Current cgroup prog ordering is appending at attachment time. This is not ideal. In some cases, users want specific ordering at a particular cgroup level. For example, in Meta, we have a case where three different applications all have cgroup/setsockopt progs and they require specific ordering. Current approach is to use a bpfchainer where one bpf prog contains multiple global functions and each global function can be freplaced by a prog for a specific application. The ordering of global functions decides the ordering of those application specific bpf progs. Using bpftrainer is a centralized approach and is not desirable as one of applications acts as a deamon. The decentralized attachment approach is more favorable for those applications. To address this, the existing mprog API ([2]) seems an ideal solution with supporting BPF_F_BEFORE and BPF_F_AFTER flags on top of existing cgroup bpf implementation. More specifically, the support is added for prog/link attachment with BPF_F_BEFORE and BPF_F_AFTER. The kernel mprog interface ([2]) is not used and the implementation is directly done in cgroup bpf code base. The mprog 'revision' is also implemented in attach/detach/replace, so users can query revision number to check the change of cgroup prog list. The patch set contains 4 patches. Patch 1 adds revision support for cgroup bpf progs. Patch 2 implements mprog API implementation for prog/link attach and revision update. Patch 3 adds a new libbpf API to do cgroup link attach with flags like BPF_F_BEFORE/BPF_F_AFTER. Patch 4 adds two tests to validate the implementation. [1] https://lore.kernel.org/r/20250224230116.283071-1-yonghong.song@xxxxxxxxx [2] https://lore.kernel.org/r/20230719140858.13224-2-daniel@xxxxxxxxxxxxx Yonghong Song (4): cgroup: Add bpf prog revisions to struct cgroup_bpf bpf: Implement mprog API on top of existing cgroup progs libbpf: Support link-based cgroup attach with options selftests/bpf: Add two selftests for mprog API based cgroup progs include/linux/bpf-cgroup-defs.h | 1 + include/uapi/linux/bpf.h | 7 + kernel/bpf/cgroup.c | 151 +++- kernel/bpf/syscall.c | 58 +- kernel/cgroup/cgroup.c | 5 +- tools/include/uapi/linux/bpf.h | 7 + tools/lib/bpf/bpf.c | 44 + tools/lib/bpf/bpf.h | 5 + tools/lib/bpf/libbpf.c | 28 + tools/lib/bpf/libbpf.h | 15 + tools/lib/bpf/libbpf.map | 1 + .../bpf/prog_tests/cgroup_mprog_opts.c | 752 ++++++++++++++++++ .../bpf/prog_tests/cgroup_mprog_ordering.c | 77 ++ .../selftests/bpf/progs/cgroup_mprog.c | 30 + 14 files changed, 1138 insertions(+), 43 deletions(-) create mode 100644 tools/testing/selftests/bpf/prog_tests/cgroup_mprog_opts.c create mode 100644 tools/testing/selftests/bpf/prog_tests/cgroup_mprog_ordering.c create mode 100644 tools/testing/selftests/bpf/progs/cgroup_mprog.c -- 2.47.1
