Commit cc4f864b authored by Andrii Nakryiko's avatar Andrii Nakryiko Committed by Alexei Starovoitov
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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: default avatarAndrii Nakryiko <andriin@fb.com>
Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20200330030001.2312810-4-andriin@fb.com
parent 0c991ebc

tools/include/uapi/linux/bpf.h

+12 −0
Original line number Diff line number Diff line
@@ -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

tools/lib/bpf/bpf.c

+34 −0
Original line number Diff line number Diff line
@@ -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)

{

tools/lib/bpf/bpf.h

+19 −0
Original line number Diff line number Diff line
@@ -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;

tools/lib/bpf/libbpf.c

+46 −0
Original line number Diff line number Diff line
@@ -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;

tools/lib/bpf/libbpf.h

+7 −1
Original line number Diff line number Diff line
@@ -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;



/*

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