tools/net/ynl: Implement nlattr array-nest decoding in ynl

Add support for the 'array-nest' attribute type that is used by several
netlink-raw families.

Signed-off-by: Donald Hunter <donald.hunter@gmail.com>
Reviewed-by: Jakub Kicinski <kuba@kernel.org>
Reviewed-by: Jacob Keller <jacob.e.keller@intel.com>
Link: https://lore.kernel.org/r/20230825122756.7603-9-donald.hunter@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Author: donaldh

tools/net/ynl/lib/ynl.py

@@ -497,6 +497,17 @@ def _decode_binary(self, attr, attr_spec):
                 decoded = NlAttr.formatted_string(decoded, attr_spec.display_hint)
         return decoded
 
+    def _decode_array_nest(self, attr, attr_spec):
+        decoded = []
+        offset = 0
+        while offset < len(attr.raw):
+            item = NlAttr(attr.raw, offset)
+            offset += item.full_len
+
+            subattrs = self._decode(NlAttrs(item.raw), attr_spec['nested-attributes'])
+            decoded.append({ item.type: subattrs })
+        return decoded
+
     def _decode(self, attrs, space):
         attr_space = self.attr_sets[space]
         rsp = dict()
@@ -516,6 +527,8 @@ def _decode(self, attrs, space):
                 decoded = True
             elif attr_spec["type"] in NlAttr.type_formats:
                 decoded = attr.as_scalar(attr_spec['type'], attr_spec.byte_order)
+            elif attr_spec["type"] == 'array-nest':
+                decoded = self._decode_array_nest(attr, attr_spec)
             else:
                 raise Exception(f'Unknown {attr_spec["type"]} with name {attr_spec["name"]}')