tools: ynl: fully inherit attrs in subsets

To avoid having to repeat the entire definition of an attribute
(including the value) use the Attr object from the original set.
In fact this is already the documented expectation.

Fixes: be5bea1c ("net: add basic C code generators for Netlink")
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

Documentation/userspace-api/netlink/specs.rst

@@ -199,7 +199,8 @@ The ``value`` property can be skipped, in which case the attribute ID
 will be the value of the previous attribute plus one (recursively)
 and ``0`` for the first attribute in the attribute set.
 
-Note that the ``value`` of an attribute is defined only in its main set.
+Note that the ``value`` of an attribute is defined only in its main set
+(not in subsets).
 
 enum
 ~~~~

tools/net/ynl/lib/nlspec.py

@@ -95,6 +95,7 @@ class SpecAttrSet(SpecElement):
         self.attrs = collections.OrderedDict()
         self.attrs_by_val = collections.OrderedDict()
 
+        if self.subset_of is None:
             val = 0
             for elem in self.yaml['attributes']:
                 if 'value' in elem:
@@ -104,6 +105,12 @@ class SpecAttrSet(SpecElement):
                 self.attrs[attr.name] = attr
                 self.attrs_by_val[attr.value] = attr
                 val += 1
+        else:
+            real_set = family.attr_sets[self.subset_of]
+            for elem in self.yaml['attributes']:
+                attr = real_set[elem['name']]
+                self.attrs[attr.name] = attr
+                self.attrs_by_val[attr.value] = attr
 
     def new_attr(self, elem, value):
         return SpecAttr(self.family, self, elem, value)