Files on Unmounted Mounts
summary
CRIU fails to checkpoint files opened on mounts detached with MNT_DETACH because /proc lacks mountinfo for those mounts; two kernel changes are proposed: a special unmount_mnt_ns to house detached mounts (rejected for correctness, locking and visibility issues) and an fd-based statmount by FD that returns mountinfo for the mount behind a given fd. The accepted patch (v7) adds statmount(fd) with no extra capability checks, supports checkpoint/restore of detached bind mounts by creating temporary mountpoints and re-detaching them, and leaves anonymous-mount and dump-of-filesystem cases for future work.
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chapters (9)
- 0:00Introduction to unmounted mounts
- 1:48First approach with unmount namespace
- 3:16Second approach with stat mount by FD
- 5:26Checkpoint restore implementation
- 8:12Q&A on mount restoration
- 13:33Global identifiers and limitations
- 16:40Checkpoint restore challenges
- 17:42Benefits of stat mount on FDs
- 19:05Closing remarks and Q&A end
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