--- //depot/projects/smpng/sys/net/if.c	2009/12/16 22:22:28
+++ //depot/user/jhb/socket/net/if.c	2009/12/21 22:08:44
@@ -2095,6 +2095,14 @@
 			return (EINVAL);
 		if (ifunit(new_name) != NULL)
 			return (EEXIST);
+
+		/*
+		 * XXX: Locking.  Nothing else seems to lock if_flags,
+		 * and there are numerous other races with the
+		 * ifunit() checks not being atomic with namespace
+		 * changes (renames, vmoves, if_attach, etc).
+		 */
+		ifp->if_flags |= IFF_RENAMING;
 		
 		/* Announce the departure of the interface. */
 		rt_ifannouncemsg(ifp, IFAN_DEPARTURE);
@@ -2129,6 +2137,8 @@
 		EVENTHANDLER_INVOKE(ifnet_arrival_event, ifp);
 		/* Announce the return of the interface. */
 		rt_ifannouncemsg(ifp, IFAN_ARRIVAL);
+
+		ifp->if_flags &= ~IFF_RENAMING;
 		break;
 
 #ifdef VIMAGE
--- //depot/projects/smpng/sys/net/if.h	2009/12/16 22:22:28
+++ //depot/user/jhb/socket/net/if.h	2009/12/21 20:06:35
@@ -150,6 +150,7 @@
 #define	IFF_MONITOR	0x40000		/* (n) user-requested monitor mode */
 #define	IFF_STATICARP	0x80000		/* (n) static ARP */
 #define	IFF_DYING	0x200000	/* (n) interface is winding down */
+#define	IFF_RENAMING	0x400000	/* (n) interface is being renamed */
 
 /*
  * Old names for driver flags so that user space tools can continue to use
--- //depot/projects/smpng/sys/net/if_vlan.c	2009/09/10 18:23:03
+++ //depot/user/jhb/socket/net/if_vlan.c	2009/12/21 22:08:44
@@ -466,7 +466,8 @@
  * A handler for network interface departure events.
  * Track departure of trunks here so that we don't access invalid
  * pointers or whatever if a trunk is ripped from under us, e.g.,
- * by ejecting its hot-plug card.
+ * by ejecting its hot-plug card.  However, if an ifnet is simply
+ * being renamed, then there's no need to tear down the state.
  */
 static void
 vlan_ifdetach(void *arg __unused, struct ifnet *ifp)
@@ -481,6 +482,10 @@
 	if (ifp->if_vlantrunk == NULL)
 		return;
 
+	/* If the ifnet is just being renamed, don't do anything. */
+	if (ifp->if_flags & IFF_RENAMING)
+		return;
+
 	VLAN_LOCK();
 	/*
 	 * OK, it's a trunk.  Loop over and detach all vlan's on it.