[RFC PATCH 08/16] virtio_ring: packed: extract next_idx()

[Xuan Zhuo <xuanzhuo@xxxxxxxxxxxxxxxxx>]

Separate the logic of idx growth of packed into a function. It is
convenient to share in multiple locations. Subsequent patches will also
use this logic.

Signed-off-by: Xuan Zhuo <xuanzhuo@xxxxxxxxxxxxxxxxx>
---
 drivers/virtio/virtio_ring.c | 30 +++++++++++++++++-------------
 1 file changed, 17 insertions(+), 13 deletions(-)

diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
index fa4270e8c009..e3525d92f646 100644
--- a/drivers/virtio/virtio_ring.c
+++ b/drivers/virtio/virtio_ring.c
@@ -1330,6 +1330,18 @@ static int virtqueue_resize_split(struct virtqueue *_vq, u32 num,
  * Packed ring specific functions - *_packed().
  */
 
+static u32 next_idx(struct vring_virtqueue *vq, u32 idx)
+{
+	if ((unlikely(++idx >= vq->packed.vring.num))) {
+		idx = 0;
+		vq->packed.avail_used_flags ^=
+			1 << VRING_PACKED_DESC_F_AVAIL |
+			1 << VRING_PACKED_DESC_F_USED;
+	}
+
+	return idx;
+}
+
 static void vring_unmap_extra_packed(const struct vring_virtqueue *vq,
 				     struct vring_desc_extra *extra)
 {
@@ -1465,14 +1477,11 @@ static int virtqueue_add_indirect_packed(struct vring_virtqueue *vq,
 	vq->vq.num_free -= 1;
 
 	/* Update free pointer */
-	n = head + 1;
-	if (n >= vq->packed.vring.num) {
-		n = 0;
+	n = next_idx(vq, head);
+
+	if (n < head)
 		vq->packed.avail_wrap_counter ^= 1;
-		vq->packed.avail_used_flags ^=
-				1 << VRING_PACKED_DESC_F_AVAIL |
-				1 << VRING_PACKED_DESC_F_USED;
-	}
+
 	vq->packed.next_avail_idx = n;
 	vq->free_head = vq->packed.desc_extra[id].next;
 
@@ -1592,12 +1601,7 @@ static inline int virtqueue_add_packed(struct virtqueue *_vq,
 			prev = curr;
 			curr = vq->packed.desc_extra[curr].next;
 
-			if ((unlikely(++i >= vq->packed.vring.num))) {
-				i = 0;
-				vq->packed.avail_used_flags ^=
-					1 << VRING_PACKED_DESC_F_AVAIL |
-					1 << VRING_PACKED_DESC_F_USED;
-			}
+			i = next_idx(vq, i);
 		}
 	}
 
-- 
2.31.0

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