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Yonghong Song says: ==================== bpf: Implement mprog API on top of existing cgroup progs 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 bpfchainer is a centralized approach and is not desirable as one of applications acts as a daemon. 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 5 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. Patches 4 and 5 add two tests to validate the implementation. [1] https://lore.kernel.org/r/20250224230116.283071-1-yonghong.song@linux.dev [2] https://lore.kernel.org/r/20230719140858.13224-2-daniel@iogearbox.net Changelogs: v4 -> v5: - v4: https://lore.kernel.org/bpf/20250530173812.1823479-1-yonghong.song@linux.dev/ - Remove early prog/link checking based flags and id_or_fd as later code will do checking as well. - Do proper cgroup flag checking for bpf_prog_attach(). v3 -> v4: - v3: https://lore.kernel.org/bpf/20250517162720.4077882-1-yonghong.song@linux.dev/ - Refactor some to make BPF_F_BEFORE/BPF_F_AFTER handling easier to understand. - Perviously, I degraded 'link' to 'prog' for later mprog handling. This is not correct. Similar to mprog.c, we should be check 'link' instead link->prog since it is possible two different links may have the same underlying prog and we do not want to miss supporting such use case. v2 -> v3: - v2: https://lore.kernel.org/bpf/20250508223524.487875-1-yonghong.song@linux.dev/ - Big change to replace get_anchor_prog() to get_prog_list() so the 'struct bpf_prog_list *' is returned directly. - Support 'BPF_F_BEFORE | BPF_F_AFTER' attachment if the prog list is empty and flags do not have 'BPF_F_LINK | BPF_F_ID' and id_or_fd is 0. - Add BPF_F_LINK support. - Patch 4 is added to reuse id_from_prog_fd() and id_from_link_fd(). v1 -> v2: - v1: https://lore.kernel.org/bpf/20250411011523.1838771-1-yonghong.song@linux.dev/ - Change cgroup_bpf.revisions from atomic64_t to u64. - Added missing bpf_prog_put in various places. - Rename get_cmp_prog() to get_anchor_prog(). The implementation tries to find the anchor prog regardless of whether id_or_fd is non-NULL or not. - Rename bpf_cgroup_prog_attached() to is_cgroup_prog_type() and handle BPF_PROG_TYPE_LSM properly (with BPF_LSM_CGROUP attach type). - I kept 'id || id_or_fd' condition as the condition 'id' is also used in mprog.c so I assume it is okay in cgroup.c as well. ==================== Link: https://patch.msgid.link/20250606163131.2428225-1-yonghong.song@linux.dev Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Linux kernel
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