Commit 912dd4b0 authored by Kui-Feng Lee's avatar Kui-Feng Lee Committed by Martin KaFai Lau
Browse files

libbpf: Update a bpf_link with another struct_ops. 



Introduce bpf_link__update_map(), which allows to atomically update
underlying struct_ops implementation for given struct_ops BPF link.

Also add old_map_fd to struct bpf_link_update_opts to handle
BPF_F_REPLACE feature.

Signed-off-by: default avatarKui-Feng Lee <kuifeng@meta.com>
Link: https://lore.kernel.org/r/20230323032405.3735486-7-kuifeng@meta.com


Signed-off-by: default avatarMartin KaFai Lau <martin.lau@kernel.org>
parent aef56f2e

tools/lib/bpf/bpf.c

+7 −1
Original line number Diff line number Diff line
@@ -794,11 +794,17 @@ int bpf_link_update(int link_fd, int new_prog_fd, 
	if (!OPTS_VALID(opts, bpf_link_update_opts))

		return libbpf_err(-EINVAL);



	if (OPTS_GET(opts, old_prog_fd, 0) && OPTS_GET(opts, old_map_fd, 0))

		return libbpf_err(-EINVAL);



	memset(&attr, 0, attr_sz);

	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);

	if (OPTS_GET(opts, old_prog_fd, 0))

		attr.link_update.old_prog_fd = OPTS_GET(opts, old_prog_fd, 0);

	else if (OPTS_GET(opts, old_map_fd, 0))

		attr.link_update.old_map_fd = OPTS_GET(opts, old_map_fd, 0);



	ret = sys_bpf(BPF_LINK_UPDATE, &attr, attr_sz);

	return libbpf_err_errno(ret);

tools/lib/bpf/bpf.h

+2 −1
Original line number Diff line number Diff line
@@ -336,8 +336,9 @@ 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 */

	__u32 old_map_fd;  /* expected old map FD */

};

#define bpf_link_update_opts__last_field old_prog_fd

#define bpf_link_update_opts__last_field old_map_fd



LIBBPF_API int bpf_link_update(int link_fd, int new_prog_fd,

			       const struct bpf_link_update_opts *opts);

tools/lib/bpf/libbpf.c

+35 −0
Original line number Diff line number Diff line
@@ -11677,6 +11677,41 @@ struct bpf_link *bpf_map__attach_struct_ops(const struct bpf_map *map) 
	return &link->link;

}



/*

 * Swap the back struct_ops of a link with a new struct_ops map.

 */

int bpf_link__update_map(struct bpf_link *link, const struct bpf_map *map)

{

	struct bpf_link_struct_ops *st_ops_link;

	__u32 zero = 0;

	int err;



	if (!bpf_map__is_struct_ops(map) || map->fd < 0)

		return -EINVAL;



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

	/* Ensure the type of a link is correct */

	if (st_ops_link->map_fd < 0)

		return -EINVAL;



	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 && err != -EBUSY)

		return err;



	err = bpf_link_update(link->fd, map->fd, NULL);

	if (err < 0)

		return err;



	st_ops_link->map_fd = map->fd;



	return 0;

}



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

							  void *private_data);

tools/lib/bpf/libbpf.h

+1 −0
Original line number Diff line number Diff line
@@ -719,6 +719,7 @@ bpf_program__attach_freplace(const struct bpf_program *prog, 
struct bpf_map;



LIBBPF_API struct bpf_link *bpf_map__attach_struct_ops(const struct bpf_map *map);

LIBBPF_API int bpf_link__update_map(struct bpf_link *link, const struct bpf_map *map);



struct bpf_iter_attach_opts {

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

tools/lib/bpf/libbpf.map

+1 −0
Original line number Diff line number Diff line
@@ -386,6 +386,7 @@ LIBBPF_1.1.0 { 
LIBBPF_1.2.0 {

	global:

		bpf_btf_get_info_by_fd;

		bpf_link__update_map;

		bpf_link_get_info_by_fd;

		bpf_map_get_info_by_fd;

		bpf_prog_get_info_by_fd;