tools: ynl: Add C array attribute decoding to ynl

Add support for decoding C arrays from binay blobs in genetlink-legacy
messages.
Signed-off-by: Donald Hunter <donald.hunter@gmail.com>
Reviewed-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

tools/net/ynl/lib/nlspec.py

@@ -149,8 +149,10 @@ class SpecAttr(SpecElement):
     Represents a single attribute type within an attr space.
 
     Attributes:
-        value      numerical ID when serialized
-        attr_set   Attribute Set containing this attr
+        value         numerical ID when serialized
+        attr_set      Attribute Set containing this attr
+        is_multi      bool, attr may repeat multiple times
+        sub_type      string, name of sub type
     """
     def __init__(self, family, attr_set, yaml, value):
         super().__init__(family, yaml)
@@ -158,6 +160,7 @@ class SpecAttr(SpecElement):
         self.value = value
         self.attr_set = attr_set
         self.is_multi = yaml.get('multi-attr', False)
+        self.sub_type = yaml.get('sub-type')
 
 
 class SpecAttrSet(SpecElement):

tools/net/ynl/lib/ynl.py

@@ -68,6 +68,11 @@ class Netlink:
 
 
 class NlAttr:
+    type_formats = { 'u8' : ('B', 1), 's8' : ('b', 1),
+                     'u16': ('H', 2), 's16': ('h', 2),
+                     'u32': ('I', 4), 's32': ('i', 4),
+                     'u64': ('Q', 8), 's64': ('q', 8) }
+
     def __init__(self, raw, offset):
         self._len, self._type = struct.unpack("HH", raw[offset:offset + 4])
         self.type = self._type & ~Netlink.NLA_TYPE_MASK
@@ -93,6 +98,10 @@ class NlAttr:
     def as_bin(self):
         return self.raw
 
+    def as_c_array(self, type):
+        format, _ = self.type_formats[type]
+        return list({ x[0] for x in struct.iter_unpack(format, self.raw) })
+
     def __repr__(self):
         return f"[type:{self.type} len:{self._len}] {self.raw}"
 
@@ -367,6 +376,13 @@ class YnlFamily(SpecFamily):
             value = enum.entries_by_val[raw - i].name
         rsp[attr_spec['name']] = value
 
+    def _decode_binary(self, attr, attr_spec):
+        if attr_spec.sub_type:
+            decoded = attr.as_c_array(attr_spec.sub_type)
+        else:
+            decoded = attr.as_bin()
+        return decoded
+
     def _decode(self, attrs, space):
         attr_space = self.attr_sets[space]
         rsp = dict()
@@ -386,7 +402,7 @@ class YnlFamily(SpecFamily):
             elif attr_spec["type"] == 'string':
                 decoded = attr.as_strz()
             elif attr_spec["type"] == 'binary':
-                decoded = attr.as_bin()
+                decoded = self._decode_binary(attr, attr_spec)
             elif attr_spec["type"] == 'flag':
                 decoded = True
             else: