tools/net/ynl: Add support for nested structs

Make it possible for struct definitions to reference other struct
definitions ofr binary members. For example, the tbf qdisc uses this
struct definition for its parms attribute:

  -
    name: tc-tbf-qopt
    type: struct
    members:
      -
        name: rate
        type: binary
        struct: tc-ratespec
      -
        name: peakrate
        type: binary
        struct: tc-ratespec
      -
        name: limit
        type: u32
      -
        name: buffer
        type: u32
      -
        name: mtu
        type: u32

This adds the necessary schema changes and adds nested struct encoding
and decoding to ynl.

Signed-off-by: Donald Hunter <donald.hunter@gmail.com>
Reviewed-by: Jiri Pirko <jiri@nvidia.com>
Link: https://lore.kernel.org/r/20240129223458.52046-11-donald.hunter@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Documentation/netlink/netlink-raw.yaml

@@ -152,14 +152,23 @@ properties:
                   the right formatting mechanism when displaying values of this
                   type.
                 enum: [ hex, mac, fddi, ipv4, ipv6, uuid ]
+              struct:
+                description: Name of the nested struct type.
+                type: string
             if:
               properties:
                 type:
-                  oneOf:
+                  const: pad
-                    - const: binary
-                    - const: pad
             then:
               required: [ len ]
+            if:
+              properties:
+                type:
+                  const: binary
+            then:
+              oneOf:
+                - required: [ len ]
+                - required: [ struct ]
         # End genetlink-legacy
 
   attribute-sets:

tools/net/ynl/lib/nlspec.py

@@ -248,6 +248,7 @@ class SpecStructMember(SpecElement):
         len         integer, optional byte length of binary types
         display_hint  string, hint to help choose format specifier
                       when displaying the value
+        struct      string, name of nested struct type
     """
     def __init__(self, family, yaml):
         super().__init__(family, yaml)
@@ -256,6 +257,7 @@ class SpecStructMember(SpecElement):
         self.enum = yaml.get('enum')
         self.len = yaml.get('len')
         self.display_hint = yaml.get('display-hint')
+        self.struct = yaml.get('struct')
 
 
 class SpecStruct(SpecElement):

tools/net/ynl/lib/ynl.py

@@ -674,7 +674,10 @@ class YnlFamily(SpecFamily):
             size = 0
             for m in members:
                 if m.type in ['pad', 'binary']:
-                    size += m.len
+                    if m.struct:
+                        size += self._struct_size(m.struct)
+                    else:
+                        size += m.len
                 else:
                     format = NlAttr.get_format(m.type, m.byte_order)
                     size += format.size
@@ -691,8 +694,14 @@ class YnlFamily(SpecFamily):
             if m.type == 'pad':
                 offset += m.len
             elif m.type == 'binary':
-                value = data[offset : offset + m.len]
+                if m.struct:
-                offset += m.len
+                    len = self._struct_size(m.struct)
+                    value = self._decode_struct(data[offset : offset + len],
+                                                m.struct)
+                    offset += len
+                else:
+                    value = data[offset : offset + m.len]
+                    offset += m.len
             else:
                 format = NlAttr.get_format(m.type, m.byte_order)
                 [ value ] = format.unpack_from(data, offset)
@@ -713,10 +722,15 @@ class YnlFamily(SpecFamily):
             if m.type == 'pad':
                 attr_payload += bytearray(m.len)
             elif m.type == 'binary':
-                if value is None:
+                if m.struct:
-                    attr_payload += bytearray(m.len)
+                    if value is None:
+                        value = dict()
+                    attr_payload += self._encode_struct(m.struct, value)
                 else:
-                    attr_payload += bytes.fromhex(value)
+                    if value is None:
+                        attr_payload += bytearray(m.len)
+                    else:
+                        attr_payload += bytes.fromhex(value)
             else:
                 if value is None:
                     value = 0