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Daniel Borkmann says: ==================== pull-request: bpf-next 2024-08-23 We've added 10 non-merge commits during the last 15 day(s) which contain a total of 10 files changed, 222 insertions(+), 190 deletions(-). The main changes are: 1) Add TCP_BPF_SOCK_OPS_CB_FLAGS to bpf_*sockopt() to address the case when long-lived sockets miss a chance to set additional callbacks if a sockops program was not attached early in their lifetime, from Alan Maguire. 2) Add a batch of BPF selftest improvements which fix a few bugs and add missing features to improve the test coverage of sockmap/sockhash, from Michal Luczaj. 3) Fix a false-positive Smatch-reported off-by-one in tcp_validate_cookie() which is part of the test_tcp_custom_syncookie BPF selftest, from Kuniyuki Iwashima. 4) Fix the flow_dissector BPF selftest which had a bug in IP header's tot_len calculation doing subtraction after htons() instead of inside htons(), from Asbjørn Sloth Tønnesen. * tag 'for-netdev' of https://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf-next: selftest: bpf: Remove mssind boundary check in test_tcp_custom_syncookie.c. selftests/bpf: Introduce __attribute__((cleanup)) in create_pair() selftests/bpf: Exercise SOCK_STREAM unix_inet_redir_to_connected() selftests/bpf: Honour the sotype of af_unix redir tests selftests/bpf: Simplify inet_socketpair() and vsock_socketpair_connectible() selftests/bpf: Socket pair creation, cleanups selftests/bpf: Support more socket types in create_pair() selftests/bpf: Avoid subtraction after htons() in ipip tests selftests/bpf: add sockopt tests for TCP_BPF_SOCK_OPS_CB_FLAGS bpf/bpf_get,set_sockopt: add option to set TCP-BPF sock ops flags ==================== Link: https://patch.msgid.link/20240823134959.1091-1-daniel@iogearbox.net Signed-off-by: Jakub Kicinski <kuba@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.