tools/net/ynl: Support sub-messages in nested attribute spaces

Sub-message selectors could only be resolved using values from the
current nest level. Enable value lookup in outer scopes by using
collections.ChainMap to implement an ordered lookup from nested to
outer scopes.
Signed-off-by: Donald Hunter <donald.hunter@gmail.com>
Reviewed-by: Jiri Pirko <jiri@nvidia.com>
Link: https://lore.kernel.org/r/20240129223458.52046-3-donald.hunter@gmail.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>

tools/net/ynl/lib/ynl.py

@@ -405,6 +405,26 @@ class GenlProtocol(NetlinkProtocol):
         return self.genl_family['mcast'][mcast_name]
 
 
+
+class SpaceAttrs:
+    SpecValuesPair = namedtuple('SpecValuesPair', ['spec', 'values'])
+
+    def __init__(self, attr_space, attrs, outer = None):
+        outer_scopes = outer.scopes if outer else []
+        inner_scope = self.SpecValuesPair(attr_space, attrs)
+        self.scopes = [inner_scope] + outer_scopes
+
+    def lookup(self, name):
+        for scope in self.scopes:
+            if name in scope.spec:
+                if name in scope.values:
+                    return scope.values[name]
+                spec_name = scope.spec.yaml['name']
+                raise Exception(
+                    f"No value for '{name}' in attribute space '{spec_name}'")
+        raise Exception(f"Attribute '{name}' not defined in any attribute-set")
+
+
 #
 # YNL implementation details.
 #
@@ -548,24 +568,22 @@ class YnlFamily(SpecFamily):
         else:
             rsp[name] = [decoded]
 
-    def _resolve_selector(self, attr_spec, vals):
+    def _resolve_selector(self, attr_spec, search_attrs):
         sub_msg = attr_spec.sub_message
         if sub_msg not in self.sub_msgs:
             raise Exception(f"No sub-message spec named {sub_msg} for {attr_spec.name}")
         sub_msg_spec = self.sub_msgs[sub_msg]
 
         selector = attr_spec.selector
-        if selector not in vals:
-            raise Exception(f"There is no value for {selector} to resolve '{attr_spec.name}'")
-        value = vals[selector]
+        value = search_attrs.lookup(selector)
         if value not in sub_msg_spec.formats:
             raise Exception(f"No message format for '{value}' in sub-message spec '{sub_msg}'")
 
         spec = sub_msg_spec.formats[value]
         return spec
 
-    def _decode_sub_msg(self, attr, attr_spec, rsp):
-        msg_format = self._resolve_selector(attr_spec, rsp)
+    def _decode_sub_msg(self, attr, attr_spec, search_attrs):
+        msg_format = self._resolve_selector(attr_spec, search_attrs)
         decoded = {}
         offset = 0
         if msg_format.fixed_header:
@@ -579,10 +597,12 @@ class YnlFamily(SpecFamily):
                 raise Exception(f"Unknown attribute-set '{attr_space}' when decoding '{attr_spec.name}'")
         return decoded
 
-    def _decode(self, attrs, space):
+    def _decode(self, attrs, space, outer_attrs = None):
         if space:
             attr_space = self.attr_sets[space]
         rsp = dict()
+        search_attrs = SpaceAttrs(attr_space, rsp, outer_attrs)
+
         for attr in attrs:
             try:
                 attr_spec = attr_space.attrs_by_val[attr.type]
@@ -594,7 +614,7 @@ class YnlFamily(SpecFamily):
                 continue
 
             if attr_spec["type"] == 'nest':
-                subdict = self._decode(NlAttrs(attr.raw), attr_spec['nested-attributes'])
+                subdict = self._decode(NlAttrs(attr.raw), attr_spec['nested-attributes'], search_attrs)
                 decoded = subdict
             elif attr_spec["type"] == 'string':
                 decoded = attr.as_strz()
@@ -617,7 +637,7 @@ class YnlFamily(SpecFamily):
                     selector = self._decode_enum(selector, attr_spec)
                 decoded = {"value": value, "selector": selector}
             elif attr_spec["type"] == 'sub-message':
-                decoded = self._decode_sub_msg(attr, attr_spec, rsp)
+                decoded = self._decode_sub_msg(attr, attr_spec, vals)
             else:
                 if not self.process_unknown:
                     raise Exception(f'Unknown {attr_spec["type"]} with name {attr_spec["name"]}')