[RFC PATCH bpf-next 00/12] bpf: A common way to attach struct_ops to a cgroup

[Martin KaFai Lau <martin.lau@linux.dev>]

From: Martin KaFai Lau <martin.lau@kernel.org>

At LSF/MM/BPF 2025, I presented [1] the need for a new interface
to extend tcp_sock operations instead of adding more
BPF_SOCK_OPS_*CB enum values. The need for predictable ordering when
attaching struct_ops to a cgroup was also briefly discussed.

At LSF/MM/BPF 2026, additional use cases were raised, in particular
OOM and memcg use cases, that also need to attach struct_ops to a
cgroup.

BPF already has a common bpf_link-based API for attaching different
BPF program types to a cgroup. It provides common attach, detach,
update, ordering, and query semantics across those program types.

This series extends the same model to struct_ops. Conceptually,
struct_ops is a group of BPF programs, so using similar
attachment/detachment/update/query APIs and ordering semantics for
cgroup attachment keeps the interface consistent with existing cgroup
BPF links.

This series uses a new struct bpf_tcp_ops as the first user. Not all
BPF_SOCK_OPS_*CB callbacks are implemented yet.

The selftests cover the basic attach, query, and ordering behavior.
More coverage is still needed for multi-level cgroup inheritance,
BPF_F_BEFORE/AFTER, and bpf_link__update_map().

The map_free_pre_rcu addition in patch 2 is not very ideal, this
will need some thoughts also.

[1] page 13: https://drive.google.com/file/d/1wjKZth6T0llLJ_ONPAL_6Q_jbxbAjByp/view?usp=sharing

Martin KaFai Lau (12):
  bpf: Remove __rcu tagging in st_link->map
  bpf: Make struct_ops tasks_rcu grace period optional
  bpf: Add bpf_struct_ops accessor helpers
  bpf: Remove unnecessary prog_list_prog() check
  bpf: Replace prog_list_prog() check with direct pl->prog and pl->link check
  bpf: Add prog_list_init_item(), prog_list_replace_item(), and prog_list_id()
  bpf: Move LSM trampoline unlink into bpf_cgroup_link_auto_detach()
  bpf: Add a few bpf_cgroup_array_* helper functions
  bpf: Add infrastructure to support attaching struct_ops to cgroups
  bpf: tcp: Support selected sock_ops callbacks as struct_ops
  libbpf: Support attaching struct_ops to a cgroup
  selftests/bpf: Test attaching struct_ops to a cgroup

 include/linux/bpf-cgroup-defs.h               |   1 +
 include/linux/bpf-cgroup.h                    |  28 ++
 include/linux/bpf.h                           |  55 ++-
 include/net/tcp.h                             |  74 ++-
 include/uapi/linux/bpf.h                      |   4 +-
 kernel/bpf/bpf_struct_ops.c                   | 152 ++++--
 kernel/bpf/btf.c                              |  23 +-
 kernel/bpf/cgroup.c                           | 452 ++++++++++++++++--
 kernel/bpf/core.c                             |   5 +
 kernel/bpf/syscall.c                          |   4 +
 net/ipv4/Makefile                             |   1 +
 net/ipv4/af_inet.c                            |   1 +
 net/ipv4/bpf_tcp_ca.c                         |  16 +
 net/ipv4/bpf_tcp_ops.c                        | 134 ++++++
 net/ipv4/tcp.c                                |   4 +-
 net/ipv4/tcp_output.c                         |   5 +-
 tools/include/uapi/linux/bpf.h                |   4 +-
 tools/lib/bpf/bpf.c                           |   2 +
 tools/lib/bpf/bpf.h                           |   3 +-
 tools/lib/bpf/libbpf.c                        |  59 +++
 tools/lib/bpf/libbpf.h                        |   3 +
 tools/lib/bpf/libbpf.map                      |   5 +
 tools/lib/bpf/libbpf_version.h                |   2 +-
 .../selftests/bpf/prog_tests/bpf_tcp_ops.c    | 207 ++++++++
 .../testing/selftests/bpf/progs/bpf_tcp_ops.c |  97 ++++
 25 files changed, 1253 insertions(+), 88 deletions(-)
 create mode 100644 net/ipv4/bpf_tcp_ops.c
 create mode 100644 tools/testing/selftests/bpf/prog_tests/bpf_tcp_ops.c
 create mode 100644 tools/testing/selftests/bpf/progs/bpf_tcp_ops.c

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2.53.0-Meta