[PATCH net-next] netlink: specs: support conditional operations

[Jakub Kicinski <kuba@kernel.org>]

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.

Signed-off-by: Jakub Kicinski <kuba@kernel.org>
---
 Documentation/netlink/genetlink-c.yaml      |  5 +++++
 Documentation/netlink/genetlink-legacy.yaml |  5 +++++
 Documentation/netlink/genetlink.yaml        |  5 +++++
 tools/net/ynl/ynl-gen-c.py                  | 22 +++++++++++++++++++++
 4 files changed, 37 insertions(+)

diff --git a/Documentation/netlink/genetlink-c.yaml b/Documentation/netlink/genetlink-c.yaml
index 7ef2496d57c8..9d13bbb7ae47 100644
--- a/Documentation/netlink/genetlink-c.yaml
+++ b/Documentation/netlink/genetlink-c.yaml
@@ -295,6 +295,11 @@ additionalProperties: False
               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
diff --git a/Documentation/netlink/genetlink-legacy.yaml b/Documentation/netlink/genetlink-legacy.yaml
index cd5ebe39b52c..0daf40402a29 100644
--- a/Documentation/netlink/genetlink-legacy.yaml
+++ b/Documentation/netlink/genetlink-legacy.yaml
@@ -346,6 +346,11 @@ additionalProperties: False
               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
diff --git a/Documentation/netlink/genetlink.yaml b/Documentation/netlink/genetlink.yaml
index 501ed2e6c8ef..3283bf458ff1 100644
--- a/Documentation/netlink/genetlink.yaml
+++ b/Documentation/netlink/genetlink.yaml
@@ -264,6 +264,11 @@ additionalProperties: False
               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
diff --git a/tools/net/ynl/ynl-gen-c.py b/tools/net/ynl/ynl-gen-c.py
index 0fee68863db4..6eb32b2ef848 100755
--- a/tools/net/ynl/ynl-gen-c.py
+++ b/tools/net/ynl/ynl-gen-c.py
@@ -1162,6 +1162,7 @@ from lib import SpecFamily, SpecAttrSet, SpecAttr, SpecOperation, SpecEnumSet, S
         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 @@ from lib import SpecFamily, SpecAttrSet, SpecAttr, SpecOperation, SpecEnumSet, S
         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 @@ from lib import SpecFamily, SpecAttrSet, SpecAttr, SpecOperation, SpecEnumSet, S
             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 @@ _C_KW = {
 
 
 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 @@ _C_KW = {
             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 @@ _C_KW = {
                 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 @@ _C_KW = {
                 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()
-- 
2.41.0