tools: ynl: Support enums in struct members in genetlink-legacy

Support decoding scalars as enums in struct members for genetlink-legacy
specs.
Signed-off-by: Donald Hunter <donald.hunter@gmail.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Documentation/netlink/genetlink-legacy.yaml

@@ -127,6 +127,9 @@ properties:
               doc:
                 description: Documentation for the struct member attribute.
                 type: string
+              enum:
+                description: Name of the enum type used for the attribute.
+                type: string
         # End genetlink-legacy
 
   attribute-sets:

tools/net/ynl/lib/nlspec.py

@@ -228,11 +228,13 @@ class SpecStructMember(SpecElement):
     Attributes:
         type        string, type of the member attribute
         byte_order  string or None for native byte order
+        enum        string, name of the enum definition
     """
     def __init__(self, family, yaml):
         super().__init__(family, yaml)
         self.type = yaml['type']
         self.byte_order = yaml.get('byte-order')
+        self.enum = yaml.get('enum')
 
 
 class SpecStruct(SpecElement):

tools/net/ynl/lib/ynl.py

@@ -412,7 +412,11 @@ class YnlFamily(SpecFamily):
 
     def _decode_binary(self, attr, attr_spec):
         if attr_spec.struct_name:
-            decoded = attr.as_struct(self.consts[attr_spec.struct_name])
+            members = self.consts[attr_spec.struct_name]
+            decoded = attr.as_struct(members)
+            for m in members:
+                if m.enum:
+                    self._decode_enum(decoded, m)
         elif attr_spec.sub_type:
             decoded = attr.as_c_array(attr_spec.sub_type)
         else: