Index: head/lib/libc/sys/send.2
===================================================================
--- head/lib/libc/sys/send.2
+++ head/lib/libc/sys/send.2
@@ -28,7 +28,7 @@
 .\"     From: @(#)send.2	8.2 (Berkeley) 2/21/94
 .\" $FreeBSD$
 .\"
-.Dd August 19, 2018
+.Dd January 4, 2019
 .Dt SEND 2
 .Os
 .Sh NAME
@@ -121,7 +121,8 @@
 .Bd -literal
 #define	MSG_OOB		0x00001 /* process out-of-band data */
 #define	MSG_DONTROUTE	0x00004 /* bypass routing, use direct interface */
-#define MSG_EOR		0x00008 /* data completes record */
+#define	MSG_EOR		0x00008 /* data completes record */
+#define	MSG_DONTWAIT	0x00080 /* do not block */
 #define	MSG_EOF		0x00100 /* data completes transaction */
 #define	MSG_NOSIGNAL	0x20000 /* do not generate SIGPIPE on EOF */
 .Ed
@@ -138,6 +139,9 @@
 .Dv MSG_EOR
 is used to indicate a record mark for protocols which support the
 concept.
+The
+.Dv MSG_DONTWAIT
+flag request the call to return when it would block otherwise.
 .Dv MSG_EOF
 requests that the sender side of a socket be shut down, and that an
 appropriate indication be sent at the end of the specified data;
@@ -201,8 +205,9 @@
 The socket requires that message be sent atomically,
 and the size of the message to be sent made this impossible.
 .It Bq Er EAGAIN
-The socket is marked non-blocking and the requested operation
-would block.
+The socket is marked non-blocking, or
+.Dv MSG_DONTWAIT
+is specified, and the requested operation would block.
 .It Bq Er ENOBUFS
 The system was unable to allocate an internal buffer.
 The operation may succeed when buffers become available.
Index: head/sys/kern/uipc_socket.c
===================================================================
--- head/sys/kern/uipc_socket.c
+++ head/sys/kern/uipc_socket.c
@@ -1522,7 +1522,8 @@
 		}
 		if (space < resid + clen &&
 		    (atomic || space < so->so_snd.sb_lowat || space < clen)) {
-			if ((so->so_state & SS_NBIO) || (flags & MSG_NBIO)) {
+			if ((so->so_state & SS_NBIO) ||
+			    (flags & (MSG_NBIO | MSG_DONTWAIT)) != 0) {
 				SOCKBUF_UNLOCK(&so->so_snd);
 				error = EWOULDBLOCK;
 				goto release;
Index: head/sys/netinet/sctp_output.c
===================================================================
--- head/sys/netinet/sctp_output.c
+++ head/sys/netinet/sctp_output.c
@@ -12836,7 +12836,7 @@
 		}
 	}
 	if (SCTP_SO_IS_NBIO(so)
-	    || (flags & MSG_NBIO)
+	    || (flags & (MSG_NBIO | MSG_DONTWAIT)) != 0
 	    ) {
 		non_blocking = 1;
 	}
Index: head/sys/ofed/drivers/infiniband/ulp/sdp/sdp_main.c
===================================================================
--- head/sys/ofed/drivers/infiniband/ulp/sdp/sdp_main.c
+++ head/sys/ofed/drivers/infiniband/ulp/sdp/sdp_main.c
@@ -1124,7 +1124,8 @@
 		}
 		if (space < resid &&
 		    (atomic || space < so->so_snd.sb_lowat)) {
-			if ((so->so_state & SS_NBIO) || (flags & MSG_NBIO)) {
+			if ((so->so_state & SS_NBIO) ||
+			    (flags & (MSG_NBIO | MSG_DONTWAIT)) != 0) {
 				SOCKBUF_UNLOCK(&so->so_snd);
 				error = EWOULDBLOCK;
 				goto release;