[PATCH bpf-next 0/3] bpf: expose bpf_{g,s}et_retval to more cgroup hooks

[Stanislav Fomichev <sdf@google.com>]

Apparently, only a small subset of cgroup hooks actually falls
back to cgroup_base_func_proto. This leads to unexpected result
where not all cgroup helpers have bpf_{g,s}et_retval.

It's getting harder and harder to manage which helpers are exported
to which hooks. We now have the following call chains:

- cg_skb_func_proto
  - sk_filter_func_proto
    - bpf_sk_base_func_proto
      - bpf_base_func_proto

So by looking at cg_skb_func_proto it's pretty hard to understand
what's going on.

For cgroup helpers, I'm proposing we do the following instead:

  func_proto = cgroup_common_func_proto();
  if (func_proto) return func_proto;

  /* optional, if hook has 'current' */
  func_proto = cgroup_current_func_proto();
  if (func_proto) return func_proto;

  ...

  switch (func_id) {
  /* hook specific helpers */
  case BPF_FUNC_hook_specific_helper:
    return &xyz;
  default:
    /* always fall back to plain bpf_base_func_proto */
    bpf_base_func_proto(func_id);
  }

If this turns out more workable, we can follow up with converting
the rest to the same pattern.

Stanislav Fomichev (3):
  bpf: introduce cgroup_{common,current}_func_proto
  bpf: use cgroup_{common,current}_func_proto in more hooks
  selftests/bpf: make sure bpf_{g,s}et_retval is exposed everywhere

 include/linux/bpf.h                           | 16 +++
 kernel/bpf/cgroup.c                           | 82 +++++++--------
 kernel/bpf/helpers.c                          | 99 ++++++++++++++++++-
 net/core/filter.c                             | 78 ++++++---------
 tools/testing/selftests/bpf/Makefile          |  1 +
 .../bpf/cgroup_getset_retval_hooks.h          | 25 +++++
 .../bpf/prog_tests/cgroup_getset_retval.c     | 48 +++++++++
 .../bpf/progs/cgroup_getset_retval_hooks.c    | 16 +++
 8 files changed, 270 insertions(+), 95 deletions(-)
 create mode 100644 tools/testing/selftests/bpf/cgroup_getset_retval_hooks.h
 create mode 100644 tools/testing/selftests/bpf/progs/cgroup_getset_retval_hooks.c

-- 
2.37.1.595.g718a3a8f04-goog