virtio: de-structify virtio_block status byte

Ron Minnich points out that a struct containing a char is not always
sizeof(char); simplest to remove the structure to avoid confusion.

Cc: "ron minnich" <rminnich@gmail.com>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

Documentation/lguest/lguest.c

@@ -1398,7 +1398,7 @@ static bool service_io(struct device *dev)
 	struct vblk_info *vblk = dev->priv;
 	unsigned int head, out_num, in_num, wlen;
 	int ret;
-	struct virtio_blk_inhdr *in;
+	u8 *in;
 	struct virtio_blk_outhdr *out;
 	struct iovec iov[dev->vq->vring.num];
 	off64_t off;
@@ -1416,7 +1416,7 @@ static bool service_io(struct device *dev)
 		     head, out_num, in_num);
 
 	out = convert(&iov[0], struct virtio_blk_outhdr);
-	in = convert(&iov[out_num+in_num-1], struct virtio_blk_inhdr);
+	in = convert(&iov[out_num+in_num-1], u8);
 	off = out->sector * 512;
 
 	/* The block device implements "barriers", where the Guest indicates
@@ -1430,7 +1430,7 @@ static bool service_io(struct device *dev)
 	 * It'd be nice if we supported eject, for example, but we don't. */
 	if (out->type & VIRTIO_BLK_T_SCSI_CMD) {
 		fprintf(stderr, "Scsi commands unsupported\n");
-		in->status = VIRTIO_BLK_S_UNSUPP;
+		*in = VIRTIO_BLK_S_UNSUPP;
 		wlen = sizeof(*in);
 	} else if (out->type & VIRTIO_BLK_T_OUT) {
 		/* Write */
@@ -1453,7 +1453,7 @@ static bool service_io(struct device *dev)
 			errx(1, "Write past end %llu+%u", off, ret);
 		}
 		wlen = sizeof(*in);
-		in->status = (ret >= 0 ? VIRTIO_BLK_S_OK : VIRTIO_BLK_S_IOERR);
+		*in = (ret >= 0 ? VIRTIO_BLK_S_OK : VIRTIO_BLK_S_IOERR);
 	} else {
 		/* Read */
 
@@ -1466,10 +1466,10 @@ static bool service_io(struct device *dev)
 		verbose("READ from sector %llu: %i\n", out->sector, ret);
 		if (ret >= 0) {
 			wlen = sizeof(*in) + ret;
-			in->status = VIRTIO_BLK_S_OK;
+			*in = VIRTIO_BLK_S_OK;
 		} else {
 			wlen = sizeof(*in);
-			in->status = VIRTIO_BLK_S_IOERR;
+			*in = VIRTIO_BLK_S_IOERR;
 		}
 	}
 

drivers/block/virtio_blk.c

@@ -35,7 +35,7 @@ struct virtblk_req
 	struct list_head list;
 	struct request *req;
 	struct virtio_blk_outhdr out_hdr;
-	struct virtio_blk_inhdr in_hdr;
+	u8 status;
 };
 
 static void blk_done(struct virtqueue *vq)
@@ -48,7 +48,7 @@ static void blk_done(struct virtqueue *vq)
 	spin_lock_irqsave(&vblk->lock, flags);
 	while ((vbr = vblk->vq->vq_ops->get_buf(vblk->vq, &len)) != NULL) {
 		int uptodate;
-		switch (vbr->in_hdr.status) {
+		switch (vbr->status) {
 		case VIRTIO_BLK_S_OK:
 			uptodate = 1;
 			break;
@@ -101,7 +101,7 @@ static bool do_req(struct request_queue *q, struct virtio_blk *vblk,
 	sg_init_table(vblk->sg, VIRTIO_MAX_SG);
 	sg_set_buf(&vblk->sg[0], &vbr->out_hdr, sizeof(vbr->out_hdr));
 	num = blk_rq_map_sg(q, vbr->req, vblk->sg+1);
-	sg_set_buf(&vblk->sg[num+1], &vbr->in_hdr, sizeof(vbr->in_hdr));
+	sg_set_buf(&vblk->sg[num+1], &vbr->status, sizeof(vbr->status));
 
 	if (rq_data_dir(vbr->req) == WRITE) {
 		vbr->out_hdr.type |= VIRTIO_BLK_T_OUT;

include/linux/virtio_blk.h

@@ -41,13 +41,8 @@ struct virtio_blk_outhdr
 	__u64 sector;
 };
 
+/* And this is the final byte of the write scatter-gather list. */
 #define VIRTIO_BLK_S_OK		0
 #define VIRTIO_BLK_S_IOERR	1
 #define VIRTIO_BLK_S_UNSUPP	2
-
-/* This is the first element of the write scatter-gather list */
-struct virtio_blk_inhdr
-{
-	unsigned char status;
-};
 #endif /* _LINUX_VIRTIO_BLK_H */