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libbpf: Add support for bpf_link-based cgroup attachment

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Add bpf_program__attach_cgroup(), which uses BPF_LINK_CREATE subcommand to
create an FD-based kernel bpf_link. Also add low-level bpf_link_create() API.

If expected_attach_type is not specified explicitly with
bpf_program__set_expected_attach_type(), libbpf will try to determine proper
attach type from BPF program's section definition.

Also add support for bpf_link's underlying BPF program replacement:
  - unconditional through high-level bpf_link__update_program() API;
  - cmpxchg-like with specifying expected current BPF program through
    low-level bpf_link_update() API.

Signed-off-by: Andrii Nakryiko <andriin@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20200330030001.2312810-4-andriin@fb.com
This commit is contained in:
Andrii Nakryiko
2020-03-29 20:00:00 -07:00
committed by Andrii Nakryiko
parent 8b41602694
commit 1543a19f36
6 changed files with 122 additions and 1 deletions
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34
src/bpf.c
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@@ -585,6 +585,40 @@ int bpf_prog_detach2(int prog_fd, int target_fd, enum bpf_attach_type type)
return sys_bpf(BPF_PROG_DETACH, &attr, sizeof(attr));
}
int bpf_link_create(int prog_fd, int target_fd,
enum bpf_attach_type attach_type,
const struct bpf_link_create_opts *opts)
{
union bpf_attr attr;
if (!OPTS_VALID(opts, bpf_link_create_opts))
return -EINVAL;
memset(&attr, 0, sizeof(attr));
attr.link_create.prog_fd = prog_fd;
attr.link_create.target_fd = target_fd;
attr.link_create.attach_type = attach_type;
return sys_bpf(BPF_LINK_CREATE, &attr, sizeof(attr));
}
int bpf_link_update(int link_fd, int new_prog_fd,
const struct bpf_link_update_opts *opts)
{
union bpf_attr attr;
if (!OPTS_VALID(opts, bpf_link_update_opts))
return -EINVAL;
memset(&attr, 0, sizeof(attr));
attr.link_update.link_fd = link_fd;
attr.link_update.new_prog_fd = new_prog_fd;
attr.link_update.flags = OPTS_GET(opts, flags, 0);
attr.link_update.old_prog_fd = OPTS_GET(opts, old_prog_fd, 0);
return sys_bpf(BPF_LINK_UPDATE, &attr, sizeof(attr));
}
int bpf_prog_query(int target_fd, enum bpf_attach_type type, __u32 query_flags,
__u32 *attach_flags, __u32 *prog_ids, __u32 *prog_cnt)
{