Index: geom/geom_io.c
===================================================================
--- geom/geom_io.c	(revision 189933)
+++ geom/geom_io.c	(working copy)
@@ -273,6 +273,10 @@
 	cp = bp->bio_from;
 	pp = bp->bio_to;
 
+	/* Proxies are transparent, errors are caught by regular checks. */
+	if (cp->geom->flags & G_GEOM_PROXY)
+		return (0);
+
 	/* Fail if access counters dont allow the operation */
 	switch(bp->bio_cmd) {
 	case BIO_READ:
@@ -343,6 +347,9 @@
 	bp->_bio_cflags = bp->bio_cflags;
 #endif
 
+	if (pp->proxy_provider != NULL && cp != pp->proxy_consumer)
+		pp = pp->proxy_provider;
+
 	if (bp->bio_cmd & (BIO_READ|BIO_WRITE|BIO_GETATTR)) {
 		KASSERT(bp->bio_data != NULL,
 		    ("NULL bp->data in g_io_request(cmd=%hhu)", bp->bio_cmd));
Index: geom/geom_subr.c
===================================================================
--- geom/geom_subr.c	(revision 189933)
+++ geom/geom_subr.c	(working copy)
@@ -365,6 +365,8 @@
 	g_cancel_event(gp);
 	LIST_REMOVE(gp, geom);
 	TAILQ_REMOVE(&geoms, gp, geoms);
+	if (gp->flags & G_GEOM_PROXY)
+		printf("g_destroy_geom(): destroying proxy %s", gp->name);
 	g_free(gp->name);
 	g_free(gp);
 }
@@ -380,6 +382,11 @@
 	g_topology_assert();
 	G_VALID_GEOM(gp);
 	g_trace(G_T_TOPOLOGY, "g_wither_geom(%p(%s))", gp, gp->name);
+	if (gp->flags & G_GEOM_PROXY) {
+		pp = LIST_FIRST(&gp->consumer)->provider;
+		pp->proxy_provider = NULL;
+		pp->proxy_consumer = NULL;
+	}
 	if (!(gp->flags & G_GEOM_WITHER)) {
 		gp->flags |= G_GEOM_WITHER;
 		LIST_FOREACH(pp, &gp->provider, provider)
@@ -581,7 +588,8 @@
 	pp->stat = devstat_new_entry(pp, -1, 0, DEVSTAT_ALL_SUPPORTED,
 	    DEVSTAT_TYPE_DIRECT, DEVSTAT_PRIORITY_MAX);
 	LIST_INSERT_HEAD(&gp->provider, pp, provider);
-	g_post_event(g_new_provider_event, pp, M_WAITOK, pp, gp, NULL);
+	if (!(gp->flags & G_GEOM_PROXY))
+		g_post_event(g_new_provider_event, pp, M_WAITOK, pp, gp, NULL);
 	return (pp);
 }
 
@@ -721,6 +729,20 @@
 	return (error);
 }
 
+int
+g_attach_proxy(struct g_consumer *cp, struct g_provider *pp,
+    struct g_provider *newpp)
+{
+	int error;
+
+	error = g_attach(cp, pp);
+	if (!error) {
+		pp->proxy_provider = newpp;
+		pp->proxy_consumer = cp;
+	}
+	return (error);
+}
+
 void
 g_detach(struct g_consumer *cp)
 {
Index: geom/geom.h
===================================================================
--- geom/geom.h	(revision 189933)
+++ geom/geom.h	(working copy)
@@ -134,6 +134,7 @@
 	void			*softc;
 	unsigned		flags;
 #define	G_GEOM_WITHER		1
+#define	G_GEOM_PROXY		2
 };
 
 /*
@@ -190,6 +191,9 @@
 #define G_PF_WITHER		0x2
 #define G_PF_ORPHAN		0x4
 
+	struct g_provider	*proxy_provider;
+	struct g_consumer	*proxy_consumer;
+
 	/* Two fields for the implementing class to use */
 	void			*private;
 	u_int			index;
@@ -219,6 +223,8 @@
 /* geom_subr.c */
 int g_access(struct g_consumer *cp, int nread, int nwrite, int nexcl);
 int g_attach(struct g_consumer *cp, struct g_provider *pp);
+int g_attach_proxy(struct g_consumer *cp, struct g_provider *pp,
+    struct g_provider *newpp);
 void g_destroy_consumer(struct g_consumer *cp);
 void g_destroy_geom(struct g_geom *pp);
 void g_destroy_provider(struct g_provider *pp);