Commit 8d1608d7 authored by Kui-Feng Lee's avatar Kui-Feng Lee Committed by Martin KaFai Lau
Browse files

libbpf: Create a bpf_link in bpf_map__attach_struct_ops(). 



bpf_map__attach_struct_ops() was creating a dummy bpf_link as a
placeholder, but now it is constructing an authentic one by calling
bpf_link_create() if the map has the BPF_F_LINK flag.

You can flag a struct_ops map with BPF_F_LINK by calling
bpf_map__set_map_flags().

Signed-off-by: default avatarKui-Feng Lee <kuifeng@meta.com>
Acked-by: default avatarAndrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/r/20230323032405.3735486-5-kuifeng@meta.com


Signed-off-by: default avatarMartin KaFai Lau <martin.lau@kernel.org>
parent 68b04864

tools/lib/bpf/libbpf.c

+71 −24
Original line number Diff line number Diff line
@@ -116,6 +116,7 @@ static const char * const attach_type_name[] = { 
	[BPF_SK_REUSEPORT_SELECT_OR_MIGRATE]	= "sk_reuseport_select_or_migrate",

	[BPF_PERF_EVENT]		= "perf_event",

	[BPF_TRACE_KPROBE_MULTI]	= "trace_kprobe_multi",

	[BPF_STRUCT_OPS]		= "struct_ops",

};



static const char * const link_type_name[] = {
@@ -7686,6 +7687,37 @@ static int bpf_object__resolve_externs(struct bpf_object *obj, 
	return 0;

}



static void bpf_map_prepare_vdata(const struct bpf_map *map)

{

	struct bpf_struct_ops *st_ops;

	__u32 i;



	st_ops = map->st_ops;

	for (i = 0; i < btf_vlen(st_ops->type); i++) {

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

		void *kern_data;

		int prog_fd;



		if (!prog)

			continue;



		prog_fd = bpf_program__fd(prog);

		kern_data = st_ops->kern_vdata + st_ops->kern_func_off[i];

		*(unsigned long *)kern_data = prog_fd;

	}

}



static int bpf_object_prepare_struct_ops(struct bpf_object *obj)

{

	int i;



	for (i = 0; i < obj->nr_maps; i++)

		if (bpf_map__is_struct_ops(&obj->maps[i]))

			bpf_map_prepare_vdata(&obj->maps[i]);



	return 0;

}



static int bpf_object_load(struct bpf_object *obj, int extra_log_level, const char *target_btf_path)

{

	int err, i;
@@ -7711,6 +7743,7 @@ static int bpf_object_load(struct bpf_object *obj, int extra_log_level, const ch 
	err = err ? : bpf_object__relocate(obj, obj->btf_custom_path ? : target_btf_path);

	err = err ? : bpf_object__load_progs(obj, extra_log_level);

	err = err ? : bpf_object_init_prog_arrays(obj);

	err = err ? : bpf_object_prepare_struct_ops(obj);



	if (obj->gen_loader) {

		/* reset FDs */
@@ -11579,22 +11612,30 @@ struct bpf_link *bpf_program__attach(const struct bpf_program *prog) 
	return link;

}



struct bpf_link_struct_ops {

	struct bpf_link link;

	int map_fd;

};



static int bpf_link__detach_struct_ops(struct bpf_link *link)

{

	struct bpf_link_struct_ops *st_link;

	__u32 zero = 0;



	if (bpf_map_delete_elem(link->fd, &zero))

		return -errno;

	st_link = container_of(link, struct bpf_link_struct_ops, link);



	return 0;

	if (st_link->map_fd < 0)

		/* w/o a real link */

		return bpf_map_delete_elem(link->fd, &zero);



	return close(link->fd);

}



struct bpf_link *bpf_map__attach_struct_ops(const struct bpf_map *map)

{

	struct bpf_struct_ops *st_ops;

	struct bpf_link *link;

	__u32 i, zero = 0;

	int err;

	struct bpf_link_struct_ops *link;

	__u32 zero = 0;

	int err, fd;



	if (!bpf_map__is_struct_ops(map) || map->fd == -1)

		return libbpf_err_ptr(-EINVAL);
@@ -11603,31 +11644,37 @@ struct bpf_link *bpf_map__attach_struct_ops(const struct bpf_map *map) 
	if (!link)

		return libbpf_err_ptr(-EINVAL);



	st_ops = map->st_ops;

	for (i = 0; i < btf_vlen(st_ops->type); i++) {

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

		void *kern_data;

		int prog_fd;

	/* kern_vdata should be prepared during the loading phase. */

	err = bpf_map_update_elem(map->fd, &zero, map->st_ops->kern_vdata, 0);

	/* It can be EBUSY if the map has been used to create or

	 * update a link before.  We don't allow updating the value of

	 * a struct_ops once it is set.  That ensures that the value

	 * never changed.  So, it is safe to skip EBUSY.

	 */

	if (err && (!(map->def.map_flags & BPF_F_LINK) || err != -EBUSY)) {

		free(link);

		return libbpf_err_ptr(err);

	}



		if (!prog)

			continue;

	link->link.detach = bpf_link__detach_struct_ops;



		prog_fd = bpf_program__fd(prog);

		kern_data = st_ops->kern_vdata + st_ops->kern_func_off[i];

		*(unsigned long *)kern_data = prog_fd;

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

		/* w/o a real link */

		link->link.fd = map->fd;

		link->map_fd = -1;

		return &link->link;

	}



	err = bpf_map_update_elem(map->fd, &zero, st_ops->kern_vdata, 0);

	if (err) {

		err = -errno;

	fd = bpf_link_create(map->fd, 0, BPF_STRUCT_OPS, NULL);

	if (fd < 0) {

		free(link);

		return libbpf_err_ptr(err);

		return libbpf_err_ptr(fd);

	}



	link->detach = bpf_link__detach_struct_ops;

	link->fd = map->fd;

	link->link.fd = fd;

	link->map_fd = map->fd;



	return link;

	return &link->link;

}



typedef enum bpf_perf_event_ret (*bpf_perf_event_print_t)(struct perf_event_header *hdr,