tools: ynl: use 1 as the default for first entry in attrs/ops

Pretty much all families use value: 1 or reserve as unspec
the first entry in attribute set and the first operation.
Make this the default. Update documentation (the doc for
values of operations just refers back to doc for attrs
so updating only attrs).
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

Documentation/userspace-api/netlink/specs.rst

@@ -197,7 +197,12 @@ value
 Numerical attribute ID, used in serialized Netlink messages.
 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.
+and ``1`` for the first attribute in the attribute set.
+
+Attributes (and operations) use ``1`` as the default value for the first
+entry (unlike enums in definitions which start from ``0``) because
+entry ``0`` is almost always reserved as undefined. Spec can explicitly
+set value to ``0`` if needed.
 
 Note that the ``value`` of an attribute is defined only in its main set
 (not in subsets).

tools/net/ynl/lib/nlspec.py

@@ -96,7 +96,7 @@ class SpecAttrSet(SpecElement):
         self.attrs_by_val = collections.OrderedDict()
 
         if self.subset_of is None:
-            val = 0
+            val = 1
             for elem in self.yaml['attributes']:
                 if 'value' in elem:
                     val = elem['value']
@@ -252,7 +252,7 @@ class SpecFamily(SpecElement):
         self._resolution_list.append(elem)
 
     def _dictify_ops_unified(self):
-        val = 0
+        val = 1
         for elem in self.yaml['operations']['list']:
             if 'value' in elem:
                 val = elem['value']
@@ -263,7 +263,7 @@ class SpecFamily(SpecElement):
             self.msgs[op.name] = op
 
     def _dictify_ops_directional(self):
-        req_val = rsp_val = 0
+        req_val = rsp_val = 1
         for elem in self.yaml['operations']['list']:
             if 'notify' in elem:
                 if 'value' in elem:

tools/net/ynl/ynl-gen-c.py

@@ -2044,14 +2044,17 @@ def render_uapi(family, cw):
     max_value = f"({cnt_name} - 1)"
 
     uapi_enum_start(family, cw, family['operations'], 'enum-name')
+    val = 0
     for op in family.msgs.values():
         if separate_ntf and ('notify' in op or 'event' in op):
             continue
 
         suffix = ','
-        if 'value' in op:
-            suffix = f" = {op['value']},"
+        if op.value != val:
+            suffix = f" = {op.value},"
+            val = op.value
         cw.p(op.enum_name + suffix)
+        val += 1
     cw.nl()
     cw.p(cnt_name + ('' if max_by_define else ','))
     if not max_by_define: