sunrpc: flag transports as having congestion control

NFSv4 requires a transport protocol with congestion control in most
cases.

On an IP network, that means that NFSv4 over UDP should be forbidden.

The situation with RDMA is a bit more nuanced, but most RDMA transports
are suitable for this. For now, we assume that all RDMA transports are
suitable, but we may need to revise that at some point.

Signed-off-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>

3 files changed, 10 insertions, 0 deletions

diff --git a/include/linux/sunrpc/svc_xprt.h b/include/linux/sunrpc/svc_xprt.h
index 7440290f64ac..ddb7f94a9d06 100644
--- a/include/linux/sunrpc/svc_xprt.h
+++ b/include/linux/sunrpc/svc_xprt.h
@@ -67,6 +67,7 @@ struct svc_xprt {
 #define XPT_CACHE_AUTH  11              /* cache auth info */
 #define XPT_LOCAL       12              /* connection from loopback interface */
 #define XPT_KILL_TEMP   13              /* call xpo_kill_temp_xprt before closing */
+#define XPT_CONG_CTRL   14              /* has congestion control */
 
         struct svc_serv         *xpt_server;    /* service for transport */
         atomic_t                xpt_reserved;   /* space on outq that is rsvd */
diff --git a/net/sunrpc/svcsock.c b/net/sunrpc/svcsock.c
index de066acdb34e..1956b8b96b2d 100644
--- a/net/sunrpc/svcsock.c
+++ b/net/sunrpc/svcsock.c
@@ -1306,6 +1306,7 @@ static void svc_tcp_init(struct svc_sock *svsk, struct svc_serv *serv)
         svc_xprt_init(sock_net(svsk->sk_sock->sk), &svc_tcp_class,
                       &svsk->sk_xprt, serv);
         set_bit(XPT_CACHE_AUTH, &svsk->sk_xprt.xpt_flags);
+        set_bit(XPT_CONG_CTRL, &svsk->sk_xprt.xpt_flags);
         if (sk->sk_state == TCP_LISTEN) {
                 dprintk("setting up TCP socket for listening\n");
                 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 ab2fd5377f94..9d9e4e16080f 100644
--- a/net/sunrpc/xprtrdma/svc_rdma_transport.c
+++ b/net/sunrpc/xprtrdma/svc_rdma_transport.c
@@ -569,6 +569,14 @@ static struct svcxprt_rdma *rdma_create_xprt(struct svc_serv *serv,
         spin_lock_init(&cma_xprt->sc_ctxt_lock);
         spin_lock_init(&cma_xprt->sc_map_lock);
 
+        /*
+         * Note that this implies that the underlying transport support
+         * has some form of congestion control (see RFC 7530 section 3.1
+         * paragraph 2). For now, we assume that all supported RDMA
+         * transports are suitable here.
+         */
+        set_bit(XPT_CONG_CTRL, &cma_xprt->sc_xprt.xpt_flags);
+
         if (listener)
                 set_bit(XPT_LISTENER, &cma_xprt->sc_xprt.xpt_flags);