tools: ynl: add scope qualifier for definitions

Using definitions in kernel policies is awkward right now.
On one hand we want defines for max values and such.
On the other we don't have a way of adding kernel-only defines.
Adding unnecessary defines to uAPI is a bad idea, we won't
be able to delete them. And when it comes to policy user
space should just query it via the policy dump, not use
hard coded defines.

Add a "scope" property to definitions, which will let us tell
the codegen that a definition is for kernel use only. Support
following values:
  - uapi: render into the uAPI header (default, today's behavior)
  - kernel: render to kernel header only
  - user: same as kernel but for the user-side generated header

Definitions may have a header property (definition is "external",
provided by existing header). Extend the scope to headers, too.
If definition has both scope and header properties we will only
generate the includes in the right scope.

Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Link: https://patch.msgid.link/20260510192904.3987113-8-kuba@kernel.org
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

Documentation/netlink/genetlink-c.yaml

@@ -69,6 +69,15 @@ properties:
         header:
           description: For C-compatible languages, header which already defines this value.
           type: string
+        scope:
+          description: |
+            Visibility of this definition. "uapi" (default) renders into
+            the uAPI header, "kernel" renders into the kernel-side
+            generated header, "user" renders into the user-side
+            generated header. When combined with `header:`, the
+            definition is not rendered, and the named header is
+            included only by code matching the scope.
+          enum: [ uapi, kernel, user ]
         type:
           enum: [ const, enum, flags ]
         doc:

Documentation/netlink/genetlink-legacy.yaml

@@ -83,6 +83,15 @@ properties:
         header:
           description: For C-compatible languages, header which already defines this value.
           type: string
+        scope:
+          description: |
+            Visibility of this definition. "uapi" (default) renders into
+            the uAPI header, "kernel" renders into the kernel-side
+            generated header, "user" renders into the user-side
+            generated header. When combined with `header:`, the
+            definition is not rendered, and the named header is
+            included only by code matching the scope.
+          enum: [ uapi, kernel, user ]
         type:
           enum: [ const, enum, flags, struct ] # Trim
         doc:

Documentation/netlink/genetlink.yaml

@@ -55,6 +55,15 @@ properties:
         header:
           description: For C-compatible languages, header which already defines this value.
           type: string
+        scope:
+          description: |
+            Visibility of this definition. "uapi" (default) renders into
+            the uAPI header, "kernel" renders into the kernel-side
+            generated header, "user" renders into the user-side
+            generated header. When combined with `header:`, the
+            definition is not rendered, and the named header is
+            included only by code matching the scope.
+          enum: [ uapi, kernel, user ]
         type:
           enum: [ const, enum, flags ]
         doc:

Documentation/netlink/netlink-raw.yaml

@@ -87,6 +87,15 @@ properties:
         header:
           description: For C-compatible languages, header which already defines this value.
           type: string
+        scope:
+          description: |
+            Visibility of this definition. "uapi" (default) renders into
+            the uAPI header, "kernel" renders into the kernel-side
+            generated header, "user" renders into the user-side
+            generated header. When combined with `header:`, the
+            definition is not rendered, and the named header is
+            included only by code matching the scope.
+          enum: [ uapi, kernel, user ]
         type:
           enum: [ const, enum, flags, struct ] # Trim
         doc:

tools/net/ynl/pyynl/ynl_gen_c.py

@@ -3212,6 +3212,8 @@ def render_uapi(family, cw):
     for const in family['definitions']:
         if const.get('header'):
             continue
+        if const.get('scope', 'uapi') != 'uapi':
+            continue
 
         if const['type'] != 'const':
             cw.writes_defines(defines)
@@ -3339,6 +3341,25 @@ def render_uapi(family, cw):
     cw.p(f'#endif /* {hdr_prot} */')
 
 
+def render_scoped_consts(family, cw, scope):
+    defines = []
+    for const in family['definitions']:
+        if const['type'] != 'const':
+            continue
+        if const.get('header'):
+            continue
+        if const.get('scope') != scope:
+            continue
+        name_pfx = const.get('name-prefix', f"{family.ident_name}-")
+        defines.append([
+            c_upper(family.get('c-define-name',
+                               f"{name_pfx}{const['name']}")),
+            const['value']])
+    if defines:
+        cw.writes_defines(defines)
+        cw.nl()
+
+
 def _render_user_ntf_entry(ri, op):
     if not ri.family.is_classic():
         ri.cw.block_start(line=f"[{op.enum_name}] = ")
@@ -3504,8 +3525,12 @@ def main():
             cw.p('#include "ynl.h"')
         headers = []
     for definition in parsed['definitions'] + parsed['attribute-sets']:
-        if 'header' in definition:
-            headers.append(definition['header'])
+        if 'header' not in definition:
+            continue
+        scope = definition.get('scope', 'uapi')
+        if scope != 'uapi' and scope != args.mode:
+            continue
+        headers.append(definition['header'])
     if args.mode == 'user':
         headers.append(parsed.uapi_header)
     seen_header = []
@@ -3522,6 +3547,7 @@ def main():
             for one in args.user_header:
                 cw.p(f'#include "{one}"')
         else:
+            render_scoped_consts(parsed, cw, 'user')
             cw.p('struct ynl_sock;')
             cw.nl()
             render_user_family(parsed, cw, True)
@@ -3529,6 +3555,7 @@ def main():
 
     if args.mode == "kernel":
         if args.header:
+            render_scoped_consts(parsed, cw, 'kernel')
             for _, struct in sorted(parsed.pure_nested_structs.items()):
                 if struct.request:
                     cw.p('/* Common nested types */')