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04a65666a6
xfs: autonomous self healing of filesystems [v7] This patchset builds new functionality to deliver live information about filesystem health events to userspace. This is done by creating an anonymous file that can be read() for events by userspace programs. Events are captured by hooking various parts of XFS and iomap so that metadata health failures, file I/O errors, and major changes in filesystem state (unmounts, shutdowns, etc.) can be observed by programs. When an event occurs, the hook functions queue an event object to each event anonfd for later processing. Programs must have CAP_SYS_ADMIN to open the anonfd and there's a maximum event lag to prevent resource overconsumption. The events themselves can be read() from the anonfd as C structs for the xfs_healer daemon. In userspace, we create a new daemon program that will read the event objects and initiate repairs automatically. This daemon is managed entirely by systemd and will not block unmounting of the filesystem unless repairs are ongoing. They are auto-started by a starter service that uses fanotify. This patchset depends on the new fserror code that Christian Brauner has tentatively accepted for Linux 7.0: https://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs.git/log/?h=vfs-7.0.fserror v7: more cleanups of the media verification ioctl, improve comments, and reuse the bio v6: fix pi-breaking bugs, make verify failures trigger health reports and filter bio status flags better v5: add verify-media ioctl, collapse small helper funcs with only one caller v4: drop multiple client support so we can make direct calls into healthmon instead of chasing pointers and doing indirect calls v3: drag out of rfc status With a bit of luck, this should all go splendidly. Conflicts: This merge required an update on files: - fs/xfs/xfs_healthmon.c - fs/xfs/xfs_verify_media.c Such change was required because a parallel developement changed XFS header file xfs.h naming to xfs_platform.h, so the merge required to update those includes in both files above Signed-off-by: "Darrick J. Wong" <djwong@kernel.org> Signed-off-by: Carlos Maiolino <cem@kernel.org>
Why we want a copy of kernel headers in tools?
==============================================
There used to be no copies, with tools/ code using kernel headers
directly. From time to time tools/perf/ broke due to legitimate kernel
hacking. At some point Linus complained about such direct usage. Then we
adopted the current model.
The way these headers are used in perf are not restricted to just
including them to compile something.
There are sometimes used in scripts that convert defines into string
tables, etc, so some change may break one of these scripts, or new MSRs
may use some different #define pattern, etc.
E.g.:
$ ls -1 tools/perf/trace/beauty/*.sh | head -5
tools/perf/trace/beauty/arch_errno_names.sh
tools/perf/trace/beauty/drm_ioctl.sh
tools/perf/trace/beauty/fadvise.sh
tools/perf/trace/beauty/fsconfig.sh
tools/perf/trace/beauty/fsmount.sh
$
$ tools/perf/trace/beauty/fadvise.sh
static const char *fadvise_advices[] = {
[0] = "NORMAL",
[1] = "RANDOM",
[2] = "SEQUENTIAL",
[3] = "WILLNEED",
[4] = "DONTNEED",
[5] = "NOREUSE",
};
$
The tools/perf/check-headers.sh script, part of the tools/ build
process, points out changes in the original files.
So its important not to touch the copies in tools/ when doing changes in
the original kernel headers, that will be done later, when
check-headers.sh inform about the change to the perf tools hackers.
Another explanation from Ingo Molnar:
It's better than all the alternatives we tried so far:
- Symbolic links and direct #includes: this was the original approach but
was pushed back on from the kernel side, when tooling modified the
headers and broke them accidentally for kernel builds.
- Duplicate self-defined ABI headers like glibc: double the maintenance
burden, double the chance for mistakes, plus there's no tech-driven
notification mechanism to look at new kernel side changes.
What we are doing now is a third option:
- A software-enforced copy-on-write mechanism of kernel headers to
tooling, driven by non-fatal warnings on the tooling side build when
kernel headers get modified:
Warning: Kernel ABI header differences:
diff -u tools/include/uapi/drm/i915_drm.h include/uapi/drm/i915_drm.h
diff -u tools/include/uapi/linux/fs.h include/uapi/linux/fs.h
diff -u tools/include/uapi/linux/kvm.h include/uapi/linux/kvm.h
...
The tooling policy is to always pick up the kernel side headers as-is,
and integate them into the tooling build. The warnings above serve as a
notification to tooling maintainers that there's changes on the kernel
side.
We've been using this for many years now, and it might seem hacky, but
works surprisingly well.