Re: [PATCH bpf-next v13 07/14] bpf: pass attached BTF to the bpf_struct_ops subsystem

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On 12/14/23 18:44, Martin KaFai Lau wrote:
On 12/8/23 4:27 PM, thinker.li@xxxxxxxxx wrote:
@@ -681,15 +682,30 @@ static struct bpf_map *bpf_struct_ops_map_alloc(union bpf_attr *attr)
      struct bpf_struct_ops_map *st_map;
      const struct btf_type *t, *vt;
      struct bpf_map *map;
+    struct btf *btf;
      int ret;
-    st_ops_desc = bpf_struct_ops_find_value(btf_vmlinux, attr->btf_vmlinux_value_type_id);
-    if (!st_ops_desc)
-        return ERR_PTR(-ENOTSUPP);
+    if (attr->value_type_btf_obj_fd) {
+        /* The map holds btf for its whole life time. */
+        btf = btf_get_by_fd(attr->value_type_btf_obj_fd);
+        if (IS_ERR(btf))
+            return ERR_PTR(PTR_ERR(btf));

             return ERR_CAST(btf);

It needs to check for btf_is_module:

         if (!btf_is_module(btf)) {
             btf_put(btf);
             return ERR_PTR(-EINVAL);
         }

Even btf is btf_vmlinux the kernel's btf, it still works.
Although libbpf pass 0 as the value of value_type_btf_obj_fd for
btf_vmlinux now, it should be OK for a user space loader to
pass a fd of btf_vmlinux.

WDYT?


+    } else {
+        btf = btf_vmlinux;
+        btf_get(btf);

btf_vmlinux could be NULL or a ERR_PTR? Lets take this chance to use bpf_get_btf_vmlinux():
         btf = bpf_get_btf_vmlinux();
             if (IS_ERR(btf))
                     return ERR_CAST(btf);

Sure!


Going back to patch 4. This should be the only case that btf will be NULL or ERR_PTR?

will continue the remaining review later tonight.

pw-bot: cr

+    }
+
+    st_ops_desc = bpf_struct_ops_find_value(btf, attr->btf_vmlinux_value_type_id);
+    if (!st_ops_desc) {
+        ret = -ENOTSUPP;
+        goto errout;
+    }
      vt = st_ops_desc->value_type;
-    if (attr->value_size != vt->size)
-        return ERR_PTR(-EINVAL);
+    if (attr->value_size != vt->size) {
+        ret = -EINVAL;
+        goto errout;
+    }
      t = st_ops_desc->type;





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