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dd466ea002
Pull vfs error reporting updates from Christian Brauner: "This contains the changes to support generic I/O error reporting. Filesystems currently have no standard mechanism for reporting metadata corruption and file I/O errors to userspace via fsnotify. Each filesystem (xfs, ext4, erofs, f2fs, etc.) privately defines EFSCORRUPTED, and error reporting to fanotify is inconsistent or absent entirely. This introduces a generic fserror infrastructure built around struct super_block that gives filesystems a standard way to queue metadata and file I/O error reports for delivery to fsnotify. Errors are queued via mempools and queue_work to avoid holding filesystem locks in the notification path; unmount waits for pending events to drain. A new super_operations::report_error callback lets filesystem drivers respond to file I/O errors themselves (to be used by an upcoming XFS self-healing patchset). On the uapi side, EFSCORRUPTED and EUCLEAN are promoted from private per-filesystem definitions to canonical errno.h values across all architectures" * tag 'vfs-7.0-rc1.fserror' of git://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs: ext4: convert to new fserror helpers xfs: translate fsdax media errors into file "data lost" errors when convenient xfs: report fs metadata errors via fsnotify iomap: report file I/O errors to the VFS fs: report filesystem and file I/O errors to fsnotify uapi: promote EFSCORRUPTED and EUCLEAN to errno.h
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.