virtio_blk: remove nents member.

It's simply a flag as to whether we have data now, so make it an
explicit function parameter rather than a member of struct
virtblk_req.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Reviewed-by: Asias He <asias@redhat.com>

drivers/block/virtio_blk.c

@@ -62,7 +62,6 @@ struct virtblk_req
 	struct virtio_blk *vblk;
 	int flags;
 	u8 status;
-	int nents;
 	struct scatterlist sg[];
 };
 
@@ -104,7 +103,7 @@ static inline struct virtblk_req *virtblk_alloc_req(struct virtio_blk *vblk,
 static int __virtblk_add_req(struct virtqueue *vq,
 			     struct virtblk_req *vbr,
 			     struct scatterlist *data_sg,
-			     unsigned data_nents)
+			     bool have_data)
 {
 	struct scatterlist hdr, status, cmd, sense, inhdr, *sgs[6];
 	unsigned int num_out = 0, num_in = 0;
@@ -124,7 +123,7 @@ static int __virtblk_add_req(struct virtqueue *vq,
 		sgs[num_out++] = &cmd;
 	}
 
-	if (data_nents) {
+	if (have_data) {
 		if (vbr->out_hdr.type & VIRTIO_BLK_T_OUT)
 			sgs[num_out++] = data_sg;
 		else
@@ -144,15 +143,15 @@ static int __virtblk_add_req(struct virtqueue *vq,
 	return virtqueue_add_sgs(vq, sgs, num_out, num_in, vbr, GFP_ATOMIC);
 }
 
-static void virtblk_add_req(struct virtblk_req *vbr)
+static void virtblk_add_req(struct virtblk_req *vbr, bool have_data)
 {
 	struct virtio_blk *vblk = vbr->vblk;
 	DEFINE_WAIT(wait);
 	int ret;
 
 	spin_lock_irq(vblk->disk->queue->queue_lock);
 	while (unlikely((ret = __virtblk_add_req(vblk->vq, vbr, vbr->sg,
-						 vbr->nents)) < 0)) {
+						 have_data)) < 0)) {
 		prepare_to_wait_exclusive(&vblk->queue_wait, &wait,
 					  TASK_UNINTERRUPTIBLE);
 
@@ -173,30 +172,31 @@ static void virtblk_bio_send_flush(struct virtblk_req *vbr)
 	vbr->out_hdr.type = VIRTIO_BLK_T_FLUSH;
 	vbr->out_hdr.sector = 0;
 	vbr->out_hdr.ioprio = 0;
-	vbr->nents = 0;
 
-	virtblk_add_req(vbr);
+	virtblk_add_req(vbr, false);
 }
 
 static void virtblk_bio_send_data(struct virtblk_req *vbr)
 {
 	struct virtio_blk *vblk = vbr->vblk;
 	struct bio *bio = vbr->bio;
+	bool have_data;
 
 	vbr->flags &= ~VBLK_IS_FLUSH;
 	vbr->out_hdr.type = 0;
 	vbr->out_hdr.sector = bio->bi_sector;
 	vbr->out_hdr.ioprio = bio_prio(bio);
 
-	vbr->nents = blk_bio_map_sg(vblk->disk->queue, bio, vbr->sg);
-	if (vbr->nents) {
+	if (blk_bio_map_sg(vblk->disk->queue, bio, vbr->sg)) {
+		have_data = true;
 		if (bio->bi_rw & REQ_WRITE)
 			vbr->out_hdr.type |= VIRTIO_BLK_T_OUT;
 		else
 			vbr->out_hdr.type |= VIRTIO_BLK_T_IN;
-	}
+	} else
+		have_data = false;
 
-	virtblk_add_req(vbr);
+	virtblk_add_req(vbr, have_data);
 }
 
 static void virtblk_bio_send_data_work(struct work_struct *work)