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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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46
src/libbpf.c
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@@ -6978,6 +6978,12 @@ struct bpf_link {
bool disconnected;
};
/* Replace link's underlying BPF program with the new one */
int bpf_link__update_program(struct bpf_link *link, struct bpf_program *prog)
{
return bpf_link_update(bpf_link__fd(link), bpf_program__fd(prog), NULL);
}
/* Release "ownership" of underlying BPF resource (typically, BPF program
* attached to some BPF hook, e.g., tracepoint, kprobe, etc). Disconnected
* link, when destructed through bpf_link__destroy() call won't attempt to
@@ -7533,6 +7539,46 @@ static struct bpf_link *attach_lsm(const struct bpf_sec_def *sec,
return bpf_program__attach_lsm(prog);
}
struct bpf_link *
bpf_program__attach_cgroup(struct bpf_program *prog, int cgroup_fd)
{
const struct bpf_sec_def *sec_def;
enum bpf_attach_type attach_type;
char errmsg[STRERR_BUFSIZE];
struct bpf_link *link;
int prog_fd, link_fd;
prog_fd = bpf_program__fd(prog);
if (prog_fd < 0) {
pr_warn("program '%s': can't attach before loaded\n",
bpf_program__title(prog, false));
return ERR_PTR(-EINVAL);
}
link = calloc(1, sizeof(*link));
if (!link)
return ERR_PTR(-ENOMEM);
link->detach = &bpf_link__detach_fd;
attach_type = bpf_program__get_expected_attach_type(prog);
if (!attach_type) {
sec_def = find_sec_def(bpf_program__title(prog, false));
if (sec_def)
attach_type = sec_def->attach_type;
}
link_fd = bpf_link_create(prog_fd, cgroup_fd, attach_type, NULL);
if (link_fd < 0) {
link_fd = -errno;
free(link);
pr_warn("program '%s': failed to attach to cgroup: %s\n",
bpf_program__title(prog, false),
libbpf_strerror_r(link_fd, errmsg, sizeof(errmsg)));
return ERR_PTR(link_fd);
}
link->fd = link_fd;
return link;
}
struct bpf_link *bpf_program__attach(struct bpf_program *prog)
{
const struct bpf_sec_def *sec_def;