Re: [PATCH bpf-next v9 4/8] libbpf: Create a bpf_link in bpf_map__attach_struct_ops().

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On 3/20/23 12:56 PM, Kui-Feng Lee wrote:
  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);
@@ -11596,31 +11637,32 @@ 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 != -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)) {

hmm... This still does not look right. 'err' could be -EBUSY here and should not be treated as success for non BPF_F_LINK case. The above 'err && err != -EBUSY' check should also consider the BPF_F_LINK map_flags.

[ Replied on the wrong v9, so copy-and-paste the reply back to this v9. ]

+		/* 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,




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