diff --git a/sys/geom/geom.h b/sys/geom/geom.h
index 5b5562435d62..4d7c5b81497d 100644
--- a/sys/geom/geom.h
+++ b/sys/geom/geom.h
@@ -268,6 +268,7 @@ struct bio * g_duplicate_bio(struct bio *);
 void g_destroy_bio(struct bio *);
 void g_io_deliver(struct bio *bp, int error);
 int g_io_getattr(const char *attr, struct g_consumer *cp, int *len, void *ptr);
+int g_io_flush(struct g_consumer *cp);
 void g_io_request(struct bio *bp, struct g_consumer *cp);
 struct bio *g_new_bio(void);
 struct bio *g_alloc_bio(void);
diff --git a/sys/geom/geom_io.c b/sys/geom/geom_io.c
index c95dbf82aad6..18cedcd38fd5 100644
--- a/sys/geom/geom_io.c
+++ b/sys/geom/geom_io.c
@@ -244,6 +244,26 @@ g_io_getattr(const char *attr, struct g_consumer *cp, int *len, void *ptr)
 	return (error);
 }
 
+int
+g_io_flush(struct g_consumer *cp)
+{
+	struct bio *bp;
+	int error;
+
+	g_trace(G_T_BIO, "bio_flush(%s)", cp->provider->name);
+	bp = g_alloc_bio();
+	bp->bio_cmd = BIO_FLUSH;
+	bp->bio_done = NULL;
+	bp->bio_attribute = NULL;
+	bp->bio_offset = cp->provider->mediasize;
+	bp->bio_length = 0;
+	bp->bio_data = NULL;
+	g_io_request(bp, cp);
+	error = biowait(bp, "gflush");
+	g_destroy_bio(bp);
+	return (error);
+}
+
 static int
 g_io_check(struct bio *bp)
 {
@@ -262,6 +282,7 @@ g_io_check(struct bio *bp)
 		break;
 	case BIO_WRITE:
 	case BIO_DELETE:
+	case BIO_FLUSH:
 		if (cp->acw == 0)
 			return (EPERM);
 		break;
@@ -304,7 +325,6 @@ g_io_request(struct bio *bp, struct g_consumer *cp)
 
 	KASSERT(cp != NULL, ("NULL cp in g_io_request"));
 	KASSERT(bp != NULL, ("NULL bp in g_io_request"));
-	KASSERT(bp->bio_data != NULL, ("NULL bp->data in g_io_request"));
 	pp = cp->provider;
 	KASSERT(pp != NULL, ("consumer not attached in g_io_request"));
 #ifdef DIAGNOSTIC
@@ -323,6 +343,10 @@ g_io_request(struct bio *bp, struct g_consumer *cp)
 	bp->_bio_cflags = bp->bio_cflags;
 #endif
 
+	if (bp->bio_cmd & (BIO_READ|BIO_WRITE|BIO_DELETE|BIO_GETATTR)) {
+		KASSERT(bp->bio_data != NULL,
+		    ("NULL bp->data in g_io_request"));
+	}
 	if (bp->bio_cmd & (BIO_READ|BIO_WRITE|BIO_DELETE)) {
 		KASSERT(bp->bio_offset % cp->provider->sectorsize == 0,
 		    ("wrong offset %jd for sectorsize %u",
@@ -632,6 +656,10 @@ g_print_bio(struct bio *bp)
 		cmd = "GETATTR";
 		printf("%s[%s(attr=%s)]", pname, cmd, bp->bio_attribute);
 		return;
+	case BIO_FLUSH:
+		cmd = "FLUSH";
+		printf("%s[%s]", pname, cmd);
+		return;
 	case BIO_READ:
 		cmd = "READ";
 	case BIO_WRITE:
diff --git a/sys/kern/subr_disk.c b/sys/kern/subr_disk.c
index 56bab3e4da17..c8ed9ced6072 100644
--- a/sys/kern/subr_disk.c
+++ b/sys/kern/subr_disk.c
@@ -43,6 +43,7 @@ disk_err(struct bio *bp, const char *what, int blkdone, int nl)
 	case BIO_WRITE:		printf("cmd=write "); break;
 	case BIO_DELETE:	printf("cmd=delete "); break;
 	case BIO_GETATTR:	printf("cmd=getattr "); break;
+	case BIO_FLUSH:		printf("cmd=flush "); break;
 	default:		printf("cmd=%x ", bp->bio_cmd); break;
 	}
 	sn = bp->bio_pblkno;
diff --git a/sys/sys/bio.h b/sys/sys/bio.h
index 2dbdfb9946ee..36359637daa7 100644
--- a/sys/sys/bio.h
+++ b/sys/sys/bio.h
@@ -93,6 +93,7 @@ struct bio {
 #define BIO_WRITE	0x02
 #define BIO_DELETE	0x04
 #define BIO_GETATTR	0x08
+#define BIO_FLUSH	0x10
 #define BIO_CMD0	0x20	/* Available for local hacks */
 #define BIO_CMD1	0x40	/* Available for local hacks */
 #define BIO_CMD2	0x80	/* Available for local hacks */