NFS: disconnect before retrying NFSv4 requests over TCP

RFC3530 section 3.1.1 states an NFSv4 client MUST NOT send a request
twice on the same connection unless it is the NULL procedure.  Section
3.1.1 suggests that the client should disconnect and reconnect if it
wants to retry a request.

Implement this by adding an rpc_clnt flag that an ULP can use to
specify that the underlying transport should be disconnected on a
major timeout.  The NFSv4 client asserts this new flag, and requests
no retries after a minor retransmit timeout.

Note that disconnecting on a retransmit is in general not safe to do
if the RPC client does not reuse the TCP port number when reconnecting.

See http://bugzilla.linux-nfs.org/show_bug.cgi?id=6

Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>

2 files changed, 12 insertions, 0 deletions

diff --git a/net/sunrpc/clnt.c b/net/sunrpc/clnt.c
index 393e70aee181..c21aa0a7f770 100644
--- a/net/sunrpc/clnt.c
+++ b/net/sunrpc/clnt.c
@@ -249,6 +249,8 @@ struct rpc_clnt *rpc_create(struct rpc_create_args *args)
                 clnt->cl_autobind = 1;
         if (args->flags & RPC_CLNT_CREATE_ONESHOT)
                 clnt->cl_oneshot = 1;
+        if (args->flags & RPC_CLNT_CREATE_DISCRTRY)
+                clnt->cl_discrtry = 1;
 
         return clnt;
 }
diff --git a/net/sunrpc/xprt.c b/net/sunrpc/xprt.c
index cf59f7d315d0..1975139b26e7 100644
--- a/net/sunrpc/xprt.c
+++ b/net/sunrpc/xprt.c
@@ -735,6 +735,16 @@ void xprt_transmit(struct rpc_task *task)
                         xprt_reset_majortimeo(req);
                         /* Turn off autodisconnect */
                         del_singleshot_timer_sync(&xprt->timer);
+                } else {
+                        /* If all request bytes have been sent,
+                         * then we must be retransmitting this one */
+                        if (!req->rq_bytes_sent) {
+                                if (task->tk_client->cl_discrtry) {
+                                        xprt_disconnect(xprt);
+                                        task->tk_status = -ENOTCONN;
+                                        return;
+                                }
+                        }
                 }
         } else if (!req->rq_bytes_sent)
                 return;