xen/blkback: Fix the WRITE_BARRIER

The WRITE_BARRIER was missing the REQ_WRITE option. This
was causing the blktap to die.
Signed-off-by: Tom Goetz <tom.goetz@virtualcomputer.com>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>

drivers/xen/blkback/blkback.c

@@ -47,6 +47,8 @@
 #include <asm/xen/hypercall.h>
 #include "common.h"
 
+#define WRITE_BARRIER	(REQ_WRITE | REQ_FLUSH | REQ_FUA)
+
 /*
  * These are rather arbitrary. They are fairly large because adjacent requests
  * pulled from a communication ring are quite likely to end up being part of
@@ -420,7 +422,7 @@ static void dispatch_rw_block_io(blkif_t *blkif,
 		operation = WRITE;
 		break;
 	case BLKIF_OP_WRITE_BARRIER:
-		operation = REQ_FLUSH | REQ_FUA;
+		operation = WRITE_BARRIER;
 		break;
 	default:
 		operation = 0; /* make gcc happy */
@@ -429,7 +431,7 @@ static void dispatch_rw_block_io(blkif_t *blkif,
 
 	/* Check that number of segments is sane. */
 	nseg = req->nr_segments;
-	if (unlikely(nseg == 0 && operation != (REQ_FLUSH | REQ_FUA)) ||
+	if (unlikely(nseg == 0 && operation != WRITE_BARRIER) ||
 	    unlikely(nseg > BLKIF_MAX_SEGMENTS_PER_REQUEST)) {
 		DPRINTK("Bad number of segments in request (%d)\n", nseg);
 		goto fail_response;
@@ -537,7 +539,7 @@ static void dispatch_rw_block_io(blkif_t *blkif,
 	}
 
 	if (!bio) {
-		BUG_ON(operation != (REQ_FLUSH | REQ_FUA));
+		BUG_ON(operation != WRITE_BARRIER);
 		bio = bio_alloc(GFP_KERNEL, 0);
 		if (unlikely(bio == NULL))
 			goto fail_put_bio;
@@ -552,7 +554,7 @@ static void dispatch_rw_block_io(blkif_t *blkif,
 
 	if (operation == READ)
 		blkif->st_rd_sect += preq.nr_sects;
-	else if (operation == WRITE || operation == (REQ_FLUSH | REQ_FUA))
+	else if (operation == WRITE || operation == WRITE_BARRIER)
 		blkif->st_wr_sect += preq.nr_sects;
 
 	return;