virtio-ring: maintain next in extra state for packed virtqueue

This patch moves next from vring_desc_state_packed to
vring_desc_desc_extra_packed. This makes it simpler to let extra state
to be reused by split virtqueue.
Signed-off-by: Jason Wang <jasowang@redhat.com>
Link: https://lore.kernel.org/r/20210604055350.58753-2-jasowang@redhat.comSigned-off-by: Michael S. Tsirkin <mst@redhat.com>

drivers/virtio/virtio_ring.c

@@ -74,7 +74,6 @@ struct vring_desc_state_packed {
 	void *data;			/* Data for callback. */
 	struct vring_packed_desc *indir_desc; /* Indirect descriptor, if any. */
 	u16 num;			/* Descriptor list length. */
-	u16 next;			/* The next desc state in a list. */
 	u16 last;			/* The last desc state in a list. */
 };
 
@@ -82,6 +81,7 @@ struct vring_desc_extra_packed {
 	dma_addr_t addr;		/* Buffer DMA addr. */
 	u32 len;			/* Buffer length. */
 	u16 flags;			/* Descriptor flags. */
+	u16 next;			/* The next desc state in a list. */
 };
 
 struct vring_virtqueue {
@@ -1067,7 +1067,7 @@ static int virtqueue_add_indirect_packed(struct vring_virtqueue *vq,
 				1 << VRING_PACKED_DESC_F_USED;
 	}
 	vq->packed.next_avail_idx = n;
-	vq->free_head = vq->packed.desc_state[id].next;
+	vq->free_head = vq->packed.desc_extra[id].next;
 
 	/* Store token and indirect buffer state. */
 	vq->packed.desc_state[id].num = 1;
@@ -1175,7 +1175,7 @@ static inline int virtqueue_add_packed(struct virtqueue *_vq,
 					le16_to_cpu(flags);
 			}
 			prev = curr;
-			curr = vq->packed.desc_state[curr].next;
+			curr = vq->packed.desc_extra[curr].next;
 
 			if ((unlikely(++i >= vq->packed.vring.num))) {
 				i = 0;
@@ -1296,7 +1296,7 @@ static void detach_buf_packed(struct vring_virtqueue *vq,
 	/* Clear data ptr. */
 	state->data = NULL;
 
-	vq->packed.desc_state[state->last].next = vq->free_head;
+	vq->packed.desc_extra[state->last].next = vq->free_head;
 	vq->free_head = id;
 	vq->vq.num_free += state->num;
 
@@ -1305,7 +1305,7 @@ static void detach_buf_packed(struct vring_virtqueue *vq,
 		for (i = 0; i < state->num; i++) {
 			vring_unmap_state_packed(vq,
 				&vq->packed.desc_extra[curr]);
-			curr = vq->packed.desc_state[curr].next;
+			curr = vq->packed.desc_extra[curr].next;
 		}
 	}
 
@@ -1656,8 +1656,6 @@ static struct virtqueue *vring_create_virtqueue_packed(
 
 	/* Put everything in free lists. */
 	vq->free_head = 0;
-	for (i = 0; i < num-1; i++)
-		vq->packed.desc_state[i].next = i + 1;
 
 	vq->packed.desc_extra = kmalloc_array(num,
 			sizeof(struct vring_desc_extra_packed),
@@ -1668,6 +1666,9 @@ static struct virtqueue *vring_create_virtqueue_packed(
 	memset(vq->packed.desc_extra, 0,
 		num * sizeof(struct vring_desc_extra_packed));
 
+	for (i = 0; i < num - 1; i++)
+		vq->packed.desc_extra[i].next = i + 1;
+
 	/* No callback?  Tell other side not to bother us. */
 	if (!callback) {
 		vq->packed.event_flags_shadow = VRING_PACKED_EVENT_FLAG_DISABLE;