Currently, the BPF cgroup iterator supports walking descendants in
either pre-order (BPF_CGROUP_ITER_DESCENDANTS_PRE) or post-order
(BPF_CGROUP_ITER_DESCENDANTS_POST). These modes perform an exhaustive
depth-first search (DFS) of the hierarchy. In scenarios where a BPF
program may need to inspect only the direct children of a given parent
cgroup, a full DFS is unnecessarily expensive.
This patch introduces a new BPF cgroup iterator control option,
BPF_CGROUP_ITER_CHILDREN. This control option restricts the traversal
to the immediate children of a specified parent cgroup, allowing for
more targeted and efficient iteration, particularly when exhaustive
depth-first search (DFS) traversal is not required.
Signed-off-by: Matt Bobrowski <mattbobrowski@google.com>
Link: https://lore.kernel.org/r/20260127085112.3608687-1-mattbobrowski@google.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
In some situations, if you fail to zero-initialize the
bpf_{prog,map,btf,link}_info structs supplied to the set of LIBBPF
helpers bpf_{prog,map,btf,link}_get_info_by_fd(), you can expect the
helper to return an error. This can possibly leave people in a
situation where they're scratching their heads for an unnnecessary
amount of time. Make an explicit remark about the requirement of
zero-initializing the supplied bpf_{prog,map,btf,link}_info structs
for the respective LIBBPF helpers.
Internally, LIBBPF helpers bpf_{prog,map,btf,link}_get_info_by_fd()
call into bpf_obj_get_info_by_fd() where the bpf(2)
BPF_OBJ_GET_INFO_BY_FD command is used. This specific command is
effectively backed by restrictions enforced by the
bpf_check_uarg_tail_zero() helper. This function ensures that if the
size of the supplied bpf_{prog,map,btf,link}_info structs are larger
than what the kernel can handle, trailing bits are zeroed. This can be
a problem when compiling against UAPI headers that don't necessarily
match the sizes of the same underlying types known to the kernel.
Signed-off-by: Matt Bobrowski <mattbobrowski@google.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Acked-by: Jiri Olsa <jolsa@kernel.org>
Link: https://lore.kernel.org/bpf/ZcyEb8x4VbhieWsL@google.com
Matt Bobrowski