+/**
+ * xprt_reserve_xprt - serialize write access to transports
+ * @task: task that is requesting access to the transport
+ *
+ * This prevents mixing the payload of separate requests, and prevents
+ * transport connects from colliding with writes. No congestion control
+ * is provided.
+ */
+int xprt_reserve_xprt(struct rpc_task *task)
+{
+ struct rpc_xprt *xprt = task->tk_xprt;
+ struct rpc_rqst *req = task->tk_rqstp;
+
+ if (test_and_set_bit(XPRT_LOCKED, &xprt->state)) {
+ if (task == xprt->snd_task)
+ return 1;
+ if (task == NULL)
+ return 0;
+ goto out_sleep;
+ }
+ xprt->snd_task = task;
+ if (req) {
+ req->rq_bytes_sent = 0;
+ req->rq_ntrans++;
+ }
+ return 1;
+
+out_sleep:
+ dprintk("RPC: %4d failed to lock transport %p\n",
+ task->tk_pid, xprt);
+ task->tk_timeout = 0;
+ task->tk_status = -EAGAIN;
+ if (req && req->rq_ntrans)
+ rpc_sleep_on(&xprt->resend, task, NULL, NULL);
+ else
+ rpc_sleep_on(&xprt->sending, task, NULL, NULL);
+ return 0;
+}
+