netlink: specs: support generating code for genl socket priv

The family struct is auto-generated for new families, support
use of the sock_priv_* mechanism added in commit a731132
("genetlink: introduce per-sock family private storage").

For example if the family wants to use struct sk_buff as its
private struct (unrealistic but just for illustration), it would
add to its spec:

  kernel-family:
    headers: [ "linux/skbuff.h" ]
    sock-priv: struct sk_buff

ynl-gen-c will declare the appropriate priv size and hook
in function prototypes to be implemented by the family.

Link: https://lore.kernel.org/r/20240308190319.2523704-1-kuba@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Author: kuba-moo

Documentation/netlink/genetlink-c.yaml

@@ -378,3 +378,22 @@ properties:
               type: string
             # End genetlink-c
             flags: *cmd_flags
+
+  kernel-family:
+    description: Additional global attributes used for kernel C code generation.
+    type: object
+    additionalProperties: False
+    properties:
+      headers:
+        description: |
+          List of extra headers which should be included in the source
+          of the generated code.
+        type: array
+        items:
+          type: string
+      sock-priv:
+        description: |
+          Literal name of the type which is used within the kernel
+          to store the socket state. The type / structure is internal
+          to the kernel, and is not defined in the spec.
+        type: string

Documentation/netlink/genetlink-legacy.yaml

@@ -439,3 +439,22 @@ properties:
               type: string
             # End genetlink-c
             flags: *cmd_flags
+
+  kernel-family:
+    description: Additional global attributes used for kernel C code generation.
+    type: object
+    additionalProperties: False
+    properties:
+      headers:
+        description: |
+          List of extra headers which should be included in the source
+          of the generated code.
+        type: array
+        items:
+          type: string
+      sock-priv:
+        description: |
+          Literal name of the type which is used within the kernel
+          to store the socket state. The type / structure is internal
+          to the kernel, and is not defined in the spec.
+        type: string

Documentation/netlink/genetlink.yaml

@@ -328,3 +328,22 @@ properties:
                 The name for the group, used to form the define and the value of the define.
               type: string
             flags: *cmd_flags
+
+  kernel-family:
+    description: Additional global attributes used for kernel C code generation.
+    type: object
+    additionalProperties: False
+    properties:
+      headers:
+        description: |
+          List of extra headers which should be included in the source
+          of the generated code.
+        type: array
+        items:
+          type: string
+      sock-priv:
+        description: |
+          Literal name of the type which is used within the kernel
+          to store the socket state. The type / structure is internal
+          to the kernel, and is not defined in the spec.
+        type: string

tools/net/ynl/lib/nlspec.py

@@ -418,6 +418,7 @@ class SpecFamily(SpecElement):
         consts     dict of all constants/enums
         fixed_header  string, optional name of family default fixed header struct
         mcast_groups  dict of all multicast groups (index by name)
+        kernel_family   dict of kernel family attributes
     """
     def __init__(self, spec_path, schema_path=None, exclude_ops=None):
         with open(spec_path, "r") as stream:
@@ -461,6 +462,7 @@ def __init__(self, spec_path, schema_path=None, exclude_ops=None):
         self.ntfs = collections.OrderedDict()
         self.consts = collections.OrderedDict()
         self.mcast_groups = collections.OrderedDict()
+        self.kernel_family = collections.OrderedDict(self.yaml.get('kernel-family', {}))
 
         last_exception = None
         while len(self._resolution_list) > 0:

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

@@ -2342,6 +2342,10 @@ def print_kernel_family_struct_hdr(family, cw):
 
     cw.p(f"extern struct genl_family {family.c_name}_nl_family;")
     cw.nl()
+    if 'sock-priv' in family.kernel_family:
+        cw.p(f'void {family.c_name}_nl_sock_priv_init({family.kernel_family["sock-priv"]} *priv);')
+        cw.p(f'void {family.c_name}_nl_sock_priv_destroy({family.kernel_family["sock-priv"]} *priv);')
+        cw.nl()
 
 
 def print_kernel_family_struct_src(family, cw):
@@ -2363,6 +2367,11 @@ def print_kernel_family_struct_src(family, cw):
     if family.mcgrps['list']:
         cw.p(f'.mcgrps\t\t= {family.c_name}_nl_mcgrps,')
         cw.p(f'.n_mcgrps\t= ARRAY_SIZE({family.c_name}_nl_mcgrps),')
+    if 'sock-priv' in family.kernel_family:
+        cw.p(f'.sock_priv_size\t= sizeof({family.kernel_family["sock-priv"]}),')
+        # Force cast here, actual helpers take pointer to the real type.
+        cw.p(f'.sock_priv_init\t= (void *){family.c_name}_nl_sock_priv_init,')
+        cw.p(f'.sock_priv_destroy = (void *){family.c_name}_nl_sock_priv_destroy,')
     cw.block_end(';')
 
 
@@ -2659,6 +2668,7 @@ def main():
                 cw.p(f'#include "{os.path.basename(args.out_file[:-2])}.h"')
             cw.nl()
         headers = ['uapi/' + parsed.uapi_header]
+        headers += parsed.kernel_family.get('headers', [])
     else:
         cw.p('#include <stdlib.h>')
         cw.p('#include <string.h>')