[PATCH] RPC: expose API for serializing access to RPC transports

 The next several patches introduce an API that allows transports to
 choose whether the RPC client provides congestion control or whether
 the transport itself provides it.

 The first method we abstract is the one that serializes access to the
 RPC transport to prevent the bytes from different requests from mingling
 together.  This method provides proper request serialization and the
 opportunity to prevent new requests from being started because the
 transport is congested.

 The normal situation is for the transport to handle congestion control
 itself.  Although NFS over UDP was first, it has been recognized after
 years of experience that having the transport provide congestion control
 is much better than doing it in the RPC client.  Thus TCP, and probably
 every future transport implementation, will use the default method,
 xprt_lock_write, provided in xprt.c, which does not provide any kind
 of congestion control.  UDP can continue using the xprt.c-provided
 Van Jacobson congestion avoidance implementation.

 Test-plan:
 Use WAN simulation to cause sporadic bursty packet loss.  Look for significant
 regression in performance or client stability.

 Signed-off-by: Chuck Lever <cel@netapp.com>
 Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>

1 files changed, 3 insertions, 0 deletions

diff --git a/include/linux/sunrpc/xprt.h b/include/linux/sunrpc/xprt.h
index ac08e99a81cb..eee1c6877851 100644
--- a/include/linux/sunrpc/xprt.h
+++ b/include/linux/sunrpc/xprt.h
@@ -132,6 +132,7 @@ struct rpc_xprt;
 
 struct rpc_xprt_ops {
         void            (*set_buffer_size)(struct rpc_xprt *xprt);
+        int             (*reserve_xprt)(struct rpc_task *task);
         void            (*connect)(struct rpc_task *task);
         int             (*send_request)(struct rpc_task *task);
         void            (*set_retrans_timeout)(struct rpc_task *task);
@@ -232,6 +233,8 @@ void			xprt_set_timeout(struct rpc_timeout *to, unsigned int retr, unsigned long
  */
 void                    xprt_connect(struct rpc_task *task);
 void                    xprt_reserve(struct rpc_task *task);
+int                     xprt_reserve_xprt(struct rpc_task *task);
+int                     xprt_reserve_xprt_cong(struct rpc_task *task);
 int                     xprt_prepare_transmit(struct rpc_task *task);
 void                    xprt_transmit(struct rpc_task *task);
 int                     xprt_adjust_timeout(struct rpc_rqst *req);