diff --git a/Documentation/userspace-api/netlink/genetlink-legacy.rst b/Documentation/userspace-api/netlink/genetlink-legacy.rst
index 3bf0bcdf21d8..b8fdcf7f6615 100644
--- a/Documentation/userspace-api/netlink/genetlink-legacy.rst
+++ b/Documentation/userspace-api/netlink/genetlink-legacy.rst

@@ -162,9 +162,77 @@ Other quirks (todo)
 Structures
 ----------
 
-Legacy families can define C structures both to be used as the contents
-of an attribute and as a fixed message header. The plan is to define
-the structs in ``definitions`` and link the appropriate attrs.
+Legacy families can define C structures both to be used as the contents of
+an attribute and as a fixed message header. Structures are defined in
+``definitions``  and referenced in operations or attributes. Note that
+structures defined in YAML are implicitly packed according to C
+conventions. For example, the following struct is 4 bytes, not 6 bytes:
+
+.. code-block:: c
+
+  struct {
+          u8 a;
+          u16 b;
+          u8 c;
+  }
+
+Any padding must be explicitly added and C-like languages should infer the
+need for explicit padding from whether the members are naturally aligned.
+
+Here is the struct definition from above, declared in YAML:
+
+.. code-block:: yaml
+
+  definitions:
+    -
+      name: message-header
+      type: struct
+      members:
+        -
+          name: a
+          type: u8
+        -
+          name: b
+          type: u16
+        -
+          name: c
+          type: u8
+