[NETFILTER]: more verbose return codes from nf_{log,queue}

This adds EEXIST to distinguish between the following return values:
0: 	nobody was registered, registration successful
EEXIST:	the exact same handler was already registered, no registration
	required
EBUSY:	somebody else is registered, registration unsuccessful.
Signed-off-by: Harald Welte <laforge@netfilter.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/netfilter/nf_log.c

@@ -18,6 +18,8 @@
 static struct nf_logger *nf_logging[NPROTO]; /* = NULL */
 static DEFINE_SPINLOCK(nf_log_lock);
 
+/* return EBUSY if somebody else is registered, EEXIST if the same logger
+ * is registred, 0 on success. */
 int nf_log_register(int pf, struct nf_logger *logger)
 {
 	int ret = -EBUSY;
@@ -28,7 +30,9 @@ int nf_log_register(int pf, struct nf_logger *logger)
 	if (!nf_logging[pf]) {
 		rcu_assign_pointer(nf_logging[pf], logger);
 		ret = 0;
-	}
+	} else if (nf_logging[pf] == logger)
+		ret = -EEXIST;
+
 	spin_unlock(&nf_log_lock);
 	return ret;
 }		

net/netfilter/nf_queue.c

@@ -20,6 +20,8 @@ static struct nf_queue_rerouter *queue_rerouter;
 
 static DEFINE_RWLOCK(queue_handler_lock);
 
+/* return EBUSY when somebody else is registered, return EEXIST if the
+ * same handler is registered, return 0 in case of success. */
 int nf_register_queue_handler(int pf, struct nf_queue_handler *qh)
 {      
 	int ret;
@@ -28,7 +30,9 @@ int nf_register_queue_handler(int pf, struct nf_queue_handler *qh)
 		return -EINVAL;
 
 	write_lock_bh(&queue_handler_lock);
-	if (queue_handler[pf])
+	if (queue_handler[pf] == qh)
+		ret = -EEXIST;
+	else if (queue_handler[pf])
 		ret = -EBUSY;
 	else {
 		queue_handler[pf] = qh;