tools: ynl-gen: add support for exact-len validation

add support for 'exact-len' validation on netlink attributes.

Link: https://github.com/multipath-tcp/mptcp_net-next/issues/340Acked-by: Matthieu Baerts <matttbe@kernel.org>
Signed-off-by: Davide Caratti <dcaratti@redhat.com>
Signed-off-by: Mat Martineau <martineau@kernel.org>
Link: https://lore.kernel.org/r/20231023-send-net-next-20231023-1-v2-2-16b1f701f900@kernel.orgSigned-off-by: Jakub Kicinski <kuba@kernel.org>

Documentation/netlink/genetlink-c.yaml

@@ -199,6 +199,9 @@ properties:
                   max-len:
                     description: Max length for a string or a binary attribute.
                     $ref: '#/$defs/len-or-define'
+                  exact-len:
+                    description: Exact length for a string or a binary attribute.
+                    $ref: '#/$defs/len-or-define'
               sub-type: *attr-type
               display-hint: &display-hint
                 description: |

Documentation/netlink/genetlink-legacy.yaml

@@ -242,6 +242,9 @@ properties:
                   max-len:
                     description: Max length for a string or a binary attribute.
                     $ref: '#/$defs/len-or-define'
+                  exact-len:
+                    description: Exact length for a string or a binary attribute.
+                    $ref: '#/$defs/len-or-define'
               sub-type: *attr-type
               display-hint: *display-hint
               # Start genetlink-c

Documentation/netlink/genetlink.yaml

@@ -172,6 +172,9 @@ properties:
                   max-len:
                     description: Max length for a string or a binary attribute.
                     $ref: '#/$defs/len-or-define'
+                  exact-len:
+                    description: Exact length for a string or a binary attribute.
+                    $ref: '#/$defs/len-or-define'
               sub-type: *attr-type
               display-hint: &display-hint
                 description: |

Documentation/netlink/netlink-raw.yaml

@@ -240,6 +240,9 @@ properties:
                   max-len:
                     description: Max length for a string or a binary attribute.
                     $ref: '#/$defs/len-or-define'
+                  exact-len:
+                    description: Exact length for a string or a binary attribute.
+                    $ref: '#/$defs/len-or-define'
               sub-type: *attr-type
               display-hint: *display-hint
               # Start genetlink-c

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

@@ -410,10 +410,13 @@ class TypeString(Type):
         return f'.type = YNL_PT_NUL_STR, '
 
     def _attr_policy(self, policy):
-        mem = '{ .type = ' + policy
-        if 'max-len' in self.checks:
-            mem += ', .len = ' + str(self.get_limit('max-len'))
-        mem += ', }'
+        if 'exact-len' in self.checks:
+            mem = 'NLA_POLICY_EXACT_LEN(' + str(self.checks['exact-len']) + ')'
+        else:
+            mem = '{ .type = ' + policy
+            if 'max-len' in self.checks:
+                mem += ', .len = ' + str(self.get_limit('max-len'))
+            mem += ', }'
         return mem
 
     def attr_policy(self, cw):
@@ -459,14 +462,17 @@ class TypeBinary(Type):
         return f'.type = YNL_PT_BINARY,'
 
     def _attr_policy(self, policy):
-        mem = '{ '
-        if len(self.checks) == 1 and 'min-len' in self.checks:
-            mem += '.len = ' + str(self.get_limit('min-len'))
-        elif len(self.checks) == 0:
-            mem += '.type = NLA_BINARY'
+        if 'exact-len' in self.checks:
+            mem = 'NLA_POLICY_EXACT_LEN(' + str(self.checks['exact-len']) + ')'
         else:
-            raise Exception('One or more of binary type checks not implemented, yet')
-        mem += ', }'
+            mem = '{ '
+            if len(self.checks) == 1 and 'min-len' in self.checks:
+                mem += '.len = ' + str(self.get_limit('min-len'))
+            elif len(self.checks) == 0:
+                mem += '.type = NLA_BINARY'
+            else:
+                raise Exception('One or more of binary type checks not implemented, yet')
+            mem += ', }'
         return mem
 
     def attr_put(self, ri, var):