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

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On 3/21/23 10:49, Martin KaFai Lau wrote:
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.

Ouch! Will fixed it.


[ 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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