commit 2af293bca114be0b4660e56320dde7fd4798e14f
Author: Mikolaj Golub <trociny@freebsd.org>
Date:   Sat Feb 18 22:09:38 2012 +0200

    Introduce VOP_UNPBIND(), VOP_UNPCONNECT(), and VOP_UNPDETACH()
    operations for setting and accessing vnode's v_socket field.
    
    The operations are necessary to implement proper unix socket handling
    on layered file systems like nullfs(5).
    
    This change fixes the long standing issue with nullfs(5) being in that
    unix sockets did not work between lower and upper layers: if we bound
    to a socket on the lower layer we could connect only to the lower
    path; if we bound to the upper layer we could connect only to the
    upper path.
    
    The new behavior is one can connect to both the lower and the upper
    paths regardless if we bind to lower or upper fs.
    
    Suggested by:	kib
    Reviewed by:	arch

diff --git a/sys/kern/uipc_usrreq.c b/sys/kern/uipc_usrreq.c
index 54b37ec..5165cf2 100644
--- a/sys/kern/uipc_usrreq.c
+++ b/sys/kern/uipc_usrreq.c
@@ -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;
@@ -1256,17 +1256,15 @@ unp_prepare_reclaim(struct vnode *vp)
 
 	active = 0;
 	UNP_LINK_WLOCK();
-	so = vp->v_socket;
+	VOP_UNPCONNECT(vp, &so);
 	if (so == NULL)
 		goto done;
 	unp = sotounpcb(so);
 	if (unp == NULL)
 		goto done;
 	UNP_PCB_LOCK(unp);
-	if (unp->unp_vnode != NULL) {
-		KASSERT(unp->unp_vnode == vp,
-		    ("unp_prepare_reclaim: vp != unp->unp_vnode"));
-		vp->v_socket = NULL;
+	if (unp->unp_vnode == vp) {
+		VOP_UNPDETACH(vp);
 		unp->unp_vnode = NULL;
 		active = 1;
 	}
@@ -1347,7 +1345,7 @@ unp_connect(struct socket *so, struct sockaddr *nam, struct thread *td)
 	 * 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;
diff --git a/sys/kern/vfs_default.c b/sys/kern/vfs_default.c
index e47498e..3405311 100644
--- a/sys/kern/vfs_default.c
+++ b/sys/kern/vfs_default.c
@@ -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 +1040,30 @@ vop_stdadvise(struct vop_advise_args *ap)
 	return (error);
 }
 
+int
+vop_stdunpbind(struct vop_unpbind_args *ap)
+{
+
+	ap->a_vp->v_socket = ap->a_socket;
+	return (0);
+}
+
+int
+vop_stdunpconnect(struct vop_unpconnect_args *ap)
+{
+
+	*ap->a_socket = ap->a_vp->v_socket;
+	return (0);
+}
+
+int
+vop_stdunpdetach(struct vop_unpdetach_args *ap)
+{
+
+	ap->a_vp->v_socket = NULL;
+	return (0);
+}
+
 /*
  * vfs default ops
  * used to fill the vfs function table to get reasonable default return values.
diff --git a/sys/kern/vnode_if.src b/sys/kern/vnode_if.src
index 5da4c1c..ff8ee8c 100644
--- a/sys/kern/vnode_if.src
+++ b/sys/kern/vnode_if.src
@@ -640,6 +640,26 @@ vop_advise {
 	IN int advice;
 };
 
+%% unpbind	vp	E E E
+
+vop_unpbind {
+	IN struct vnode *vp;
+	IN struct socket *socket;
+};
+
+%% unpconnect	vp	L L L
+
+vop_unpconnect {
+	IN struct vnode *vp;
+	OUT struct socket **socket;
+};
+
+%% unpdetach	vp	= = =
+
+vop_unpdetach {
+	IN struct vnode *vp;
+};
+
 # The VOPs below are spares at the end of the table to allow new VOPs to be
 # added in stable branches without breaking the KBI.  New VOPs in HEAD should
 # be added above these spares.  When merging a new VOP to a stable branch,
diff --git a/sys/sys/vnode.h b/sys/sys/vnode.h
index 4fd5a28..e0da44e 100644
--- a/sys/sys/vnode.h
+++ b/sys/sys/vnode.h
@@ -703,6 +703,9 @@ 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);