Index: sys/sys/vnode.h
===================================================================
--- sys/sys/vnode.h	(revision 229701)
+++ sys/sys/vnode.h	(working copy)
@@ -695,6 +695,9 @@ int	vop_stdpathconf(struct vop_pathconf_args *);
 int	vop_stdpoll(struct vop_poll_args *);
 int	vop_stdvptocnp(struct vop_vptocnp_args *ap);
 int	vop_stdvptofh(struct vop_vptofh_args *ap);
+int	vop_stdunpbind(struct vop_unpbind_args *ap);
+int	vop_stdunpconnect(struct vop_unpconnect_args *ap);
+int	vop_stdunpdetach(struct vop_unpdetach_args *ap);
 int	vop_eopnotsupp(struct vop_generic_args *ap);
 int	vop_ebadf(struct vop_generic_args *ap);
 int	vop_einval(struct vop_generic_args *ap);
Index: sys/kern/uipc_usrreq.c
===================================================================
--- sys/kern/uipc_usrreq.c	(revision 229701)
+++ sys/kern/uipc_usrreq.c	(working copy)
@@ -542,7 +542,7 @@ restart:
 
 	UNP_LINK_WLOCK();
 	UNP_PCB_LOCK(unp);
-	vp->v_socket = unp->unp_socket;
+	VOP_UNPBIND(vp, unp->unp_socket);
 	unp->unp_vnode = vp;
 	unp->unp_addr = soun;
 	unp->unp_flags &= ~UNP_BINDING;
@@ -638,7 +638,7 @@ uipc_detach(struct socket *so)
 	 * XXXRW: Should assert vp->v_socket == so.
 	 */
 	if ((vp = unp->unp_vnode) != NULL) {
-		unp->unp_vnode->v_socket = NULL;
+		VOP_UNPDETACH(vp);
 		unp->unp_vnode = NULL;
 	}
 	unp2 = unp->unp_conn;
@@ -1308,7 +1308,7 @@ unp_connect(struct socket *so, struct sockaddr *na
 	 * and to protect simultaneous locking of multiple pcbs.
 	 */
 	UNP_LINK_WLOCK();
-	so2 = vp->v_socket;
+	VOP_UNPCONNECT(vp, &so2);
 	if (so2 == NULL) {
 		error = ECONNREFUSED;
 		goto bad2;
Index: sys/kern/vfs_default.c
===================================================================
--- sys/kern/vfs_default.c	(revision 229701)
+++ sys/kern/vfs_default.c	(working copy)
@@ -123,6 +123,9 @@ struct vop_vector default_vnodeops = {
 	.vop_unlock =		vop_stdunlock,
 	.vop_vptocnp =		vop_stdvptocnp,
 	.vop_vptofh =		vop_stdvptofh,
+	.vop_unpbind =		vop_stdunpbind,
+	.vop_unpconnect =	vop_stdunpconnect,
+	.vop_unpdetach =	vop_stdunpdetach,
 };
 
 /*
@@ -1037,6 +1040,39 @@ vop_stdadvise(struct vop_advise_args *ap)
 	return (error);
 }
 
+int
+vop_stdunpbind(struct vop_unpbind_args *ap)
+{
+	struct vnode *vp;
+
+	vp = ap->a_vp;
+
+	vp->v_socket = ap->a_socket;
+	return (0);
+}
+
+int
+vop_stdunpconnect(struct vop_unpconnect_args *ap)
+{
+	struct vnode *vp;
+
+	vp = ap->a_vp;
+
+	*ap->a_socket = vp->v_socket;
+	return (0);
+}
+
+int
+vop_stdunpdetach(struct vop_unpdetach_args *ap)
+{
+	struct vnode *vp;
+
+	vp = ap->a_vp;
+
+	vp->v_socket = NULL;
+	return (0);
+}
+
 /*
  * vfs default ops
  * used to fill the vfs function table to get reasonable default return values.
Index: sys/kern/vnode_if.src
===================================================================
--- sys/kern/vnode_if.src	(revision 229701)
+++ sys/kern/vnode_if.src	(working copy)
@@ -639,3 +639,23 @@ vop_advise {
 	IN off_t end;
 	IN int advice;
 };
+
+%% unpbind	vp	E E E
+
+vop_unpbind {
+	IN struct vnode *vp;
+	IN struct socket *socket;
+};
+
+%% unpconnect	vp	E E E
+
+vop_unpconnect {
+	IN struct vnode *vp;
+	OUT struct socket **socket;
+};
+
+%% unpdetach	vp	E E E
+
+vop_unpdetach {
+	IN struct vnode *vp;
+};
Index: sys/fs/nullfs/null.h
===================================================================
--- sys/fs/nullfs/null.h	(revision 229701)
+++ sys/fs/nullfs/null.h	(working copy)
@@ -37,8 +37,15 @@
 struct null_mount {
 	struct mount	*nullm_vfs;
 	struct vnode	*nullm_rootvp;	/* Reference to root null_node */
+	uint64_t	nullm_flags;	/* nullfs options specific for mount */
 };
 
+/*
+ * Flags stored in nullm_flags.
+ */
+#define	NULLMNT_SOBYPASS	0x00000001	/* Bypass unix socket operations
+						   to lower vnode */
+
 #ifdef _KERNEL
 /*
  * A cache of vnode references
@@ -47,8 +54,16 @@ struct null_node {
 	LIST_ENTRY(null_node)	null_hash;	/* Hash list */
 	struct vnode	        *null_lowervp;	/* VREFed once */
 	struct vnode		*null_vnode;	/* Back pointer */
+	u_int			null_flags;	/* Flags */
 };
 
+/*
+ * Flags stored in null_flags.
+ */
+
+#define	NULL_SOBYPASS	0x00000001	/* Bypass unix socket operations
+					   to lower vnode */
+
 #define	MOUNTTONULLMOUNT(mp) ((struct null_mount *)((mp)->mnt_data))
 #define	VTONULL(vp) ((struct null_node *)(vp)->v_data)
 #define	NULLTOV(xp) ((xp)->null_vnode)
Index: sys/fs/nullfs/null_vnops.c
===================================================================
--- sys/fs/nullfs/null_vnops.c	(revision 229701)
+++ sys/fs/nullfs/null_vnops.c	(working copy)
@@ -812,6 +812,52 @@ null_vptocnp(struct vop_vptocnp_args *ap)
 	return (error);
 }
 
+static int
+null_unpbind(struct vop_unpbind_args *ap)
+{
+	struct vnode *vp;
+	struct null_node *xp;
+	struct null_mount *xmp;
+
+	vp = ap->a_vp;
+	xp = VTONULL(vp);
+	xmp = MOUNTTONULLMOUNT(vp->v_mount);
+	if (xmp->nullm_flags & NULLMNT_SOBYPASS) {
+		xp->null_flags |= NULL_SOBYPASS;
+		return (null_bypass((struct vop_generic_args *)ap));
+	} else {
+		return (vop_stdunpbind(ap));
+	}
+}
+
+static int
+null_unpconnect(struct vop_unpconnect_args *ap)
+{
+	struct vnode *vp;
+	struct null_mount *xmp;
+
+	vp = ap->a_vp;
+	xmp = MOUNTTONULLMOUNT(vp->v_mount);
+	if (xmp->nullm_flags & NULLMNT_SOBYPASS)
+		return (null_bypass((struct vop_generic_args *)ap));
+	else
+		return (vop_stdunpconnect(ap));
+}
+
+static int
+null_unpdetach(struct vop_unpdetach_args *ap)
+{
+	struct vnode *vp;
+	struct null_node *xp;
+
+	vp = ap->a_vp;
+	xp = VTONULL(vp);
+	if (xp->null_flags & NULL_SOBYPASS)
+		return (null_bypass((struct vop_generic_args *)ap));
+	else
+		return (vop_stdunpdetach(ap));
+}
+
 /*
  * Global vfs data structures
  */
@@ -837,4 +883,7 @@ struct vop_vector null_vnodeops = {
 	.vop_unlock =		null_unlock,
 	.vop_vptocnp =		null_vptocnp,
 	.vop_vptofh =		null_vptofh,
+	.vop_unpbind =		null_unpbind,
+	.vop_unpconnect =	null_unpconnect,
+	.vop_unpdetach =	null_unpdetach,
 };
Index: sys/fs/nullfs/null_subr.c
===================================================================
--- sys/fs/nullfs/null_subr.c	(revision 229701)
+++ sys/fs/nullfs/null_subr.c	(working copy)
@@ -235,6 +235,7 @@ null_nodeget(mp, lowervp, vpp)
 
 	xp->null_vnode = vp;
 	xp->null_lowervp = lowervp;
+	xp->null_flags = 0;
 	vp->v_type = lowervp->v_type;
 	vp->v_data = xp;
 	vp->v_vnlock = lowervp->v_vnlock;
Index: sys/fs/nullfs/null_vfsops.c
===================================================================
--- sys/fs/nullfs/null_vfsops.c	(revision 229701)
+++ sys/fs/nullfs/null_vfsops.c	(working copy)
@@ -84,16 +84,26 @@ nullfs_mount(struct mount *mp)
 	if (mp->mnt_flag & MNT_ROOTFS)
 		return (EOPNOTSUPP);
 	/*
-	 * Update is a no-op
+	 * Update is supported only for some options.
 	 */
 	if (mp->mnt_flag & MNT_UPDATE) {
-		/*
-		 * Only support update mounts for NFS export.
-		 */
+		error = EOPNOTSUPP;
+		xmp = MOUNTTONULLMOUNT(mp);
+		if (vfs_flagopt(mp->mnt_optnew, "sobypass", NULL, 0)) {
+			MNT_ILOCK(mp);
+			xmp->nullm_flags |= NULLMNT_SOBYPASS;
+			MNT_IUNLOCK(mp);
+			error = 0;
+		}
+		if (vfs_flagopt(mp->mnt_optnew, "nosobypass", NULL, 0)) {
+			MNT_ILOCK(mp);
+			xmp->nullm_flags &= ~NULLMNT_SOBYPASS;
+			MNT_IUNLOCK(mp);
+			error = 0;
+		}
 		if (vfs_flagopt(mp->mnt_optnew, "export", NULL, 0))
-			return (0);
-		else
-			return (EOPNOTSUPP);
+			error = 0;
+		return (error);
 	}
 
 	/*
@@ -182,6 +192,11 @@ nullfs_mount(struct mount *mp)
 	MNT_ILOCK(mp);
 	mp->mnt_kern_flag |= lowerrootvp->v_mount->mnt_kern_flag & MNTK_MPSAFE;
 	MNT_IUNLOCK(mp);
+
+	xmp->nullm_flags = 0;
+	vfs_flagopt(mp->mnt_optnew, "sobypass", &xmp->nullm_flags,
+	    NULLMNT_SOBYPASS);
+
 	mp->mnt_data =  xmp;
 	vfs_getnewfsid(mp);
 
Index: sbin/mount_nullfs/mount_nullfs.c
===================================================================
--- sbin/mount_nullfs/mount_nullfs.c	(revision 229701)
+++ sbin/mount_nullfs/mount_nullfs.c	(working copy)
@@ -57,27 +57,36 @@ static const char rcsid[] =
 
 #include "mntopts.h"
 
+#define NULLOPT_SOBYPASS	0x00000001
+#define NULLOPT_MASK		(NULLOPT_SOBYPASS)
+
 static struct mntopt mopts[] = {
 	MOPT_STDOPTS,
+	MOPT_UPDATE,
+	{"sobypass", 0, NULLOPT_SOBYPASS, 1},
 	MOPT_END
 };
 
+static char fstype[] = "nullfs";
+
 int	subdir(const char *, const char *);
 static void	usage(void) __dead2;
 
 int
 main(int argc, char *argv[])
 {
-	struct iovec iov[6];
-	int ch, mntflags;
+	struct iovec *iov;
+	int ch, iovlen, mntflags, nullflags, negflags;
 	char source[MAXPATHLEN];
 	char target[MAXPATHLEN];
 
-	mntflags = 0;
+	mntflags = nullflags = 0;
+	negflags = NULLOPT_MASK;
 	while ((ch = getopt(argc, argv, "o:")) != -1)
 		switch(ch) {
 		case 'o':
-			getmntopts(optarg, mopts, &mntflags, 0);
+			getmntopts(optarg, mopts, &mntflags, &nullflags);
+			getmntopts(optarg, mopts, &mntflags, &negflags);
 			break;
 		case '?':
 		default:
@@ -97,20 +106,18 @@ main(int argc, char *argv[])
 		errx(EX_USAGE, "%s (%s) and %s are not distinct paths",
 		    argv[0], target, argv[1]);
 
-	iov[0].iov_base = strdup("fstype");
-	iov[0].iov_len = sizeof("fstype");
-	iov[1].iov_base = strdup("nullfs");
-	iov[1].iov_len = strlen(iov[1].iov_base) + 1;
-	iov[2].iov_base = strdup("fspath");
-	iov[2].iov_len = sizeof("fspath");
-	iov[3].iov_base = source;
-	iov[3].iov_len = strlen(source) + 1;
-	iov[4].iov_base = strdup("target");
-	iov[4].iov_len = sizeof("target");
-	iov[5].iov_base = target;
-	iov[5].iov_len = strlen(target) + 1;
-
-	if (nmount(iov, 6, mntflags))
+	iov = NULL;
+	iovlen = 0;
+	build_iovec(&iov, &iovlen, "fstype", fstype, (size_t)-1);
+	build_iovec(&iov, &iovlen, "fspath", source, (size_t)-1);
+	build_iovec(&iov, &iovlen, "target", target, (size_t)-1);
+	if ((nullflags & NULLOPT_SOBYPASS) != 0)
+		build_iovec(&iov, &iovlen, "sobypass", NULL, 0);
+	if ((mntflags & MNT_UPDATE) != 0) {
+		if ((negflags & NULLOPT_SOBYPASS) == 0)
+			build_iovec(&iov, &iovlen, "nosobypass", NULL, 0);
+	}
+	if (nmount(iov, iovlen, mntflags))
 		err(1, NULL);
 	exit(0);
 }
Index: sbin/mount_nullfs/mount_nullfs.8
===================================================================
--- sbin/mount_nullfs/mount_nullfs.8	(revision 229701)
+++ sbin/mount_nullfs/mount_nullfs.8	(working copy)
@@ -79,8 +79,14 @@ Options are specified with a
 flag followed by a comma separated string of options.
 See the
 .Xr mount 8
-man page for possible options and their meanings.
+man page for standard options and their meanings.
+Options specific for
+.Nm :
+.Bl -tag -width sobypass
+.It Cm sobypass
+Bypass unix socket operations to the lower layer.
 .El
+.El
 .Pp
 The null layer has two purposes.
 First, it serves as a demonstration of layering by providing a layer