tools: ynl: correctly handle overrides of fields in subset

We stated in documentation [1] and previous discussions [2]
that the need for overriding fields in members of subsets
is anticipated. Implement it.

Since each attr is now a new object we need to make sure
that the modifications are propagated. Specifically C codegen
wants to annotate which attrs are used in requests and replies
to generate the right validation artifacts.

[1] https://docs.kernel.org/next/userspace-api/netlink/specs.html#subset-of
[2] https://lore.kernel.org/netdev/20231004171350.1f59cd1d@kernel.org/

Reviewed-by: Donald Hunter <donald.hunter@gmail.com>
Link: https://patch.msgid.link/20250107022820.2087101-2-kuba@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

tools/net/ynl/lib/nlspec.py

@@ -219,7 +219,10 @@ class SpecAttrSet(SpecElement):
         else:
             real_set = family.attr_sets[self.subset_of]
             for elem in self.yaml['attributes']:
-                attr = real_set[elem['name']]
+                real_attr = real_set[elem['name']]
+                combined_elem = real_attr.yaml | elem
+                attr = self.new_attr(combined_elem, real_attr.value)
+
                 self.attrs[attr.name] = attr
                 self.attrs_by_val[attr.value] = attr
 

tools/net/ynl/ynl-gen-c.py

@@ -79,6 +79,20 @@ class Type(SpecAttr):
         self.enum_name = None
         delattr(self, "enum_name")
 
+    def _get_real_attr(self):
+        # if the attr is for a subset return the "real" attr (just one down, does not recurse)
+        return self.family.attr_sets[self.attr_set.subset_of][self.name]
+
+    def set_request(self):
+        self.request = True
+        if self.attr_set.subset_of:
+            self._get_real_attr().set_request()
+
+    def set_reply(self):
+        self.reply = True
+        if self.attr_set.subset_of:
+            self._get_real_attr().set_reply()
+
     def get_limit(self, limit, default=None):
         value = self.checks.get(limit, default)
         if value is None:
@@ -106,6 +120,10 @@ class Type(SpecAttr):
             enum_name = f"{self.attr_set.name_prefix}{self.name}"
         self.enum_name = c_upper(enum_name)
 
+        if self.attr_set.subset_of:
+            if self.checks != self._get_real_attr().checks:
+                raise Exception("Overriding checks not supported by codegen, yet")
+
     def is_multi_val(self):
         return None
 
@@ -1119,17 +1137,17 @@ class Family(SpecFamily):
         for _, struct in self.pure_nested_structs.items():
             if struct.request:
                 for _, arg in struct.member_list():
-                    arg.request = True
+                    arg.set_request()
             if struct.reply:
                 for _, arg in struct.member_list():
-                    arg.reply = True
+                    arg.set_reply()
 
         for root_set, rs_members in self.root_sets.items():
             for attr, spec in self.attr_sets[root_set].items():
                 if attr in rs_members['request']:
-                    spec.request = True
+                    spec.set_request()
                 if attr in rs_members['reply']:
-                    spec.reply = True
+                    spec.set_reply()
 
     def _load_global_policy(self):
         global_set = set()