Re: [PATCH bpf-next v5 4/8] libbpf: Create a bpf_link in bpf_map__attach_struct_ops().

Martin KaFai Lau
2023-03-08T21:44:08Z

On 3/7/23 4:50 PM, Kui-Feng Lee wrote:
> @@ -11566,22 +11591,34 @@ 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) {

map_fd < 0 should always be true?

> + /* Fake bpf_link */
> + if (bpf_map_delete_elem(link->fd, &zero))
> + return -errno;
> + return 0;
> + }
> +
> + /* Doesn't support detaching. */
> + return -EOPNOTSUPP;
> }
>
> 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);
> @@ -11590,31 +11627,34 @@ 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);
> + if (err) {
> + err = -errno;
> + free(link);
> + return libbpf_err_ptr(err);
> + }
>
> - 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;
> + if (!(map->def.map_flags & BPF_F_LINK)) {
> + /* Fake bpf_link */
> + link->link.fd = map->fd;
> + link->map_fd = -1;
> + link->link.detach = bpf_link__detach_struct_ops;
> + return &link->link;
> }
>
> - err = bpf_map_update_elem(map->fd, &zero, st_ops->kern_vdata, 0);
> - if (err) {
> + fd = bpf_link_create(map->fd, -1, BPF_STRUCT_OPS, NULL);
> + if (fd < 0) {
> err = -errno;
> free(link);
> return libbpf_err_ptr(err);
> }
>
> - link->detach = bpf_link__detach_struct_ops;
> - link->fd = map->fd;
> + link->link.fd = fd;
> + link->map_fd = map->fd;

Does it need to set link->link.detach?

>
> - return link;
> + return &link->link;
> }
>
> typedef enum bpf_perf_event_ret (*bpf_perf_event_print_t)(struct perf_event_header *hdr,