f5c79ffdc2
When switching network namespaces with the bpf_redirect_peer helper, the skb->mark and skb->tstamp fields are not zeroed out like they can be on a typical netns switch. This patch clarifies that in the helper description. Signed-off-by: Paul Chaignon <paul.chaignon@gmail.com> Acked-by: Daniel Borkmann <daniel@iogearbox.net> Acked-by: Martin KaFai Lau <martin.lau@kernel.org> Link: https://patch.msgid.link/ccc86af26d43c5c0b776bcba2601b7479c0d46d0.1746460653.git.paul.chaignon@gmail.com Signed-off-by: Jakub Kicinski <kuba@kernel.org> |
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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:
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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.
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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:
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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.