net/connector: Add const qualifier to cb_id

The connector driver never modifies any cb_id passed to it, so add a const
qualifier to those arguments so callers can declare their struct cb_id as a
constant object.

Fixes build warnings like these when passing a constant struct cb_id:

warning: passing argument 1 of ‘cn_add_callback’ discards ‘const’ qualifier from pointer target

Signed-off-by: Geoff Levand <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Jakub Kicinski <[e-mail]>

Documentation/driver-api/connector.rst

···
 netlink based networking for inter-process communication in a significantly
 easier way::
 
-  int cn_add_callback(struct cb_id *id, char *name, void (*callback) (struct cn_msg *, struct netlink_skb_parms *));
+  int cn_add_callback(const struct cb_id *id, char *name, void (*callback) (struct cn_msg *, struct netlink_skb_parms *));
   void cn_netlink_send_mult(struct cn_msg *msg, u16 len, u32 portid, u32 __group, int gfp_mask);
   void cn_netlink_send(struct cn_msg *msg, u32 portid, u32 __group, int gfp_mask);
 

drivers/connector/cn_queue.c

···
 
 static struct cn_callback_entry *
 cn_queue_alloc_callback_entry(struct cn_queue_dev *dev, const char *name,
-			      struct cb_id *id,
+			      const struct cb_id *id,
 			      void (*callback)(struct cn_msg *,
 					       struct netlink_skb_parms *))
 {
···
 	kfree(cbq);
 }
 
-int cn_cb_equal(struct cb_id *i1, struct cb_id *i2)
+int cn_cb_equal(const struct cb_id *i1, const struct cb_id *i2)
 {
 	return ((i1->idx == i2->idx) && (i1->val == i2->val));
 }
 
 int cn_queue_add_callback(struct cn_queue_dev *dev, const char *name,
-			  struct cb_id *id,
+			  const struct cb_id *id,
 			  void (*callback)(struct cn_msg *,
 					   struct netlink_skb_parms *))
 {
···
 	return 0;
 }
 
-void cn_queue_del_callback(struct cn_queue_dev *dev, struct cb_id *id)
+void cn_queue_del_callback(struct cn_queue_dev *dev, const struct cb_id *id)
 {
 	struct cn_callback_entry *cbq, *n;
 	int found = 0;

drivers/connector/connector.c

···
  *
  * May sleep.
  */
-int cn_add_callback(struct cb_id *id, const char *name,
+int cn_add_callback(const struct cb_id *id, const char *name,
 		    void (*callback)(struct cn_msg *,
 				     struct netlink_skb_parms *))
 {
···
  *
  * May sleep while waiting for reference counter to become zero.
  */
-void cn_del_callback(struct cb_id *id)
+void cn_del_callback(const struct cb_id *id)
 {
 	struct cn_dev *dev = &cdev;
 

include/linux/connector.h

···
  * @callback:	connector's callback.
  * 		parameters are %cn_msg and the sender's credentials
  */
-int cn_add_callback(struct cb_id *id, const char *name,
+int cn_add_callback(const struct cb_id *id, const char *name,
 		    void (*callback)(struct cn_msg *, struct netlink_skb_parms *));
 /**
  * cn_del_callback() - Unregisters new callback with connector core.
  *
  * @id:		unique connector's user identifier.
  */
-void cn_del_callback(struct cb_id *id);
+void cn_del_callback(const struct cb_id *id);
 
 
 /**
···
 int cn_netlink_send(struct cn_msg *msg, u32 portid, u32 group, gfp_t gfp_mask);
 
 int cn_queue_add_callback(struct cn_queue_dev *dev, const char *name,
-			  struct cb_id *id,
+			  const struct cb_id *id,
 			  void (*callback)(struct cn_msg *, struct netlink_skb_parms *));
-void cn_queue_del_callback(struct cn_queue_dev *dev, struct cb_id *id);
+void cn_queue_del_callback(struct cn_queue_dev *dev, const struct cb_id *id);
 void cn_queue_release_callback(struct cn_callback_entry *);
 
 struct cn_queue_dev *cn_queue_alloc_dev(const char *name, struct sock *);
 void cn_queue_free_dev(struct cn_queue_dev *dev);
 
-int cn_cb_equal(struct cb_id *, struct cb_id *);
+int cn_cb_equal(const struct cb_id *, const struct cb_id *);
 
 #endif				/* __CONNECTOR_H */