file_info(int fd)
+{
+	/*
+	 * Write pathname and mtime of the core/global excludes file to
+	 * the status cache header.  Since a change in the global excludes
+	 * will/may change the results reported by status, the deserialize
+	 * code should be able to reject the status cache if the excludes
+	 * file changes since when the cache was written.
+	 *
+	 * The "core.excludefile" setting defaults to $XDG_HOME/git/ignore
+	 * and uses a global variable which should have been set during
+	 * wt_status_collect_untracked().
+	 *
+	 * See dir.c:setup_standard_excludes()
+	 */
+	append_exclude_info(fd, excludes_file, "core_excludes");
+}
+
+static void append_repo_excludes_file_info(int fd)
+{
+	/*
+	 * Likewise, there is a per-repo excludes file in .git/info/excludes
+	 * that can change the results reported by status.  And the deserialize
+	 * code needs to be able to reject the status cache if this file
+	 * changes.
+	 *
+	 * See dir.c:setup_standard_excludes() and git_path_info_excludes().
+	 * We replicate the pathname construction here because of the static
+	 * variables/functions used in dir.c.
+	 */
+	char *path = git_pathdup("info/exclude");
+
+	append_exclude_info(fd, path, "repo_excludes");
+
+	free(path);
+}
+
+/*
+ * WARNING: The status cache attempts to preserve the essential in-memory
+ * status data after a status scan into a "serialization" (aka "status cache")
+ * file.  It allows later "git status --deserialize=<foo>" instances to
+ * just print the cached status results without scanning the workdir (and
+ * without reading the index).
+ *
+ * The status cache file is valid as long as:
+ * [1] the set of functional command line options are the same (think "-u").
+ * [2] repo-local and user-global configuration settings are compatible.
+ * [3] nothing in the workdir has changed.
+ *
+ * We rely on:
+ * [1.a] We remember the relevant (functional, non-display) command line
+ *       arguments in the status cache header.
+ * [2.a] We use the mtime of the .git/index to detect staging changes.
+ * [2.b] We use the mtimes of the excludes files to detect changes that
+ *      might affect untracked file reporting.
+ *
+ * But we need external help to verify [3].
+ * [] This includes changes to tracked files.
+ * [] This includes changes to tracked .gitignore files that might change
+ *    untracked file reporting.
+ * [] This includes the creation of new, untracked per-directory .gitignore
+ *    files that might change untracked file reporting.
+ *
+ * [3.a] On GVFS repos, we rely on the GVFS service (mount) daemon to
+ *      watch the filesystem and invalidate (delete) the status cache
+ *      when anything changes inside the workdir.
+ *
+ * [3.b] TODO This problem is not solved for non-GVFS repos.
+ *       [] It is possible that the untracked-cache index extension
+ *          could help with this but that requires status to read the
+ *          index to load the extension.
+ *       [] It is possible that the new fsmonitor facility could also
+ *          provide this information, but that to requires reading the
+ *          index.
+ */
+
+/*
+ * Write V1 header fields.
+ */
+static void wt_serialize_v1_header(struct wt_status *s, int fd)
+{
+	/*
+	 * Write select fields from the current index to help
+	 * the deserializer recognize a stale data set.
+	 */
+	packet_write_fmt(fd, "index_mtime %d %d\n",
+			 the_index.timestamp.sec,
+			 the_index.timestamp.nsec);
+	append_core_excludes_file_info(fd);
+	append_repo_excludes_file_info(fd);
+
+	/*
+	 * Write data from wt_status to qualify this status report.
+	 * That is, if this run specified "-uno", the consumer of
+	 * our serialization should know that.
+	 */
+	packet_write_fmt(fd, "is_initial %d\n", s->is_initial);
+	if (s->branch)
+		packet_write_fmt(fd, "branch %s\n", s->branch);
+	if (s->reference)
+		packet_write_fmt(fd, "reference %s\n", s->reference);
+	/* pathspec */
+	/* verbose */
+	/* amend */
+	packet_write_fmt(fd, "whence %d\n", s->whence);
+	/* nowarn */
+	/* use_color */
+	/* no_gettext */
+	/* display_comment_prefix */
+	/* relative_paths */
+	/* submodule_summary */
+	packet_write_fmt(fd, "show_ignored_mode %d\n", s->show_ignored_mode);
+	packet_write_fmt(fd, "show_untracked_files %d\n", s->show_untracked_files);
+	if (s->ignore_submodule_arg)
+		packet_write_fmt(fd, "ignore_submodule_arg %s\n", s->ignore_submodule_arg);
+	/* color_palette */
+	/* colopts */
+	/* null_termination */
+	/* commit_template */
+	/* show_branch */
+	/* show_stash */
+	packet_write_fmt(fd, "hints %d\n", s->hints);
+	/* ahead_behind_flags */
+	packet_write_fmt(fd, "detect_rename %d\n", s->detect_rename);
+	packet_write_fmt(fd, "rename_score %d\n", s->rename_score);
+	packet_write_fmt(fd, "rename_limit %d\n", s->rename_limit);
+	/* status_format */
+	packet_write_fmt(fd, "sha1_commit %s\n", sha1_to_hex(s->sha1_commit));
+	packet_write_fmt(fd, "committable %d\n", s->committable);
+	packet_write_fmt(fd, "workdir_dirty %d\n", s->workdir_dirty);
+	/* prefix */
+	packet_flush(fd);
+}
+
+/*
+ * Print changed/unmerged items.
+ * We write raw (not c-quoted) pathname(s).  The rename_source is only
+ * set when status computed a rename/copy.
+ *
+ * We ALWAYS write a final LF to the packet-line (for debugging)
+ * even though Linux pathnames allow LFs.
+ */
+static inline void wt_serialize_v1_changed(struct wt_status *s, int fd,
+					   struct string_list_item *item)
+{
+	struct wt_status_change_data *d = item->util;
+	struct wt_status_serialize_data sd;
+	char *begin;
+	char *end;
+	char *p;
+	int len_path, len_rename_source;
+
+	trace_printf_key(&trace_serialize,
+		"change: %d %d %d %d %d %o %o %o %d %d %s %s '%s' '%s'",
+		d->worktree_status,
+		d->index_status,
+		d->stagemask,
+		d->rename_status,
+		d->rename_score,
+		d->mode_head,
+		d->mode_index,
+		d->mode_worktree,
+		d->dirty_submodule,
+		d->new_submodule_commits,
+		oid_to_hex(&d->oid_head),
+		oid_to_hex(&d->oid_index),
+		item->string,
+		(d->rename_source ? d->rename_source : ""));
+
+	sd.fixed.worktree_status       = htonl(d->worktree_status);
+	sd.fixed.index_status          = htonl(d->index_status);
+	sd.fixed.stagemask             = htonl(d->stagemask);
+	sd.fixed.rename_status         = htonl(d->rename_status);
+	sd.fixed.rename_score          = htonl(d->rename_score);
+	sd.fixed.mode_head             = htonl(d->mode_head);
+	sd.fixed.mode_index            = htonl(d->mode_index);
+	sd.fixed.mode_worktree         = htonl(d->mode_worktree);
+	sd.fixed.dirty_submodule       = htonl(d->dirty_submodule);
+	sd.fixed.new_submodule_commits = htonl(d->new_submodule_commits);
+	oidcpy(&sd.fixed.oid_head,  &d->oid_head);
+	oidcpy(&sd.fixed.oid_index, &d->oid_index);
+
+	begin = (char *)&sd;
+	end = begin + sizeof(sd);
+
+	p = sd.variant;
+
+	/*
+	 * Write <path> NUL [<rename_source>] NUL LF at the end of the buffer.
+	 */
+	len_path = strlen(item->string);
+	len_rename_source = d->rename_source ? strlen(d->rename_source) : 0;
+
+	/*
+	 * This is a bit of a hack, but I don't want to split the
+	 * status detail record across multiple pkt-lines.
+	 */
+	if (p + len_path + 1 + len_rename_source + 1 + 1 >= end)
+		BUG("path to long to serialize '%s'", item->string);
+
+	memcpy(p, item->string, len_path);
+	p += len_path;
+	*p++ = '\0';
+
+	if (len_rename_source) {
+		memcpy(p, d->rename_source, len_rename_source);
+		p += len_rename_source;
+	}
+	*p++ = '\0';
+	*p++ = '\n';
+
+	if (packet_write_gently(fd, begin, (p - begin)))
+		BUG("cannot serialize '%s'", item->string);
+}
+
+/*
+ * Write raw (not c-quoted) pathname for an untracked item.
+ * We ALWAYS write a final LF to the packet-line (for debugging)
+ * even though Linux pathnames allows LFs.  That is, deserialization
+ * should use the packet-line length and omit the final LF.
+ */
+static inline void wt_serialize_v1_untracked(struct wt_status *s, int fd,
+					     struct string_list_item *item)
+{
+	packet_write_fmt(fd, "%s\n", item->string);
+}
+
+/*
+ * Write raw (not c-quoted) pathname for an ignored item.
+ * We ALWAYS write a final LF to the packet-line (for debugging)
+ * even though Linux pathnames allows LFs.
+ */
+static inline void wt_serialize_v1_ignored(struct wt_status *s, int fd,
+					   struct string_list_item *item)
+{
+	packet_write_fmt(fd, "%s\n", item->string);
+}
+
+/*
+ * Serialize the list of changes to the given file.  The goal of this
+ * is to just serialize the key fields in wt_status so that a
+ * later command can rebuilt it and do the printing.
+ *
+ * We DO NOT include the contents of wt_status_state NOR
+ * current branch info.  This info easily gets stale and
+ * is relatively quick for the status consumer to compute
+ * as necessary.
+ */
+void wt_status_serialize_v1(int fd, struct wt_status *s)
+{
+	struct string_list_item *iter;
+	int k;
+
+	/*
+	 * version header must be first line.
+	 */
+	packet_write_fmt(fd, "version 1\n");
+
+	wt_serialize_v1_header(s, fd);
+
+	if (s->change.nr > 0) {
+		packet_write_fmt(fd, "changed %d\n", s->change.nr);
+		for (k = 0; k < s->change.nr; k++) {
+			iter = &(s->change.items[k]);
+			wt_serialize_v1_changed(s, fd, iter);
+		}
+		packet_flush(fd);
+	}
+
+	if (s->untracked.nr > 0) {
+		packet_write_fmt(fd, "untracked %d\n", s->untracked.nr);
+		for (k = 0; k < s->untracked.nr; k++) {
+			iter = &(s->untracked.items[k]);
+			wt_serialize_v1_untracked(s, fd, iter);
+		}
+		packet_flush(fd);
+	}
+
+	if (s->ignored.nr > 0) {
+		packet_write_fmt(fd, "ignored %d\n", s->ignored.nr);
+		for (k = 0; k < s->ignored.nr; k++) {
+			iter = &(s->ignored.items[k]);
+			wt_serialize_v1_ignored(s, fd, iter);
+		}
+		packet_flush(fd);
+	}
+}
diff --git a/wt-status.c b/wt-status.c
index a24711374c4191..682186ed76b47a 100644
--- a/wt-status.c
+++ b/wt-status.c
@@ -18,6 +18,8 @@
 #include "worktree.h"
 #include "lockfile.h"
 
+#define AB_DELAY_WARNING_IN_MS (2 * 1000)
+
 static const char cut_line[] =
 "------------------------ >8 ------------------------\n";
 
@@ -692,6 +694,9 @@ static void wt_status_collect_untracked(struct wt_status *s)
 	if (s->show_untracked_files != SHOW_ALL_UNTRACKED_FILES)
 		dir.flags |=
 			DIR_SHOW_OTHER_DIRECTORIES | DIR_HIDE_EMPTY_DIRECTORIES;
+	if (s->show_untracked_files == SHOW_COMPLETE_UNTRACKED_FILES)
+		dir.flags |= DIR_KEEP_UNTRACKED_CONTENTS;
+
 	if (s->show_ignored_mode) {
 		dir.flags |= DIR_SHOW_IGNORED_TOO;
 
@@ -744,16 +749,29 @@ static int has_unmerged(struct wt_status *s)
 
 void wt_status_collect(struct wt_status *s)
 {
+	trace2_region_enter("status", "worktrees", the_repository);
 	wt_status_collect_changes_worktree(s);
-	if (s->is_initial)
+	trace2_region_leave("status", "worktrees", the_repository);
+
+	if (s->is_initial) {
+		trace2_region_enter("status", "initial", the_repository);
 		wt_status_collect_changes_initial(s);
-	else
+		trace2_region_leave("status", "initial", the_repository);
+	} else {
+		trace2_region_enter("status", "index", the_repository);
 		wt_status_collect_changes_index(s);
+		trace2_region_leave("status", "index", the_repository);
+	}
+
+	trace2_region_enter("status", "untracked", the_repository);
 	wt_status_collect_untracked(s);
+	trace2_region_leave("status", "untracked", the_repository);
 
+	trace2_region_enter("status", "committable", the_repository);
 	wt_status_get_state(&s->state, s->branch && !strcmp(s->branch, "HEAD"));
 	if (s->state.merge_in_progress && !has_unmerged(s))
 		s->committable = 1;
+	trace2_region_leave("status", "committable", the_repository);
 }
 
 void wt_status_collect_free_buffers(struct wt_status *s)
@@ -1063,14 +1081,29 @@ static void wt_longstatus_print_tracking(struct wt_status *s)
 	struct branch *branch;
 	char comment_line_string[3];
 	int i;
+	uint64_t t_begin = 0;
 
 	assert(s->branch && !s->is_initial);
 	if (!skip_prefix(s->branch, "refs/heads/", &branch_name))
 		return;
 	branch = branch_get(branch_name);
+
+	t_begin = getnanotime();
+
 	if (!format_tracking_info(branch, &sb, s->ahead_behind_flags))
 		return;
 
+	if (advice_status_ahead_behind_warning &&
+	    s->ahead_behind_flags == AHEAD_BEHIND_FULL) {
+		uint64_t t_delta_in_ms = (getnanotime() - t_begin) / 1000000;
+		if (t_delta_in_ms > AB_DELAY_WARNING_IN_MS) {
+			strbuf_addf(&sb, _("\n"
+					   "It took %.2f seconds to compute the branch ahead/behind values.\n"
+					   "You can use '--no-ahead-behind' to avoid this.\n"),
+				    t_delta_in_ms / 1000.0);
+		}
+	}
+
 	i = 0;
 	if (s->display_comment_prefix) {
 		comment_line_string[i++] = comment_line_char;
@@ -2301,6 +2334,9 @@ void wt_status_print(struct wt_status *s)
 	case STATUS_FORMAT_LONG:
 		wt_longstatus_print(s);
 		break;
+	case STATUS_FORMAT_SERIALIZE_V1:
+		wt_status_serialize_v1(1, s);
+		break;
 	}
 }
 
diff --git a/wt-status.h b/wt-status.h
index 1fcf93afbf57a9..ca0ac6fab38c6b 100644
--- a/wt-status.h
+++ b/wt-status.h
@@ -5,6 +5,7 @@
 #include "string-list.h"
 #include "color.h"
 #include "pathspec.h"
+#include "pkt-line.h"
 #include "remote.h"
 
 struct worktree;
@@ -25,7 +26,8 @@ enum color_wt_status {
 enum untracked_status_type {
 	SHOW_NO_UNTRACKED_FILES,
 	SHOW_NORMAL_UNTRACKED_FILES,
-	SHOW_ALL_UNTRACKED_FILES
+	SHOW_ALL_UNTRACKED_FILES,
+	SHOW_COMPLETE_UNTRACKED_FILES,
 };
 
 enum show_ignored_type {
@@ -60,6 +62,7 @@ enum wt_status_format {
 	STATUS_FORMAT_SHORT,
 	STATUS_FORMAT_PORCELAIN,
 	STATUS_FORMAT_PORCELAIN_V2,
+	STATUS_FORMAT_SERIALIZE_V1,
 
 	STATUS_FORMAT_UNSPECIFIED
 };
@@ -149,4 +152,70 @@ int has_uncommitted_changes(int ignore_submodules);
 int require_clean_work_tree(const char *action, const char *hint,
 	int ignore_submodules, int gently);
 
+#define DESERIALIZE_OK  0
+#define DESERIALIZE_ERR 1
+
+struct wt_status_serialize_data_fixed
+{
+	uint32_t worktree_status;
+	uint32_t index_status;
+	uint32_t stagemask;
+	uint32_t rename_status;
+	uint32_t rename_score;
+	uint32_t mode_head;
+	uint32_t mode_index;
+	uint32_t mode_worktree;
+	uint32_t dirty_submodule;
+	uint32_t new_submodule_commits;
+	struct object_id oid_head;
+	struct object_id oid_index;
+};
+
+/*
+ * Consume the maximum amount of data possible in a
+ * packet-line record.  This is overkill because we
+ * have at most 2 relative pathnames, but means we
+ * don't need to allocate a variable length structure.
+ */
+struct wt_status_serialize_data
+{
+	struct wt_status_serialize_data_fixed fixed;
+	char variant[LARGE_PACKET_DATA_MAX
+		     - sizeof(struct wt_status_serialize_data_fixed)];
+};
+
+enum wt_status_deserialize_wait
+{
+	DESERIALIZE_WAIT__UNSET = -3,
+	DESERIALIZE_WAIT__FAIL = -2, /* return error, do not fallback */
+	DESERIALIZE_WAIT__BLOCK = -1, /* unlimited timeout */
+	DESERIALIZE_WAIT__NO = 0, /* immediately fallback */
+	/* any positive value is a timeout in tenths of a second */
+};
+
+/*
+ * Serialize computed status scan results using "version 1" format
+ * to the given file.
+ */
+void wt_status_serialize_v1(int fd, struct wt_status *s);
+
+/*
+ * Deserialize existing status results from the given file and
+ * populate a (new) "struct wt_status".  Use the contents of "cmd_s"
+ * (computed from the command line arguments) to verify that the
+ * cached data is compatible and overlay various display-related
+ * fields.
+ */
+int wt_status_deserialize(const struct wt_status *cmd_s,
+			  const char *path,
+			  enum wt_status_deserialize_wait dw);
+
+/*
+ * A helper routine for serialize and deserialize to compute
+ * metadata for the user-global and repo-local excludes files.
+ */
+void wt_serialize_compute_exclude_header(struct strbuf *sb,
+					 const char *key,
+					 const char *path);
+
 #endif /* STATUS_H */