[PATCH v2 4/7] SUNRPC: Mark connection-oriented transports on svc_xprt

[Chuck Lever <cel@kernel.org>]

A TCP or RDMA svc_xprt carries one client's request stream, delivered
reliably and in order, so a later request on it indicates that earlier
replies reached the client. A UDP svc_xprt is shared by every peer and
offers no such signal.

Add an XPT_ORDERED flag, set by the TCP and RDMA init paths and clear
for UDP, so the NFSD duplicate reply cache can confine implied-ACK
eviction to transports where the signal holds.

The flag has a cost on svcrdma. handle_connect_req() zeroes the remote
port in the DRC key so a cached reply survives a reconnect, and
implied-ACK eviction can retire such an entry while the original
connection is still up. TCP gives up the same thing whenever a client
re-binds its reserved port, so this follows from the eviction policy
rather than from RDMA.

Signed-off-by: Chuck Lever <cel@kernel.org>
---
 include/linux/sunrpc/svc_xprt.h          | 1 +
 include/trace/events/sunrpc.h            | 1 +
 net/sunrpc/svcsock.c                     | 1 +
 net/sunrpc/xprtrdma/svc_rdma_transport.c | 1 +
 4 files changed, 4 insertions(+)

diff --git a/include/linux/sunrpc/svc_xprt.h b/include/linux/sunrpc/svc_xprt.h
index 53ed073640a6..ebab18e403b2 100644
--- a/include/linux/sunrpc/svc_xprt.h
+++ b/include/linux/sunrpc/svc_xprt.h
@@ -99,6 +99,7 @@ enum {
 	XPT_LOCAL,		/* connection from loopback interface */
 	XPT_KILL_TEMP,		/* call xpo_kill_temp_xprt before closing */
 	XPT_CONG_CTRL,		/* has congestion control */
+	XPT_ORDERED,		/* connection-oriented, in-order delivery */
 	XPT_HANDSHAKE,		/* xprt requests a handshake */
 	XPT_TLS_SESSION,	/* transport-layer security established */
 	XPT_PEER_AUTH,		/* peer has been authenticated */
diff --git a/include/trace/events/sunrpc.h b/include/trace/events/sunrpc.h
index 180346e520ff..2154fbe69945 100644
--- a/include/trace/events/sunrpc.h
+++ b/include/trace/events/sunrpc.h
@@ -1931,6 +1931,7 @@ TRACE_EVENT(svc_stats_latency,
 	svc_xprt_flag(LOCAL)						\
 	svc_xprt_flag(KILL_TEMP)					\
 	svc_xprt_flag(CONG_CTRL)					\
+	svc_xprt_flag(ORDERED)						\
 	svc_xprt_flag(HANDSHAKE)					\
 	svc_xprt_flag(TLS_SESSION)					\
 	svc_xprt_flag(PEER_AUTH)					\
diff --git a/net/sunrpc/svcsock.c b/net/sunrpc/svcsock.c
index 840bec53e1ee..97a592ddeb48 100644
--- a/net/sunrpc/svcsock.c
+++ b/net/sunrpc/svcsock.c
@@ -1486,6 +1486,7 @@ static bool svc_tcp_init(struct svc_sock *svsk, struct svc_serv *serv)
 		return false;
 	set_bit(XPT_CACHE_AUTH, &svsk->sk_xprt.xpt_flags);
 	set_bit(XPT_CONG_CTRL, &svsk->sk_xprt.xpt_flags);
+	set_bit(XPT_ORDERED, &svsk->sk_xprt.xpt_flags);
 	if (sk->sk_state == TCP_LISTEN) {
 		strcpy(svsk->sk_xprt.xpt_remotebuf, "listener");
 		set_bit(XPT_LISTENER, &svsk->sk_xprt.xpt_flags);
diff --git a/net/sunrpc/xprtrdma/svc_rdma_transport.c b/net/sunrpc/xprtrdma/svc_rdma_transport.c
index fabdfd891a41..5d39fce231a3 100644
--- a/net/sunrpc/xprtrdma/svc_rdma_transport.c
+++ b/net/sunrpc/xprtrdma/svc_rdma_transport.c
@@ -218,6 +218,7 @@ static struct svcxprt_rdma *svc_rdma_create_xprt(struct svc_serv *serv,
 	 * transports are suitable here.
 	 */
 	set_bit(XPT_CONG_CTRL, &cma_xprt->sc_xprt.xpt_flags);
+	set_bit(XPT_ORDERED, &cma_xprt->sc_xprt.xpt_flags);
 
 	return cma_xprt;
 }

-- 
2.55.0