[PATCH RFC 08/15] SUNRPC: Add RPC_TASK_CORK flag

[Chuck Lever <chuck.lever@oracle.com>]

Introduce a mechanism to cause xprt_transmit() to break out of its
sending loop at a specific rpc_rqst, rather than draining the whole
transmit queue.

This enables the client to send just an RPC TLS probe and then wait
for the response before proceeding with the rest of the queue.

Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
---
 include/linux/sunrpc/sched.h  |    2 ++
 include/trace/events/sunrpc.h |    1 +
 net/sunrpc/xprt.c             |    2 ++
 3 files changed, 5 insertions(+)

diff --git a/include/linux/sunrpc/sched.h b/include/linux/sunrpc/sched.h
index 599133fb3c63..f8c09638fa69 100644
--- a/include/linux/sunrpc/sched.h
+++ b/include/linux/sunrpc/sched.h
@@ -125,6 +125,7 @@ struct rpc_task_setup {
 #define RPC_TASK_TLSCRED		0x00000008	/* Use AUTH_TLS credential */
 #define RPC_TASK_NULLCREDS		0x00000010	/* Use AUTH_NULL credential */
 #define RPC_CALL_MAJORSEEN		0x00000020	/* major timeout seen */
+#define RPC_TASK_CORK			0x00000040	/* cork the xmit queue */
 #define RPC_TASK_DYNAMIC		0x00000080	/* task was kmalloc'ed */
 #define	RPC_TASK_NO_ROUND_ROBIN		0x00000100	/* send requests on "main" xprt */
 #define RPC_TASK_SOFT			0x00000200	/* Use soft timeouts */
@@ -137,6 +138,7 @@ struct rpc_task_setup {
 
 #define RPC_IS_ASYNC(t)		((t)->tk_flags & RPC_TASK_ASYNC)
 #define RPC_IS_SWAPPER(t)	((t)->tk_flags & RPC_TASK_SWAPPER)
+#define RPC_IS_CORK(t)		((t)->tk_flags & RPC_TASK_CORK)
 #define RPC_IS_SOFT(t)		((t)->tk_flags & (RPC_TASK_SOFT|RPC_TASK_TIMEOUT))
 #define RPC_IS_SOFTCONN(t)	((t)->tk_flags & RPC_TASK_SOFTCONN)
 #define RPC_WAS_SENT(t)		((t)->tk_flags & RPC_TASK_SENT)
diff --git a/include/trace/events/sunrpc.h b/include/trace/events/sunrpc.h
index 811187c47ebb..e8d6adff1a50 100644
--- a/include/trace/events/sunrpc.h
+++ b/include/trace/events/sunrpc.h
@@ -312,6 +312,7 @@ TRACE_EVENT(rpc_request,
 		{ RPC_TASK_TLSCRED, "TLSCRED" },			\
 		{ RPC_TASK_NULLCREDS, "NULLCREDS" },			\
 		{ RPC_CALL_MAJORSEEN, "MAJORSEEN" },			\
+		{ RPC_TASK_CORK, "CORK" },				\
 		{ RPC_TASK_DYNAMIC, "DYNAMIC" },			\
 		{ RPC_TASK_NO_ROUND_ROBIN, "NO_ROUND_ROBIN" },		\
 		{ RPC_TASK_SOFT, "SOFT" },				\
diff --git a/net/sunrpc/xprt.c b/net/sunrpc/xprt.c
index 86d62cffba0d..4b303b945b51 100644
--- a/net/sunrpc/xprt.c
+++ b/net/sunrpc/xprt.c
@@ -1622,6 +1622,8 @@ xprt_transmit(struct rpc_task *task)
 		if (xprt_request_data_received(task) &&
 		    !test_bit(RPC_TASK_NEED_XMIT, &task->tk_runstate))
 			break;
+		if (RPC_IS_CORK(task))
+			break;
 		cond_resched_lock(&xprt->queue_lock);
 	}
 	spin_unlock(&xprt->queue_lock);