tools: ynl: Use dict of predefined Structs to decode scalar types

Use a dict of predefined Struct() objects to decode scalar types in native,
big or little endian format. This removes the repetitive code for the
scalar variants and ensures all the signed variants are supported.
Signed-off-by: Donald Hunter <donald.hunter@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

tools/net/ynl/lib/ynl.py

 # SPDX-License-Identifier: GPL-2.0 OR BSD-3-Clause
 
+from collections import namedtuple
 import functools
 import os
 import random
 import socket
 import struct
+from struct import Struct
 import yaml
 
 from .nlspec import SpecFamily
@@ -76,10 +78,17 @@ class NlError(Exception):
 
 
 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) }
+    ScalarFormat = namedtuple('ScalarFormat', ['native', 'big', 'little'])
+    type_formats = {
+        'u8' : ScalarFormat(Struct('B'), Struct("B"),  Struct("B")),
+        's8' : ScalarFormat(Struct('b'), Struct("b"),  Struct("b")),
+        'u16': ScalarFormat(Struct('H'), Struct(">H"), Struct("<H")),
+        's16': ScalarFormat(Struct('h'), Struct(">h"), Struct("<h")),
+        'u32': ScalarFormat(Struct('I'), Struct(">I"), Struct("<I")),
+        's32': ScalarFormat(Struct('i'), Struct(">i"), Struct("<i")),
+        'u64': ScalarFormat(Struct('Q'), Struct(">Q"), Struct("<Q")),
+        's64': ScalarFormat(Struct('q'), Struct(">q"), Struct("<q"))
+    }
 
     def __init__(self, raw, offset):
         self._len, self._type = struct.unpack("HH", raw[offset:offset + 4])
@@ -88,25 +97,17 @@ class NlAttr:
         self.full_len = (self.payload_len + 3) & ~3
         self.raw = raw[offset + 4:offset + self.payload_len]
 
-    def format_byte_order(byte_order):
+    @classmethod
+    def get_format(cls, attr_type, byte_order=None):
+        format = cls.type_formats[attr_type]
         if byte_order:
-            return ">" if byte_order == "big-endian" else "<"
-        return ""
+            return format.big if byte_order == "big-endian" \
+                else format.little
+        return format.native
 
-    def as_u8(self):
-        return struct.unpack("B", self.raw)[0]
-
-    def as_u16(self, byte_order=None):
-        endian = NlAttr.format_byte_order(byte_order)
-        return struct.unpack(f"{endian}H", self.raw)[0]
-
-    def as_u32(self, byte_order=None):
-        endian = NlAttr.format_byte_order(byte_order)
-        return struct.unpack(f"{endian}I", self.raw)[0]
-
-    def as_u64(self, byte_order=None):
-        endian = NlAttr.format_byte_order(byte_order)
-        return struct.unpack(f"{endian}Q", self.raw)[0]
+    def as_scalar(self, attr_type, byte_order=None):
+        format = self.get_format(attr_type, byte_order)
+        return format.unpack(self.raw)[0]
 
     def as_strz(self):
         return self.raw.decode('ascii')[:-1]
@@ -115,17 +116,17 @@ class NlAttr:
         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) })
+        format = self.get_format(type)
+        return [ x[0] for x in format.iter_unpack(self.raw) ]
 
     def as_struct(self, members):
         value = dict()
         offset = 0
         for m in members:
             # TODO: handle non-scalar members
-            format, size = self.type_formats[m.type]
-            decoded = struct.unpack_from(format, self.raw, offset)
-            offset += size
+            format = self.get_format(m.type)
+            decoded = format.unpack_from(self.raw, offset)
+            offset += format.size
             value[m.name] = decoded[0]
         return value
 
@@ -184,11 +185,11 @@ class NlMsg:
                 if extack.type == Netlink.NLMSGERR_ATTR_MSG:
                     self.extack['msg'] = extack.as_strz()
                 elif extack.type == Netlink.NLMSGERR_ATTR_MISS_TYPE:
-                    self.extack['miss-type'] = extack.as_u32()
+                    self.extack['miss-type'] = extack.as_scalar('u32')
                 elif extack.type == Netlink.NLMSGERR_ATTR_MISS_NEST:
-                    self.extack['miss-nest'] = extack.as_u32()
+                    self.extack['miss-nest'] = extack.as_scalar('u32')
                 elif extack.type == Netlink.NLMSGERR_ATTR_OFFS:
-                    self.extack['bad-attr-offs'] = extack.as_u32()
+                    self.extack['bad-attr-offs'] = extack.as_scalar('u32')
                 else:
                     if 'unknown' not in self.extack:
                         self.extack['unknown'] = []
@@ -272,11 +273,11 @@ def _genl_load_families():
                 fam = dict()
                 for attr in gm.raw_attrs:
                     if attr.type == Netlink.CTRL_ATTR_FAMILY_ID:
-                        fam['id'] = attr.as_u16()
+                        fam['id'] = attr.as_scalar('u16')
                     elif attr.type == Netlink.CTRL_ATTR_FAMILY_NAME:
                         fam['name'] = attr.as_strz()
                     elif attr.type == Netlink.CTRL_ATTR_MAXATTR:
-                        fam['maxattr'] = attr.as_u32()
+                        fam['maxattr'] = attr.as_scalar('u32')
                     elif attr.type == Netlink.CTRL_ATTR_MCAST_GROUPS:
                         fam['mcast'] = dict()
                         for entry in NlAttrs(attr.raw):
@@ -286,7 +287,7 @@ def _genl_load_families():
                                 if entry_attr.type == Netlink.CTRL_ATTR_MCAST_GRP_NAME:
                                     mcast_name = entry_attr.as_strz()
                                 elif entry_attr.type == Netlink.CTRL_ATTR_MCAST_GRP_ID:
-                                    mcast_id = entry_attr.as_u32()
+                                    mcast_id = entry_attr.as_scalar('u32')
                             if mcast_name and mcast_id is not None:
                                 fam['mcast'][mcast_name] = mcast_id
                 if 'name' in fam and 'id' in fam:
@@ -304,9 +305,9 @@ class GenlMsg:
 
         self.fixed_header_attrs = dict()
         for m in fixed_header_members:
-            format, size = NlAttr.type_formats[m.type]
-            decoded = struct.unpack_from(format, nl_msg.raw, offset)
-            offset += size
+            format = NlAttr.get_format(m.type)
+            decoded = format.unpack_from(nl_msg.raw, offset)
+            offset += format.size
             self.fixed_header_attrs[m.name] = decoded[0]
 
         self.raw = nl_msg.raw[offset:]
@@ -381,21 +382,13 @@ class YnlFamily(SpecFamily):
                 attr_payload += self._add_attr(attr['nested-attributes'], subname, subvalue)
         elif attr["type"] == 'flag':
             attr_payload = b''
-        elif attr["type"] == 'u8':
-            attr_payload = struct.pack("B", int(value))
-        elif attr["type"] == 'u16':
-            endian = NlAttr.format_byte_order(attr.byte_order)
-            attr_payload = struct.pack(f"{endian}H", int(value))
-        elif attr["type"] == 'u32':
-            endian = NlAttr.format_byte_order(attr.byte_order)
-            attr_payload = struct.pack(f"{endian}I", int(value))
-        elif attr["type"] == 'u64':
-            endian = NlAttr.format_byte_order(attr.byte_order)
-            attr_payload = struct.pack(f"{endian}Q", int(value))
         elif attr["type"] == 'string':
             attr_payload = str(value).encode('ascii') + b'\x00'
         elif attr["type"] == 'binary':
             attr_payload = value
+        elif attr['type'] in NlAttr.type_formats:
+            format = NlAttr.get_format(attr['type'], attr.byte_order)
+            attr_payload = format.pack(int(value))
         else:
             raise Exception(f'Unknown type at {space} {name} {value} {attr["type"]}')
 
@@ -434,22 +427,16 @@ class YnlFamily(SpecFamily):
             if attr_spec["type"] == 'nest':
                 subdict = self._decode(NlAttrs(attr.raw), attr_spec['nested-attributes'])
                 decoded = subdict
-            elif attr_spec['type'] == 'u8':
-                decoded = attr.as_u8()
-            elif attr_spec['type'] == 'u16':
-                decoded = attr.as_u16(attr_spec.byte_order)
-            elif attr_spec['type'] == 'u32':
-                decoded = attr.as_u32(attr_spec.byte_order)
-            elif attr_spec['type'] == 'u64':
-                decoded = attr.as_u64(attr_spec.byte_order)
             elif attr_spec["type"] == 'string':
                 decoded = attr.as_strz()
             elif attr_spec["type"] == 'binary':
                 decoded = self._decode_binary(attr, attr_spec)
             elif attr_spec["type"] == 'flag':
                 decoded = True
+            elif attr_spec["type"] in NlAttr.type_formats:
+                decoded = attr.as_scalar(attr_spec['type'], attr_spec.byte_order)
             else:
-                raise Exception(f'Unknown {attr.type} {attr_spec["name"]} {attr_spec["type"]}')
+                raise Exception(f'Unknown {attr_spec["type"]} with name {attr_spec["name"]}')
 
             if not attr_spec.is_multi:
                 rsp[attr_spec['name']] = decoded
@@ -555,8 +542,8 @@ class YnlFamily(SpecFamily):
             fixed_header_members = self.consts[op.fixed_header].members
             for m in fixed_header_members:
                 value = vals.pop(m.name)
-                format, _ = NlAttr.type_formats[m.type]
-                msg += struct.pack(format, value)
+                format = NlAttr.get_format(m.type)
+                msg += format.pack(value)
         for name, value in vals.items():
             msg += self._add_attr(op.attr_set.name, name, value)
         msg = _genl_msg_finalize(msg)