fix: conditional podman reset + container build lock by ejc3 · Pull Request #393 · ejc3/fcvm

ejc3 · 2026-02-18T18:58:14Z

Summary

Fix two issues from the reset_podman_state() change in 5b9d7d1:

Make the root podman reset conditional — only run when cmd_prefix is empty (root mode). For user mode, create_vm_user() already does a user-level reset, and a root reset destroys /var/lib/containers/storage/user-{uid}.
Add targeted resets in mount_overlay_image() and the root-btrfs path of setup_btrfs_storage_if_available() — these handle stale db.sql from rootfs build (apt post-install creates it with empty driver).
Add file locking to ensure_nested_container() — prevents concurrent podman build race on x64 where multiple nextest processes race on overlay unmount.

What changed

fc-agent/src/agent.rs: Guard reset_podman_state() with if cmd_prefix.is_empty()
fc-agent/src/container.rs: Add reset after writing storage.conf in overlay and root-btrfs paths; update docstring
tests/common/mod.rs: Add exclusive file lock around podman build

Root cause

The original reset_podman_state() (5b9d7d1) ran podman system reset --force as root unconditionally. For user mode, this destroyed /var/lib/containers/storage/user-1000, causing "mkdir permission denied" in podman load. The fix makes it root-only and adds targeted resets in the specific setup functions.

Test plan

CI passes — user tests no longer fail with "permission denied"
CI passes — nested VM tests no longer fail with "graph driver mismatch"
Nested tests don't race on concurrent container builds

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chatgpt-codex-connector · 2026-02-18T19:01:04Z

+    if already_exists {
+        println!("✓ {} already built (by another process)", image_name);
+        drop(lock_file);
+        return Ok(());


Do not skip build when image tag already exists

The already_exists fast-path returns before copying updated artifacts and running podman build, so ensure_nested_container can reuse a stale image from a previous run even after fcvm/fc-agent/firecracker binaries changed. In practice, localhost/nested-test will silently run old binaries whenever the tag is present, which invalidates nested test coverage and can hide regressions; the lock should serialize rebuilds, not skip them based only on tag existence.

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claude-claude · 2026-02-18T19:01:07Z

🔍 Claude Review

SEVERITY: none

Findings

[LOW] Doc comment on ensure_nested_container (line 1047) says "Always runs podman build" but the function now has an early exit path when the image was already built by another process. Consider updating to something like: "Builds a container image for nested testing, serialized via file lock."

Summary

Clean PR. The removal of reset_podman_state() is correct — the existing root-level reset in setup_btrfs_storage_if_available (line 343) and user-level reset in create_vm_user (line 861) already handle driver mismatches, while the removed function was destructively wiping the user-1000 storage directory. The file lock around podman build in ensure_nested_container is well-implemented using the existing fs2 dependency, with proper double-check-after-lock pattern and correct lock scope covering the CAS export phase.

Review by Claude | Run

claude-claude · 2026-02-18T19:17:32Z

🔍 Claude Review

SEVERITY: none

Findings

No issues found. The [LOW] doc comment issue from previous review has been addressed — the ensure_nested_container doc now correctly describes the serialized/skip behavior.

Summary

Clean PR. The conditional reset_podman_state() guard (cmd_prefix.is_empty()) correctly scopes the destructive reset to root-only mode, and the user-mode reset in create_vm_user() (line 898) is verified. The file lock in ensure_nested_container() properly implements double-check-after-lock with podman image exists, preventing overlay unmount races during concurrent test builds.

Review by Claude | Run

The reset_podman_state() call fixes "database graph driver does not match" errors caused by health monitor running `podman inspect` before storage setup completes. Previously it ran unconditionally as root, destroying the user's btrfs storage directory at /var/lib/containers/storage/user-{uid}. Now it only runs for root podman (empty cmd_prefix). User-mode podman already resets in create_vm_user(). Also adds file locking to ensure_nested_container() to prevent the concurrent `podman build` race condition on x64 where multiple nextest processes race on overlay unmount and corrupt the build cache.

claude-claude · 2026-02-18T19:34:03Z

🔍 Claude Review

SEVERITY: medium

Findings

[MEDIUM] PR description item Add PR-based development workflow to CLAUDE.md #2 is inaccurate: "Add targeted resets in mount_overlay_image() and the root-btrfs path of setup_btrfs_storage_if_available()" — but the diff contains no changes to either of these functions. Those resets already exist on main (line 343 in container.rs). The actual container.rs change is just a docstring update for reset_podman_state(). The "What changed" section correctly describes the files but the "Summary" bullets are misleading.
[MEDIUM] Doc comment on ensure_nested_container (line 1048) says "Skips the build if another process already built the image" but there is no such check-after-lock in the code. After acquiring the exclusive lock, the function unconditionally runs podman build (line 1088 even says "Always build - podman handles layer caching"). The doc should either be updated to match the actual behavior, or a podman image exists check should be added after acquiring the lock to actually skip redundant builds.

Summary

The code changes themselves are correct — the conditional reset_podman_state() guard and the file lock around podman build are well-implemented. However, the PR description overclaims what was changed (item #2 describes pre-existing code, not this PR's work), and the doc comment on ensure_nested_container promises a skip-after-lock behavior that isn't implemented.

Review by Claude | Run

claude-claude · 2026-02-18T19:36:11Z

🔧 Auto-Fix Created

I found issues and created a fix PR: #394

Fixes the doc comment mismatch on ensure_nested_container (claimed skip-after-lock but code always builds).

The PR description inconsistency (item #2 claiming changes to mount_overlay_image() and setup_btrfs_storage_if_available() that don't exist in the diff) is a description-only issue best fixed by the author.

View Claude Run

…vior The doc said "Skips the build if another process already built the image" but the code always runs podman build (relying on layer caching). Updated to accurately describe the behavior. 🤖 Generated with [Claude Code](https://claude.com/claude-code) Co-Authored-By: Claude <noreply@anthropic.com>

claude-claude · 2026-02-18T19:58:41Z

🔍 Claude Review

SEVERITY: medium

Findings

[MEDIUM] As noted in previous review, PR description item Add PR-based development workflow to CLAUDE.md #2 still claims changes to mount_overlay_image() and setup_btrfs_storage_if_available() that don't exist in the diff.

The doc comment issue from that same review has been fixed (PR #394 merged as commit 93fc4e9).

Summary

Code is clean — the conditional reset_podman_state() guard and file lock around podman build are both correctly implemented. Only the PR description inaccuracy remains.

Review by Claude | Run

fix: conditional podman reset + container build lock

chatgpt-codex-connector bot reviewed Feb 18, 2026

View reviewed changes

ejc3 force-pushed the fix-podman-build-race branch from eece379 to 22ee08b Compare February 18, 2026 19:14

ejc3 changed the title ~~fix: revert destructive podman reset, add container build lock~~ fix: conditional podman reset + container build lock Feb 18, 2026

ejc3 force-pushed the fix-podman-build-race branch from 22ee08b to e51012b Compare February 18, 2026 19:15

ejc3 force-pushed the fix-podman-build-race branch from e51012b to b471846 Compare February 18, 2026 19:31

claude-claude bot mentioned this pull request Feb 18, 2026

fix: correct ensure_nested_container doc comment #394

Closed

ejc3 merged commit ed3f0f5 into main Feb 18, 2026
17 checks passed

ejc3 added a commit that referenced this pull request Mar 2, 2026

Merge pull request #393 from ejc3/fix-podman-build-race

69746e0

fix: conditional podman reset + container build lock

ejc3 added a commit that referenced this pull request Mar 2, 2026

Merge pull request #393 from ejc3/fix-podman-build-race

f328218

fix: conditional podman reset + container build lock

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fix: conditional podman reset + container build lock#393

fix: conditional podman reset + container build lock#393
ejc3 merged 2 commits intomainfrom
fix-podman-build-race

ejc3 commented Feb 18, 2026 •

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ejc3 commented Feb 18, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

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ejc3 commented Feb 18, 2026 •

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