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2f2d529458
Pull bitmap updates from Yury Norov:
- cpumask_next_wrap() rework (me)
- GENMASK() simplification (I Hsin)
- rust bindings for cpumasks (Viresh and me)
- scattered cleanups (Andy, Tamir, Vincent, Ignacio and Joel)
* tag 'bitmap-for-6.15' of https://github.com/norov/linux: (22 commits)
cpumask: align text in comment
riscv: fix test_and_{set,clear}_bit ordering documentation
treewide: fix typo 'unsigned __init128' -> 'unsigned __int128'
MAINTAINERS: add rust bindings entry for bitmap API
rust: Add cpumask helpers
uapi: Revert "bitops: avoid integer overflow in GENMASK(_ULL)"
cpumask: drop cpumask_next_wrap_old()
PCI: hv: Switch hv_compose_multi_msi_req_get_cpu() to using cpumask_next_wrap()
scsi: lpfc: rework lpfc_next_{online,present}_cpu()
scsi: lpfc: switch lpfc_irq_rebalance() to using cpumask_next_wrap()
s390: switch stop_machine_yield() to using cpumask_next_wrap()
padata: switch padata_find_next() to using cpumask_next_wrap()
cpumask: use cpumask_next_wrap() where appropriate
cpumask: re-introduce cpumask_next{,_and}_wrap()
cpumask: deprecate cpumask_next_wrap()
powerpc/xmon: simplify xmon_batch_next_cpu()
ibmvnic: simplify ibmvnic_set_queue_affinity()
virtio_net: simplify virtnet_set_affinity()
objpool: rework objpool_pop()
cpumask: add for_each_{possible,online}_cpu_wrap
...
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.