virtio-scsi: use virtqueue_add_sgs for command buffers

Using the new virtqueue_add_sgs function lets us simplify the queueing
path.  In particular, all data protected by the tgt_lock is just gone
(multiqueue will find a new use for the lock).

Signed-off-by: Wanlong Gao <gaowanlong@cn.fujitsu.com>
Acked-by: Paolo Bonzini <pbonzini@redhat.com>
Reviewed-by: Asias He <asias@redhat.com>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

drivers/scsi/virtio_scsi.c

@@ -61,11 +61,8 @@ struct virtio_scsi_vq {
 
 /* Per-target queue state */
 struct virtio_scsi_target_state {
-	/* Protects sg.  Lock hierarchy is tgt_lock -> vq_lock.  */
+	/* Never held at the same time as vq_lock.  */
 	spinlock_t tgt_lock;
-
-	/* For sglist construction when adding commands to the virtqueue.  */
-	struct scatterlist sg[];
 };
 
 /* Driver instance state */
@@ -353,75 +350,61 @@ static void virtscsi_event_done(struct virtqueue *vq)
 	spin_unlock_irqrestore(&vscsi->event_vq.vq_lock, flags);
 };
 
-static void virtscsi_map_sgl(struct scatterlist *sg, unsigned int *p_idx,
-			     struct scsi_data_buffer *sdb)
-{
-	struct sg_table *table = &sdb->table;
-	struct scatterlist *sg_elem;
-	unsigned int idx = *p_idx;
-	int i;
-
-	for_each_sg(table->sgl, sg_elem, table->nents, i)
-		sg[idx++] = *sg_elem;
-
-	*p_idx = idx;
-}
-
 /**
- * virtscsi_map_cmd - map a scsi_cmd to a virtqueue scatterlist
- * @vscsi	: virtio_scsi state
+ * virtscsi_add_cmd - add a virtio_scsi_cmd to a virtqueue
+ * @vq		: the struct virtqueue we're talking about
  * @cmd		: command structure
- * @out_num	: number of read-only elements
- * @in_num	: number of write-only elements
  * @req_size	: size of the request buffer
  * @resp_size	: size of the response buffer
- *
- * Called with tgt_lock held.
+ * @gfp	: flags to use for memory allocations
  */
-static void virtscsi_map_cmd(struct virtio_scsi_target_state *tgt,
-			     struct virtio_scsi_cmd *cmd,
-			     unsigned *out_num, unsigned *in_num,
-			     size_t req_size, size_t resp_size)
+static int virtscsi_add_cmd(struct virtqueue *vq,
+			    struct virtio_scsi_cmd *cmd,
+			    size_t req_size, size_t resp_size, gfp_t gfp)
 {
 	struct scsi_cmnd *sc = cmd->sc;
-	struct scatterlist *sg = tgt->sg;
-	unsigned int idx = 0;
+	struct scatterlist *sgs[4], req, resp;
+	struct sg_table *out, *in;
+	unsigned out_num = 0, in_num = 0;
+
+	out = in = NULL;
+
+	if (sc && sc->sc_data_direction != DMA_NONE) {
+		if (sc->sc_data_direction != DMA_FROM_DEVICE)
+			out = &scsi_out(sc)->table;
+		if (sc->sc_data_direction != DMA_TO_DEVICE)
+			in = &scsi_in(sc)->table;
+	}
 
 	/* Request header.  */
-	sg_set_buf(&sg[idx++], &cmd->req, req_size);
+	sg_init_one(&req, &cmd->req, req_size);
+	sgs[out_num++] = &req;
 
 	/* Data-out buffer.  */
-	if (sc && sc->sc_data_direction != DMA_FROM_DEVICE)
-		virtscsi_map_sgl(sg, &idx, scsi_out(sc));
-
-	*out_num = idx;
+	if (out)
+		sgs[out_num++] = out->sgl;
 
 	/* Response header.  */
-	sg_set_buf(&sg[idx++], &cmd->resp, resp_size);
+	sg_init_one(&resp, &cmd->resp, resp_size);
+	sgs[out_num + in_num++] = &resp;
 
 	/* Data-in buffer */
-	if (sc && sc->sc_data_direction != DMA_TO_DEVICE)
-		virtscsi_map_sgl(sg, &idx, scsi_in(sc));
+	if (in)
+		sgs[out_num + in_num++] = in->sgl;
 
-	*in_num = idx - *out_num;
+	return virtqueue_add_sgs(vq, sgs, out_num, in_num, cmd, gfp);
 }
 
-static int virtscsi_kick_cmd(struct virtio_scsi_target_state *tgt,
-			     struct virtio_scsi_vq *vq,
+static int virtscsi_kick_cmd(struct virtio_scsi_vq *vq,
 			     struct virtio_scsi_cmd *cmd,
 			     size_t req_size, size_t resp_size, gfp_t gfp)
 {
-	unsigned int out_num, in_num;
 	unsigned long flags;
 	int err;
 	bool needs_kick = false;
 
-	spin_lock_irqsave(&tgt->tgt_lock, flags);
-	virtscsi_map_cmd(tgt, cmd, &out_num, &in_num, req_size, resp_size);
-
-	spin_lock(&vq->vq_lock);
-	err = virtqueue_add_buf(vq->vq, tgt->sg, out_num, in_num, cmd, gfp);
-	spin_unlock(&tgt->tgt_lock);
+	spin_lock_irqsave(&vq->vq_lock, flags);
+	err = virtscsi_add_cmd(vq->vq, cmd, req_size, resp_size, gfp);
 	if (!err)
 		needs_kick = virtqueue_kick_prepare(vq->vq);
 
@@ -435,7 +418,6 @@ static int virtscsi_kick_cmd(struct virtio_scsi_target_state *tgt,
 static int virtscsi_queuecommand(struct Scsi_Host *sh, struct scsi_cmnd *sc)
 {
 	struct virtio_scsi *vscsi = shost_priv(sh);
-	struct virtio_scsi_target_state *tgt = vscsi->tgt[sc->device->id];
 	struct virtio_scsi_cmd *cmd;
 	int ret;
 
@@ -469,7 +451,7 @@ static int virtscsi_queuecommand(struct Scsi_Host *sh, struct scsi_cmnd *sc)
 	BUG_ON(sc->cmd_len > VIRTIO_SCSI_CDB_SIZE);
 	memcpy(cmd->req.cmd.cdb, sc->cmnd, sc->cmd_len);
 
-	if (virtscsi_kick_cmd(tgt, &vscsi->req_vq, cmd,
+	if (virtscsi_kick_cmd(&vscsi->req_vq, cmd,
 			      sizeof cmd->req.cmd, sizeof cmd->resp.cmd,
 			      GFP_ATOMIC) == 0)
 		ret = 0;
@@ -483,11 +465,10 @@ out:
 static int virtscsi_tmf(struct virtio_scsi *vscsi, struct virtio_scsi_cmd *cmd)
 {
 	DECLARE_COMPLETION_ONSTACK(comp);
-	struct virtio_scsi_target_state *tgt = vscsi->tgt[cmd->sc->device->id];
 	int ret = FAILED;
 
 	cmd->comp = ∁
-	if (virtscsi_kick_cmd(tgt, &vscsi->ctrl_vq, cmd,
+	if (virtscsi_kick_cmd(&vscsi->ctrl_vq, cmd,
 			      sizeof cmd->req.tmf, sizeof cmd->resp.tmf,
 			      GFP_NOIO) < 0)
 		goto out;
@@ -588,20 +569,16 @@ static void virtscsi_init_vq(struct virtio_scsi_vq *virtscsi_vq,
 }
 
 static struct virtio_scsi_target_state *virtscsi_alloc_tgt(
-	struct virtio_device *vdev, int sg_elems)
+	struct virtio_device *vdev)
 {
 	struct virtio_scsi_target_state *tgt;
 	gfp_t gfp_mask = GFP_KERNEL;
 
-	/* We need extra sg elements at head and tail.  */
-	tgt = kmalloc(sizeof(*tgt) + sizeof(tgt->sg[0]) * (sg_elems + 2),
-		      gfp_mask);
-
+	tgt = kmalloc(sizeof(*tgt), gfp_mask);
 	if (!tgt)
 		return NULL;
 
 	spin_lock_init(&tgt->tgt_lock);
-	sg_init_table(tgt->sg, sg_elems + 2);
 	return tgt;
 }
 
@@ -635,7 +612,7 @@ static int virtscsi_init(struct virtio_device *vdev,
 {
 	int err;
 	struct virtqueue *vqs[3];
-	u32 i, sg_elems;
+	u32 i;
 
 	vq_callback_t *callbacks[] = {
 		virtscsi_ctrl_done,
@@ -663,11 +640,8 @@ static int virtscsi_init(struct virtio_device *vdev,
 	if (virtio_has_feature(vdev, VIRTIO_SCSI_F_HOTPLUG))
 		virtscsi_kick_event_all(vscsi);
 
-	/* We need to know how many segments before we allocate.  */
-	sg_elems = virtscsi_config_get(vdev, seg_max) ?: 1;
-
 	for (i = 0; i < num_targets; i++) {
-		vscsi->tgt[i] = virtscsi_alloc_tgt(vdev, sg_elems);
+		vscsi->tgt[i] = virtscsi_alloc_tgt(vdev);
 		if (!vscsi->tgt[i]) {
 			err = -ENOMEM;
 			goto out;