rpc: allow xprt_class->setup to return a preexisting xprt

This allows us to reuse the xprt associated with a server connection if
one has already been set up.

Signed-off-by: J. Bruce Fields <bfields@redhat.com>

2 files changed, 12 insertions, 9 deletions

diff --git a/net/sunrpc/xprt.c b/net/sunrpc/xprt.c
index 749ad15ae305..856274d7e85c 100644
--- a/net/sunrpc/xprt.c
+++ b/net/sunrpc/xprt.c
@@ -1102,6 +1102,9 @@ found:
                                 -PTR_ERR(xprt));
                 return xprt;
         }
+        if (test_and_set_bit(XPRT_INITIALIZED, &xprt->state))
+                /* ->setup returned a pre-initialized xprt: */
+                return xprt;
 
         spin_lock_init(&xprt->transport_lock);
         spin_lock_init(&xprt->reserve_lock);
diff --git a/net/sunrpc/xprtsock.c b/net/sunrpc/xprtsock.c
index 0ef4dd4414ec..ee091c869fcd 100644
--- a/net/sunrpc/xprtsock.c
+++ b/net/sunrpc/xprtsock.c
@@ -2359,6 +2359,15 @@ static struct rpc_xprt *xs_setup_bc_tcp(struct xprt_create *args)
         struct svc_sock *bc_sock;
         struct rpc_xprt *ret;
 
+        if (args->bc_xprt->xpt_bc_xprt) {
+                /*
+                 * This server connection already has a backchannel
+                 * export; we can't create a new one, as we wouldn't be
+                 * able to match replies based on xid any more.  So,
+                 * reuse the already-existing one:
+                 */
+                 return args->bc_xprt->xpt_bc_xprt;
+        }
         xprt = xs_setup_xprt(args, xprt_tcp_slot_table_entries);
         if (IS_ERR(xprt))
                 return xprt;
@@ -2397,15 +2406,6 @@ static struct rpc_xprt *xs_setup_bc_tcp(struct xprt_create *args)
                         xprt->address_strings[RPC_DISPLAY_PROTO]);
 
         /*
-         * The backchannel uses the same socket connection as the
-         * forechannel
-         */
-        if (args->bc_xprt->xpt_bc_xprt) {
-                /* XXX: actually, want to catch this case... */
-                ret = ERR_PTR(-EINVAL);
-                goto out_err;
-        }
-        /*
          * Once we've associated a backchannel xprt with a connection,
          * we want to keep it around as long as long as the connection
          * lasts, in case we need to start using it for a backchannel