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libbpf: Add support for bpf_link-based cgroup attachment 

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
alistair/sensors
Andrii Nakryiko 2020-03-29 20:00:00 -07:00 committed by Alexei Starovoitov
parent 0c991ebc8c
commit cc4f864bb1
6 changed files with 122 additions and 1 deletions
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12
tools/include/uapi/linux/bpf.h
View File

@ -112,6 +112,7 @@ enum bpf_cmd {
BPF_MAP_UPDATE_BATCH,
BPF_MAP_DELETE_BATCH,
BPF_LINK_CREATE,
BPF_LINK_UPDATE,
};
enum bpf_map_type {
@ -577,6 +578,17 @@ union bpf_attr {
__u32 attach_type; /* attach type */
__u32 flags; /* extra flags */
} link_create;
struct { /* struct used by BPF_LINK_UPDATE command */
__u32 link_fd; /* link fd */
/* new program fd to update link with */
__u32 new_prog_fd;
__u32 flags; /* extra flags */
/* expected link's program fd; is specified only if
* BPF_F_REPLACE flag is set in flags */
__u32 old_prog_fd;
} link_update;
} __attribute__((aligned(8)));
/* The description below is an attempt at providing documentation to eBPF

34
tools/lib/bpf/bpf.c
View File

@ -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)
{

19
tools/lib/bpf/bpf.h
View File

@ -168,6 +168,25 @@ LIBBPF_API int bpf_prog_detach(int attachable_fd, enum bpf_attach_type type);
LIBBPF_API int bpf_prog_detach2(int prog_fd, int attachable_fd,
enum bpf_attach_type type);
struct bpf_link_create_opts {
size_t sz; /* size of this struct for forward/backward compatibility */
};
#define bpf_link_create_opts__last_field sz
LIBBPF_API int bpf_link_create(int prog_fd, int target_fd,
enum bpf_attach_type attach_type,
const struct bpf_link_create_opts *opts);
struct bpf_link_update_opts {
size_t sz; /* size of this struct for forward/backward compatibility */
__u32 flags; /* extra flags */
__u32 old_prog_fd; /* expected old program FD */
};
#define bpf_link_update_opts__last_field old_prog_fd
LIBBPF_API int bpf_link_update(int link_fd, int new_prog_fd,
const struct bpf_link_update_opts *opts);
struct bpf_prog_test_run_attr {
int prog_fd;
int repeat;

46
tools/lib/bpf/libbpf.c
View File

@ -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;

8
tools/lib/bpf/libbpf.h
View File

@ -224,6 +224,8 @@ LIBBPF_API int bpf_link__fd(const struct bpf_link *link);
LIBBPF_API const char *bpf_link__pin_path(const struct bpf_link *link);
LIBBPF_API int bpf_link__pin(struct bpf_link *link, const char *path);
LIBBPF_API int bpf_link__unpin(struct bpf_link *link);
LIBBPF_API int bpf_link__update_program(struct bpf_link *link,
struct bpf_program *prog);
LIBBPF_API void bpf_link__disconnect(struct bpf_link *link);
LIBBPF_API int bpf_link__destroy(struct bpf_link *link);
@ -245,13 +247,17 @@ bpf_program__attach_tracepoint(struct bpf_program *prog,
LIBBPF_API struct bpf_link *
bpf_program__attach_raw_tracepoint(struct bpf_program *prog,
const char *tp_name);
LIBBPF_API struct bpf_link *
bpf_program__attach_trace(struct bpf_program *prog);
LIBBPF_API struct bpf_link *
bpf_program__attach_lsm(struct bpf_program *prog);
LIBBPF_API struct bpf_link *
bpf_program__attach_cgroup(struct bpf_program *prog, int cgroup_fd);
struct bpf_map;
LIBBPF_API struct bpf_link *bpf_map__attach_struct_ops(struct bpf_map *map);
struct bpf_insn;
/*

4
tools/lib/bpf/libbpf.map
View File

@ -243,7 +243,11 @@ LIBBPF_0.0.8 {
bpf_link__pin;
bpf_link__pin_path;
bpf_link__unpin;
bpf_link__update_program;
bpf_link_create;
bpf_link_update;
bpf_map__set_initial_value;
bpf_program__attach_cgroup;
bpf_program__attach_lsm;
bpf_program__is_lsm;
bpf_program__set_attach_target;