borg mount only a selected PATH (as in extract)

[alejandro-perez]

Given the fairly amount of CPU power needed for the "versions" option (which I found utterly useful), I'd like to ask for restrict the mount to just a specific PATH. IMO, the use of the versions option typically means you are looking for the versions of a (some) specific (set of) file(s).

E.g. OMG! Someone, at some time, modified "Documents/Important/analysis.odt". I need to recover the previous version (whenever it was). I don't want to mount all the (potentially huge) directory tree with all the versions. Just that file/directory.

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💰 there is a bounty for this

[ThomasWaldmann]

@alejandro-perez sounds useful.

Not sure if it would help much with the processing time needed because to find all files below some specific path, borg still has to read through the whole archives. But at least it would save some memory, as all non-matching fs objects would not have to get created in memory.

Another idea (not sure if already implemented or still todo) is to only process a subset of all archives (like last 10, all with some specific prefix, ...) and not all of them.

[alejandro-perez]

It is always faster to do not create objects, etc (maybe not breathtaking improvement, but I guess it should be at least noticeable).
Regarding the subset of archives, I've seen that beta version does allow to select a specific prefix with -P (1.0.9 does not).

[alejandro-perez]

Note when I mentioned performance imporvements I meant with the "-o versions" option, which is more CPU intensive that just mounting the archives as they are.

[enkore]

If it doesn't already, borg-mount should do the standard set of --last/--first/--prefix options that a bunch of other commands also have implemented in common.

[ThomasWaldmann]

since borg 1.1, borg mount already supports --first, --last, --prefix and --glob-archives to only work on a subset of all archives.

[ThomasWaldmann]

Notes:

• hardlink_masters potentially not being present in the selected items complicates things, as usual. code for this exists for e.g. do_extract.
• to check: does borg mount currently hide part files? filtering them also exists as part of do_extract match/filter mechanism.

[alejandro-perez]

since borg 1.1, borg mount already supports --first, --last, --prefix and --glob-archives to only work on a subset of all archives.

This allows you to select a number of archives, but I was thinking of a set of files rather than archives.
Use case: I want to see all the versions of just one file in home/alex/a_file_that_changes_a_lot.odt, I'd rather not process the whole repository.

[ThomasWaldmann]

@alejandro-perez yes, we understood that. but as we were also talking about the archive options, I wanted to clarify that. i am currently working on adding what you'ld like to have in #3300.

[alejandro-perez]

@ThomasWaldmann Thanks!