[PATCH bpf-next v2 0/3] bpf: expose cgroup preorder attachment state to userspace

[Hui Su]

Commit 4b82b181a26c ("bpf: Allow pre-ordering for bpf cgroup progs")
introduced BPF_F_PREORDER to request top-down (ancestor to descendant)
execution ordering across the cgroup hierarchy. While this flag is stored
in struct bpf_prog_list::flags and affects the effective program ordering,
direct BPF_PROG_QUERY currently reports only the cgroup-wide flags and
omits BPF_F_PREORDER from prog_attach_flags[].

This series extends direct cgroup program queries to expose the per-program
BPF_F_PREORDER state, adds selftests to validate the reported flags, and
updates bpftool to support inspection, attachment, documentation, and bash
completion.

Structure of the series:
- Patch 1 extends __cgroup_bpf_query() so that prog_attach_flags[] includes
  BPF_F_PREORDER for direct queries.
- Patch 2 adds query verification to cgroup_mprog_opts selftests for both
  direct program and bpf_link attachments.
- Patch 3 updates bpftool with bitmask attach flag formatting, preorder
  attachment CLI support, bash completion for valid flag combinations,
  and documentation.

Testing:
- Verified that baseline kernel reports 0x2 for PREORDER multi-attachments
  through BPF_PROG_QUERY.
- Verified that the patched kernel reports 0x42 (BPF_F_ALLOW_MULTI |
  BPF_F_PREORDER).
- Selftests cgroup_mprog_opts (all subtests) and cgroup_preorder pass in an
  x86_64 QEMU/KVM guest.
- bpftool and its documentation build cleanly without warnings or errors.
- Bash completion verified for standalone and composite flag combinations.
- checkpatch.pl reports 0 errors and 0 warnings across all patches.

Changes in v2:
- Rebase onto bpf-next and drop the Fixes tag, as requested by
  Alexei Starovoitov.
- Document the userspace-visible BPF_PROG_QUERY flag extension.
- Factor the duplicated PREORDER query checks and fix comment style.
- Clarify PREORDER ordering and single/multi attachment semantics.
- Fix bash completion for valid PREORDER flag combinations.

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  | 25 ++++---
 tools/bpf/bpftool/bash-completion/bpftool     |  4 +-
 tools/bpf/bpftool/cgroup.c                    | 55 +++++++++-----
 .../bpf/prog_tests/cgroup_mprog_opts.c        | 72 ++++++++++++++++++-
 5 files changed, 134 insertions(+), 38 deletions(-)

-- 
2.55.0