Commit d66562fb authored by Andrii Nakryiko's avatar Andrii Nakryiko Committed by Alexei Starovoitov
Browse files

libbpf: Add BPF object skeleton support 



Add new set of APIs, allowing to open/load/attach BPF object through BPF
object skeleton, generated by bpftool for a specific BPF object file. All the
xxx_skeleton() APIs wrap up corresponding bpf_object_xxx() APIs, but
additionally also automate map/program lookups by name, global data
initialization and mmap()-ing, etc.  All this greatly improves and simplifies
userspace usability of working with BPF programs. See follow up patches for
examples.

Signed-off-by: default avatarAndrii Nakryiko <andriin@fb.com>
Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
Acked-by: default avatarMartin KaFai Lau <kafai@fb.com>
Link: https://lore.kernel.org/bpf/20191214014341.3442258-13-andriin@fb.com
parent 3f519353

tools/lib/bpf/libbpf.c

+162 −0
Original line number Diff line number Diff line
@@ -6793,3 +6793,165 @@ int libbpf_num_possible_cpus(void) 
	WRITE_ONCE(cpus, tmp_cpus);

	return tmp_cpus;

}



int bpf_object__open_skeleton(struct bpf_object_skeleton *s,

			      const struct bpf_object_open_opts *opts)

{

	DECLARE_LIBBPF_OPTS(bpf_object_open_opts, skel_opts,

		.object_name = s->name,

	);

	struct bpf_object *obj;

	int i;



	/* Attempt to preserve opts->object_name, unless overriden by user

	 * explicitly. Overwriting object name for skeletons is discouraged,

	 * as it breaks global data maps, because they contain object name

	 * prefix as their own map name prefix. When skeleton is generated,

	 * bpftool is making an assumption that this name will stay the same.

	 */

	if (opts) {

		memcpy(&skel_opts, opts, sizeof(*opts));

		if (!opts->object_name)

			skel_opts.object_name = s->name;

	}



	obj = bpf_object__open_mem(s->data, s->data_sz, &skel_opts);

	if (IS_ERR(obj)) {

		pr_warn("failed to initialize skeleton BPF object '%s': %ld\n",

			s->name, PTR_ERR(obj));

		return PTR_ERR(obj);

	}



	*s->obj = obj;



	for (i = 0; i < s->map_cnt; i++) {

		struct bpf_map **map = s->maps[i].map;

		const char *name = s->maps[i].name;

		void **mmaped = s->maps[i].mmaped;



		*map = bpf_object__find_map_by_name(obj, name);

		if (!*map) {

			pr_warn("failed to find skeleton map '%s'\n", name);

			return -ESRCH;

		}



		if (mmaped)

			*mmaped = (*map)->mmaped;

	}



	for (i = 0; i < s->prog_cnt; i++) {

		struct bpf_program **prog = s->progs[i].prog;

		const char *name = s->progs[i].name;



		*prog = bpf_object__find_program_by_name(obj, name);

		if (!*prog) {

			pr_warn("failed to find skeleton program '%s'\n", name);

			return -ESRCH;

		}

	}



	return 0;

}



int bpf_object__load_skeleton(struct bpf_object_skeleton *s)

{

	int i, err;



	err = bpf_object__load(*s->obj);

	if (err) {

		pr_warn("failed to load BPF skeleton '%s': %d\n", s->name, err);

		return err;

	}



	for (i = 0; i < s->map_cnt; i++) {

		struct bpf_map *map = *s->maps[i].map;

		size_t mmap_sz = bpf_map_mmap_sz(map);

		int prot, map_fd = bpf_map__fd(map);

		void **mmaped = s->maps[i].mmaped;

		void *remapped;



		if (!mmaped)

			continue;



		if (!(map->def.map_flags & BPF_F_MMAPABLE)) {

			*mmaped = NULL;

			continue;

		}



		if (map->def.map_flags & BPF_F_RDONLY_PROG)

			prot = PROT_READ;

		else

			prot = PROT_READ | PROT_WRITE;



		/* Remap anonymous mmap()-ed "map initialization image" as

		 * a BPF map-backed mmap()-ed memory, but preserving the same

		 * memory address. This will cause kernel to change process'

		 * page table to point to a different piece of kernel memory,

		 * but from userspace point of view memory address (and its

		 * contents, being identical at this point) will stay the

		 * same. This mapping will be released by bpf_object__close()

		 * as per normal clean up procedure, so we don't need to worry

		 * about it from skeleton's clean up perspective.

		 */

		remapped = mmap(*mmaped, mmap_sz, prot, MAP_SHARED | MAP_FIXED,

				map_fd, 0);

		if (remapped == MAP_FAILED) {

			err = -errno;

			*mmaped = NULL;

			pr_warn("failed to re-mmap() map '%s': %d\n",

				 bpf_map__name(map), err);

			return err;

		}

	}



	return 0;

}



int bpf_object__attach_skeleton(struct bpf_object_skeleton *s)

{

	int i;



	for (i = 0; i < s->prog_cnt; i++) {

		struct bpf_program *prog = *s->progs[i].prog;

		struct bpf_link **link = s->progs[i].link;

		const struct bpf_sec_def *sec_def;

		const char *sec_name = bpf_program__title(prog, false);



		sec_def = find_sec_def(sec_name);

		if (!sec_def || !sec_def->attach_fn)

			continue;



		*link = sec_def->attach_fn(sec_def, prog);

		if (IS_ERR(*link)) {

			pr_warn("failed to auto-attach program '%s': %ld\n",

				bpf_program__name(prog), PTR_ERR(*link));

			return PTR_ERR(*link);

		}

	}



	return 0;

}



void bpf_object__detach_skeleton(struct bpf_object_skeleton *s)

{

	int i;



	for (i = 0; i < s->prog_cnt; i++) {

		struct bpf_link **link = s->progs[i].link;



		if (!IS_ERR_OR_NULL(*link))

			bpf_link__destroy(*link);

		*link = NULL;

	}

}



void bpf_object__destroy_skeleton(struct bpf_object_skeleton *s)

{

	if (s->progs)

		bpf_object__detach_skeleton(s);

	if (s->obj)

		bpf_object__close(*s->obj);

	free(s->maps);

	free(s->progs);

	free(s);

}

tools/lib/bpf/libbpf.h

+38 −0
Original line number Diff line number Diff line
@@ -631,6 +631,44 @@ BPF_EMBED_OBJ_DECLARE(NAME) 
#define BPF_EMBED_OBJ(NAME, PATH) __BPF_EMBED_OBJ(NAME, PATH, 16, ".quad")

#endif



struct bpf_map_skeleton {

	const char *name;

	struct bpf_map **map;

	void **mmaped;

};



struct bpf_prog_skeleton {

	const char *name;

	struct bpf_program **prog;

	struct bpf_link **link;

};



struct bpf_object_skeleton {

	size_t sz; /* size of this struct, for forward/backward compatibility */



	const char *name;

	void *data;

	size_t data_sz;



	struct bpf_object **obj;



	int map_cnt;

	int map_skel_sz; /* sizeof(struct bpf_skeleton_map) */

	struct bpf_map_skeleton *maps;



	int prog_cnt;

	int prog_skel_sz; /* sizeof(struct bpf_skeleton_prog) */

	struct bpf_prog_skeleton *progs;

};



LIBBPF_API int

bpf_object__open_skeleton(struct bpf_object_skeleton *s,

			  const struct bpf_object_open_opts *opts);

LIBBPF_API int bpf_object__load_skeleton(struct bpf_object_skeleton *s);

LIBBPF_API int bpf_object__attach_skeleton(struct bpf_object_skeleton *s);

LIBBPF_API void bpf_object__detach_skeleton(struct bpf_object_skeleton *s);

LIBBPF_API void bpf_object__destroy_skeleton(struct bpf_object_skeleton *s);



#ifdef __cplusplus

} /* extern "C" */

#endif

tools/lib/bpf/libbpf.map

+5 −0
Original line number Diff line number Diff line
@@ -213,6 +213,11 @@ LIBBPF_0.0.7 { 
	global:

		btf_dump__emit_type_decl;

		bpf_object__find_program_by_name;

		bpf_object__attach_skeleton;

		bpf_object__destroy_skeleton;

		bpf_object__detach_skeleton;

		bpf_object__load_skeleton;

		bpf_object__open_skeleton;

		bpf_program__attach;

		bpf_program__name;

		btf__align_of;

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