netlink: specs: support conditional operations

Page pool code is compiled conditionally, but the operations
are part of the shared netlink family. We can handle this
by reporting empty list of pools or -EOPNOTSUPP / -ENOSYS
but the cleanest way seems to be removing the ops completely
at compilation time. That way user can see that the page
pool ops are not present using genetlink introspection.
Same way they'd check if the kernel is "new enough" to
support the ops.

Extend the specs with the ability to specify the config
condition under which op (and its policies, etc.) should
be hidden.

Reviewed-by: Jiri Pirko <jiri@nvidia.com>
Link: https://lore.kernel.org/r/20231025162253.133159-1-kuba@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Documentation/netlink/genetlink-c.yaml

@@ -295,6 +295,11 @@ properties:
               type: array
               items:
                 enum: [ strict, dump, dump-strict ]
+            config-cond:
+              description: |
+                Name of the kernel config option gating the presence of
+                the operation, without the 'CONFIG_' prefix.
+              type: string
             do: &subop-type
               description: Main command handler.
               type: object

Documentation/netlink/genetlink-legacy.yaml

@@ -346,6 +346,11 @@ properties:
               type: array
               items:
                 enum: [ strict, dump, dump-strict ]
+            config-cond:
+              description: |
+                Name of the kernel config option gating the presence of
+                the operation, without the 'CONFIG_' prefix.
+              type: string
             # Start genetlink-legacy
             fixed-header: *fixed-header
             # End genetlink-legacy

Documentation/netlink/genetlink.yaml

@@ -264,6 +264,11 @@ properties:
               type: array
               items:
                 enum: [ strict, dump, dump-strict ]
+            config-cond:
+              description: |
+                Name of the kernel config option gating the presence of
+                the operation, without the 'CONFIG_' prefix.
+              type: string
             do: &subop-type
               description: Main command handler.
               type: object

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

@@ -1162,6 +1162,7 @@ def __init__(self, nlib, out_file=None):
         self._block_end = False
         self._silent_block = False
         self._ind = 0
+        self._ifdef_block = None
         if out_file is None:
             self._out = os.sys.stdout
         else:
@@ -1202,6 +1203,8 @@ def p(self, line, add_ind=0):
         if self._silent_block:
             ind += 1
         self._silent_block = line.endswith(')') and CodeWriter._is_cond(line)
+        if line[0] == '#':
+            ind = 0
         if add_ind:
             ind += add_ind
         self._out.write('\t' * ind + line + '\n')
@@ -1328,6 +1331,19 @@ def write_struct_init(self, members):
             line += '= ' + str(one[1]) + ','
             self.p(line)
 
+    def ifdef_block(self, config):
+        config_option = None
+        if config:
+            config_option = 'CONFIG_' + c_upper(config)
+        if self._ifdef_block == config_option:
+            return
+
+        if self._ifdef_block:
+            self.p('#endif /* ' + self._ifdef_block + ' */')
+        if config_option:
+            self.p('#ifdef ' + config_option)
+        self._ifdef_block = config_option
+
 
 scalars = {'u8', 'u16', 'u32', 'u64', 's32', 's64', 'uint', 'sint'}
 
@@ -2006,10 +2022,13 @@ def print_req_policy_fwd(cw, struct, ri=None, terminate=True):
 
 
 def print_req_policy(cw, struct, ri=None):
+    if ri and ri.op:
+        cw.ifdef_block(ri.op.get('config-cond', None))
     print_req_policy_fwd(cw, struct, ri=ri, terminate=False)
     for _, arg in struct.member_list():
         arg.attr_policy(cw)
     cw.p("};")
+    cw.ifdef_block(None)
     cw.nl()
 
 
@@ -2127,6 +2146,7 @@ def print_kernel_op_table(family, cw):
             if op.is_async:
                 continue
 
+            cw.ifdef_block(op.get('config-cond', None))
             cw.block_start()
             members = [('cmd', op.enum_name)]
             if 'dont-validate' in op:
@@ -2157,6 +2177,7 @@ def print_kernel_op_table(family, cw):
                 if op.is_async or op_mode not in op:
                     continue
 
+                cw.ifdef_block(op.get('config-cond', None))
                 cw.block_start()
                 members = [('cmd', op.enum_name)]
                 if 'dont-validate' in op:
@@ -2192,6 +2213,7 @@ def print_kernel_op_table(family, cw):
                 members.append(('flags', ' | '.join([c_upper('genl-' + x) for x in flags])))
                 cw.write_struct_init(members)
                 cw.block_end(line=',')
+    cw.ifdef_block(None)
 
     cw.block_end(line=';')
     cw.nl()