[PATCH bpf 0/3] bpf: expose cgroup preorder attachment state to userspace

[Hui Su <sh_def@163.com>]

Commit 4b82b181a26c ("bpf: Allow pre-ordering for bpf cgroup progs")
introduced BPF_F_PREORDER to request pre-order execution across the
cgroup hierarchy. While the kernel records BPF_F_PREORDER in pl->flags,
__cgroup_bpf_query() currently fails to report it to user space in
prog_attach_flags[] during direct cgroup program queries.

This series fixes the kernel query path, extends BPF selftests to
verify the fix, and updates bpftool to recognize and format the
BPF_F_PREORDER flag.

Patch 1 fixes __cgroup_bpf_query() to merge (pl->flags & BPF_F_PREORDER)
with cgroup flags when copying per-program attach flags to user space.

Patch 2 extends selftests/bpf (cgroup_mprog_opts) to verify that direct
and link queries report BPF_F_PREORDER (0x42), matching programs by
prog_id with guarded failure paths.

Patch 3 adds bpftool support: a bitmask flags formatter for cgroup show,
support for "preorder" in cgroup attach, documentation updates, and bash
completion.

Testing:
- Verified on unpatched kernel: selftest reproduces failure
  (actual 2 != expected 66).
- Verified on patched kernel (bpf/master): both cgroup_mprog_opts and
  cgroup_preorder pass 100% in QEMU guest environment.
- Verified bpftool build, format unit tests, and checkpatch
  (0 errors, 0 warnings).

Hui Su (3):
  bpf: Report BPF_F_PREORDER in cgroup program queries
  selftests/bpf: Test querying BPF_F_PREORDER cgroup attachments
  bpftool: Add support for BPF_F_PREORDER cgroup attach flag

 kernel/bpf/cgroup.c                           | 16 ++--
 .../bpftool/Documentation/bpftool-cgroup.rst  |  9 +-
 tools/bpf/bpftool/bash-completion/bpftool     |  2 +-
 tools/bpf/bpftool/cgroup.c                    | 55 +++++++----
 .../bpf/prog_tests/cgroup_mprog_opts.c        | 94 ++++++++++++++++++-
 5 files changed, 144 insertions(+), 32 deletions(-)

-- 
2.55.0