RDS: Add GET_MR_FOR_DEST sockopt

RDS currently supports a GET_MR sockopt to establish a
memory region (MR) for a chunk of memory. However, the fastreg
method ties a MR to a particular destination. The GET_MR_FOR_DEST
sockopt allows the remote machine to be specified, and thus
support for fastreg (aka FRWRs).

Note that this patch does *not* do all of this - it simply
implements the new sockopt in terms of the old one, so applications
can begin to use the new sockopt in preparation for cutover to
FRWRs.
Signed-off-by: Andy Grover <andy.grover@oracle.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/linux/rds.h

@@ -56,6 +56,7 @@
 /* deprecated: RDS_BARRIER 4 */
 #define RDS_RECVERR			5
 #define RDS_CONG_MONITOR		6
+#define RDS_GET_MR_FOR_DEST		7
 
 /*
  * Control message types for SOL_RDS.
@@ -224,6 +225,13 @@ struct rds_get_mr_args {
 	uint64_t	flags;
 };
 
+struct rds_get_mr_for_dest_args {
+	struct sockaddr_storage	dest_addr;
+	struct rds_iovec 	vec;
+	u_int64_t		cookie_addr;
+	uint64_t		flags;
+};
+
 struct rds_free_mr_args {
 	rds_rdma_cookie_t cookie;
 	u_int64_t	flags;

net/rds/af_rds.c

@@ -265,6 +265,9 @@ static int rds_setsockopt(struct socket *sock, int level, int optname,
 	case RDS_GET_MR:
 		ret = rds_get_mr(rs, optval, optlen);
 		break;
+	case RDS_GET_MR_FOR_DEST:
+		ret = rds_get_mr_for_dest(rs, optval, optlen);
+		break;
 	case RDS_FREE_MR:
 		ret = rds_free_mr(rs, optval, optlen);
 		break;

net/rds/rdma.c

@@ -317,6 +317,30 @@ int rds_get_mr(struct rds_sock *rs, char __user *optval, int optlen)
 	return __rds_rdma_map(rs, &args, NULL, NULL);
 }
 
+int rds_get_mr_for_dest(struct rds_sock *rs, char __user *optval, int optlen)
+{
+	struct rds_get_mr_for_dest_args args;
+	struct rds_get_mr_args new_args;
+
+	if (optlen != sizeof(struct rds_get_mr_for_dest_args))
+		return -EINVAL;
+
+	if (copy_from_user(&args, (struct rds_get_mr_for_dest_args __user *)optval,
+			   sizeof(struct rds_get_mr_for_dest_args)))
+		return -EFAULT;
+
+	/*
+	 * Initially, just behave like get_mr().
+	 * TODO: Implement get_mr as wrapper around this
+	 *	 and deprecate it.
+	 */
+	new_args.vec = args.vec;
+	new_args.cookie_addr = args.cookie_addr;
+	new_args.flags = args.flags;
+
+	return __rds_rdma_map(rs, &new_args, NULL, NULL);
+}
+
 /*
  * Free the MR indicated by the given R_Key
  */

net/rds/rdma.h

@@ -61,6 +61,7 @@ static inline u32 rds_rdma_cookie_offset(rds_rdma_cookie_t cookie)
 }
 
 int rds_get_mr(struct rds_sock *rs, char __user *optval, int optlen);
+int rds_get_mr_for_dest(struct rds_sock *rs, char __user *optval, int optlen);
 int rds_free_mr(struct rds_sock *rs, char __user *optval, int optlen);
 void rds_rdma_drop_keys(struct rds_sock *rs);
 int rds_cmsg_rdma_args(struct rds_sock *rs, struct rds_message *rm,