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117eab5c6e
Pull coredump updates from Christian Brauner:
"This contains an extension to the coredump socket and a proper rework
of the coredump code.
- This extends the coredump socket to allow the coredump server to
tell the kernel how to process individual coredumps. This allows
for fine-grained coredump management. Userspace can decide to just
let the kernel write out the coredump, or generate the coredump
itself, or just reject it.
* COREDUMP_KERNEL
The kernel will write the coredump data to the socket.
* COREDUMP_USERSPACE
The kernel will not write coredump data but will indicate to the
parent that a coredump has been generated. This is used when
userspace generates its own coredumps.
* COREDUMP_REJECT
The kernel will skip generating a coredump for this task.
* COREDUMP_WAIT
The kernel will prevent the task from exiting until the coredump
server has shutdown the socket connection.
The flexible coredump socket can be enabled by using the "@@"
prefix instead of the single "@" prefix for the regular coredump
socket:
@@/run/systemd/coredump.socket
- Cleanup the coredump code properly while we have to touch it
anyway.
Split out each coredump mode in a separate helper so it's easy to
grasp what is going on and make the code easier to follow. The core
coredump function should now be very trivial to follow"
* tag 'vfs-6.17-rc1.coredump' of git://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs: (31 commits)
cleanup: add a scoped version of CLASS()
coredump: add coredump_skip() helper
coredump: avoid pointless variable
coredump: order auto cleanup variables at the top
coredump: add coredump_cleanup()
coredump: auto cleanup prepare_creds()
cred: add auto cleanup method
coredump: directly return
coredump: auto cleanup argv
coredump: add coredump_write()
coredump: use a single helper for the socket
coredump: move pipe specific file check into coredump_pipe()
coredump: split pipe coredumping into coredump_pipe()
coredump: move core_pipe_count to global variable
coredump: prepare to simplify exit paths
coredump: split file coredumping into coredump_file()
coredump: rename do_coredump() to vfs_coredump()
selftests/coredump: make sure invalid paths are rejected
coredump: validate socket path in coredump_parse()
coredump: don't allow ".." in coredump socket path
...
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.