unix: retire LOCAL_CONNWAIT

This socket option was added in 6a2989fd54a9 together with LOCAL_CREDS.
Both options originate from NetBSD.  The LOCAL_CREDS seems to be used by
some software and is covered by our test suite.

The main problem with LOCAL_CONNWAIT is that it doesn't work as
documented. A basic test shows that connect(2) indeed blocks, but
accept(2) on the other side does not wake it up.  Indeed, I don't see what
code in the accept(2) path would go into the peer socket of a unix/stream
listener's child and would make wakeup(&so->so_timeo).  I tried the test
even on a FreeBSD 6.4-RELEASE and it produced the same results as on
CURRENT.

The other thing that puzzles me is why that option would be useful even if
it worked? Because on unix/stream you can send(2) immediately after
connect(2) and that would put data on the peer receive buffer even before
listener had done accept(2). In other words, one side can do connect(2)
then send(2), only after the remote side would make accept(2) and the
remote would see the data sent before the accept(2).  Again this
undocumented feature of unix(4) is present on all versions from FreeBSD 6
to CURRENT.

Reviewed by:		markj
Differential Revision:	https://reviews.freebsd.org/D43708

4 files changed, 6 insertions, 37 deletions

diff --git a/share/man/man4/unix.4 b/share/man/man4/unix.4
index 24069ae4663c..5ac9ccd5514f 100644
--- a/share/man/man4/unix.4
+++ b/share/man/man4/unix.4
@@ -25,7 +25,7 @@
 .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 .\" SUCH DAMAGE.
 .\"
-.Dd June 24, 2022
+.Dd February 1, 2022
 .Dt UNIX 4
 .Os
 .Sh NAME
@@ -332,14 +332,6 @@ The
 and
 .Dv LOCAL_CREDS_PERSISTENT
 options are mutually exclusive.
-.It Dv LOCAL_CONNWAIT
-Used with
-.Dv SOCK_STREAM
-sockets, this option causes the
-.Xr connect 2
-function to block until
-.Xr accept 2
-has been called on the listening socket.
 .It Dv LOCAL_PEERCRED
 Requested via
 .Xr getsockopt 2
diff --git a/sys/kern/uipc_usrreq.c b/sys/kern/uipc_usrreq.c
index 80458cd6a4fe..db226a16674e 100644
--- a/sys/kern/uipc_usrreq.c
+++ b/sys/kern/uipc_usrreq.c
@@ -291,8 +291,7 @@ static int	unp_connect(struct socket *, struct sockaddr *,
 		    struct thread *);
 static int	unp_connectat(int, struct socket *, struct sockaddr *,
 		    struct thread *, bool);
-typedef enum { PRU_CONNECT, PRU_CONNECT2 } conn2_how;
-static void	unp_connect2(struct socket *so, struct socket *so2, conn2_how);
+static void	unp_connect2(struct socket *so, struct socket *so2);
 static void	unp_disconnect(struct unpcb *unp, struct unpcb *unp2);
 static void	unp_dispose(struct socket *so);
 static void	unp_shutdown(struct unpcb *);
@@ -704,7 +703,7 @@ uipc_connect2(struct socket *so1, struct socket *so2)
 	unp2 = so2->so_pcb;
 	KASSERT(unp2 != NULL, ("uipc_connect2: unp2 == NULL"));
 	unp_pcb_lock_pair(unp, unp2);
-	unp_connect2(so1, so2, PRU_CONNECT2);
+	unp_connect2(so1, so2);
 	unp_pcb_unlock_pair(unp, unp2);
 
 	return (0);
@@ -1784,12 +1783,6 @@ uipc_ctloutput(struct socket *so, struct sockopt *sopt)
 			error = sooptcopyout(sopt, &optval, sizeof(optval));
 			break;
 
-		case LOCAL_CONNWAIT:
-			/* Unlocked read. */
-			optval = unp->unp_flags & UNP_CONNWAIT ? 1 : 0;
-			error = sooptcopyout(sopt, &optval, sizeof(optval));
-			break;
-
 		default:
 			error = EOPNOTSUPP;
 			break;
@@ -1800,7 +1793,6 @@ uipc_ctloutput(struct socket *so, struct sockopt *sopt)
 		switch (sopt->sopt_name) {
 		case LOCAL_CREDS:
 		case LOCAL_CREDS_PERSISTENT:
-		case LOCAL_CONNWAIT:
 			error = sooptcopyin(sopt, &optval, sizeof(optval),
 					    sizeof(optval));
 			if (error)
@@ -1829,10 +1821,6 @@ uipc_ctloutput(struct socket *so, struct sockopt *sopt)
 				OPTSET(UNP_WANTCRED_ALWAYS, UNP_WANTCRED_ONESHOT);
 				break;
 
-			case LOCAL_CONNWAIT:
-				OPTSET(UNP_CONNWAIT, 0);
-				break;
-
 			default:
 				break;
 			}
@@ -2006,7 +1994,7 @@ unp_connectat(int fd, struct socket *so, struct sockaddr *nam,
 	KASSERT(unp2 != NULL && so2 != NULL && unp2->unp_socket == so2 &&
 	    sotounpcb(so2) == unp2,
 	    ("%s: unp2 %p so2 %p", __func__, unp2, so2));
-	unp_connect2(so, so2, PRU_CONNECT);
+	unp_connect2(so, so2);
 	KASSERT((unp->unp_flags & UNP_CONNECTING) != 0,
 	    ("%s: unp %p has UNP_CONNECTING clear", __func__, unp));
 	unp->unp_flags &= ~UNP_CONNECTING;
@@ -2057,7 +2045,7 @@ unp_copy_peercred(struct thread *td, struct unpcb *client_unp,
 }
 
 static void
-unp_connect2(struct socket *so, struct socket *so2, conn2_how req)
+unp_connect2(struct socket *so, struct socket *so2)
 {
 	struct unpcb *unp;
 	struct unpcb *unp2;
@@ -2089,11 +2077,7 @@ unp_connect2(struct socket *so, struct socket *so2, conn2_how req)
 		KASSERT(unp2->unp_conn == NULL,
 		    ("%s: socket %p is already connected", __func__, unp2));
 		unp2->unp_conn = unp;
-		if (req == PRU_CONNECT &&
-		    ((unp->unp_flags | unp2->unp_flags) & UNP_CONNWAIT))
-			soisconnecting(so);
-		else
-			soisconnected(so);
+		soisconnected(so);
 		soisconnected(so2);
 		break;
 
@@ -3493,10 +3477,6 @@ db_print_unpflags(int unp_flags)
 		db_printf("%sUNP_WANTCRED_ONESHOT", comma ? ", " : "");
 		comma = 1;
 	}
-	if (unp_flags & UNP_CONNWAIT) {
-		db_printf("%sUNP_CONNWAIT", comma ? ", " : "");
-		comma = 1;
-	}
 	if (unp_flags & UNP_CONNECTING) {
 		db_printf("%sUNP_CONNECTING", comma ? ", " : "");
 		comma = 1;
diff --git a/sys/sys/un.h b/sys/sys/un.h
index 640bd254d579..41bde1701900 100644
--- a/sys/sys/un.h
+++ b/sys/sys/un.h
@@ -65,7 +65,6 @@ struct sockaddr_un {
 #define	LOCAL_PEERCRED		1	/* retrieve peer credentials */
 #define	LOCAL_CREDS		2	/* pass credentials to receiver */
 #define	LOCAL_CREDS_PERSISTENT	3	/* pass credentials to receiver */
-#define	LOCAL_CONNWAIT		4	/* connects block until accepted */
 
 /* Start of reserved space for third-party socket options. */
 #define	LOCAL_VENDOR		SO_VENDOR
diff --git a/sys/sys/unpcb.h b/sys/sys/unpcb.h
index fe701d5d38b1..d22662fe83e5 100644
--- a/sys/sys/unpcb.h
+++ b/sys/sys/unpcb.h
@@ -107,8 +107,6 @@ struct unpcb {
 #define	UNP_HAVEPC			0x001
 #define	UNP_WANTCRED_ALWAYS		0x002	/* credentials wanted always */
 #define	UNP_WANTCRED_ONESHOT		0x004	/* credentials wanted once */
-#define	UNP_CONNWAIT			0x008	/* connect blocks until accepted */
-
 #define	UNP_WANTCRED_MASK	(UNP_WANTCRED_ONESHOT | UNP_WANTCRED_ALWAYS)
 
 /*