rds: transport module should be auto loaded when transport is set

This enhancement auto loads transport module when the transport
is set via SO_RDS_TRANSPORT socket option.
Reviewed-by: Ka-Cheong Poon <ka-cheong.poon@oracle.com>
Reviewed-by: Håkon Bugge <haakon.bugge@oracle.com>
Signed-off-by: Rao Shoaib <rao.shoaib@oracle.com>
Signed-off-by: Somasundaram Krishnasamy <somasundaram.krishnasamy@oracle.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/uapi/linux/rds.h

@@ -64,10 +64,12 @@
 
 /* supported values for SO_RDS_TRANSPORT */
 #define	RDS_TRANS_IB	0
-#define	RDS_TRANS_IWARP	1
+#define	RDS_TRANS_GAP	1
 #define	RDS_TRANS_TCP	2
 #define RDS_TRANS_COUNT	3
 #define	RDS_TRANS_NONE	(~0)
+/* don't use RDS_TRANS_IWARP - it is deprecated */
+#define RDS_TRANS_IWARP RDS_TRANS_GAP
 
 /* IOCTLS commands for SOL_RDS */
 #define SIOCRDSSETTOS		(SIOCPROTOPRIVATE)

net/rds/transport.c

@@ -38,6 +38,12 @@
 #include "rds.h"
 #include "loop.h"
 
+static char * const rds_trans_modules[] = {
+	[RDS_TRANS_IB] = "rds_rdma",
+	[RDS_TRANS_GAP] = NULL,
+	[RDS_TRANS_TCP] = "rds_tcp",
+};
+
 static struct rds_transport *transports[RDS_TRANS_COUNT];
 static DECLARE_RWSEM(rds_trans_sem);
 
@@ -110,18 +116,20 @@ struct rds_transport *rds_trans_get(int t_type)
 {
 	struct rds_transport *ret = NULL;
 	struct rds_transport *trans;
-	unsigned int i;
 
 	down_read(&rds_trans_sem);
-	for (i = 0; i < RDS_TRANS_COUNT; i++) {
-		trans = transports[i];
-
-		if (trans && trans->t_type == t_type &&
-		    (!trans->t_owner || try_module_get(trans->t_owner))) {
-			ret = trans;
-			break;
-		}
+	trans = transports[t_type];
+	if (!trans) {
+		up_read(&rds_trans_sem);
+		if (rds_trans_modules[t_type])
+			request_module(rds_trans_modules[t_type]);
+		down_read(&rds_trans_sem);
+		trans = transports[t_type];
 	}
+	if (trans && trans->t_type == t_type &&
+	    (!trans->t_owner || try_module_get(trans->t_owner)))
+		ret = trans;
+
 	up_read(&rds_trans_sem);
 
 	return ret;