[PATCHBOMB 6.19] xfs: autonomous self healing

["Darrick J. Wong" <djwong@kernel.org>]

Hi everyone,

You might recall that 18 months ago I showed off an early draft of a
patchset implementing autonomous self healing capabilities for XFS.
The premise is quite simple -- add a few hooks to the kernel to capture
significant filesystem metadata and file health events (pretty much all
failures), queue these events to a special anonfd, and let userspace
read the events at its leisure.  That's patchset 1.

The userspace part is more interesting, because there's a new daemon
that opens the anonfd given the root dir of a filesystem, captures a
file handle for the root dir, detaches from the root dir, and waits for
metadata events.  Upon receipt of an adverse health event, it will
reopen the root directory and initiate repairs.  I've left the prototype
Python script in place (patchset 2) but my ultimate goal is for everyone
to use the Rust version (patchset 3) because it's much quicker to
respond to problems.

New QA tests are patchset 4.  Zorro: No need to merge this right away.

This work was mostly complete by the end of 2024, and I've been letting
it run on my XFS QA testing fleets ever since then.  I am submitting
this patchset for upstream for 6.19.  Once this is merged, the online
fsck project will be complete.

--D