[PATCH v3 2/2] virtio: decrement avail idx with buffer detach for packed ring

[Pankaj Gupta]

This patch decrements 'next_avail_idx' count when detaching a buffer
from vq for packed ring code. Split ring code already does this in
virtqueue_detach_unused_buf_split function. This updates the
'next_avail_idx' to the previous correct index after an unused buffer
is detatched from the vq.

Signed-off-by: Pankaj Gupta <pagu...@redhat.com>
---
 drivers/virtio/virtio_ring.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
index c8be1c4f5b55..7c69181113e2 100644
--- a/drivers/virtio/virtio_ring.c
+++ b/drivers/virtio/virtio_ring.c
@@ -1537,6 +1537,12 @@ static void *virtqueue_detach_unused_buf_packed(struct 
virtqueue *_vq)
                /* detach_buf clears data, so grab it now. */
                buf = vq->packed.desc_state[i].data;
                detach_buf_packed(vq, i, NULL);
+               vq->packed.next_avail_idx--;
+               if (vq->packed.next_avail_idx < 0) {
+                       vq->packed.next_avail_idx = vq->packed.vring.num - 1;
+                       vq->packed.avail_wrap_counter ^= 1;
+               }
+
                END_USE(vq);
                return buf;
        }
-- 
2.20.1