tools: ynl-gen: store recursive nests by a pointer

To avoid infinite nesting store recursive structs by pointer.
If recursive struct is placed in the op directly - the first
instance can be stored by value. That makes the code much
less of a pain for majority of practical uses.
Reviewed-by: Donald Hunter <donald.hunter@gmail.com>
Link: https://lore.kernel.org/r/20231213231432.2944749-8-kuba@kernel.orgSigned-off-by: Jakub Kicinski <kuba@kernel.org>

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

@@ -108,6 +108,9 @@ class Type(SpecAttr):
     def is_recursive(self):
         return False
 
+    def is_recursive_for_op(self, ri):
+        return self.is_recursive() and not ri.op
+
     def presence_type(self):
         return 'bit'
 
@@ -148,6 +151,8 @@ class Type(SpecAttr):
         member = self._complex_member_type(ri)
         if member:
             ptr = '*' if self.is_multi_val() else ''
+            if self.is_recursive_for_op(ri):
+                ptr = '*'
             ri.cw.p(f"{member} {ptr}{self.c_name};")
             return
         members = self.arg_member(ri)
@@ -539,7 +544,11 @@ class TypeNest(Type):
         return self.nested_struct_type
 
     def free(self, ri, var, ref):
-        ri.cw.p(f'{self.nested_render_name}_free(&{var}->{ref}{self.c_name});')
+        at = '&'
+        if self.is_recursive_for_op(ri):
+            at = ''
+            ri.cw.p(f'if ({var}->{ref}{self.c_name})')
+        ri.cw.p(f'{self.nested_render_name}_free({at}{var}->{ref}{self.c_name});')
 
     def _attr_typol(self):
         return f'.type = YNL_PT_NEST, .nest = &{self.nested_render_name}_nest, '
@@ -548,8 +557,9 @@ class TypeNest(Type):
         return 'NLA_POLICY_NESTED(' + self.nested_render_name + '_nl_policy)'
 
     def attr_put(self, ri, var):
+        at = '' if self.is_recursive_for_op(ri) else '&'
         self._attr_put_line(ri, var, f"{self.nested_render_name}_put(nlh, " +
-                            f"{self.enum_name}, &{var}->{self.c_name})")
+                            f"{self.enum_name}, {at}{var}->{self.c_name})")
 
     def _attr_get(self, ri, var):
         get_lines = [f"if ({self.nested_render_name}_parse(&parg, attr))",
@@ -562,6 +572,8 @@ class TypeNest(Type):
         ref = (ref if ref else []) + [self.c_name]
 
         for _, attr in ri.family.pure_nested_structs[self.nested_attrs].member_list():
+            if attr.is_recursive():
+                continue
             attr.setter(ri, self.nested_attrs, direction, deref=deref, ref=ref)