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

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Message-Id: <20190809064847.28918-3-pagupta@redhat.com>
Date:   Fri,  9 Aug 2019 12:18:47 +0530
From:   Pankaj Gupta <pagupta@...hat.com>
To:     amit@...nel.org, mst@...hat.com
Cc:     arnd@...db.de, gregkh@...uxfoundation.org,
        virtualization@...ts.linux-foundation.org, jasowang@...hat.com,
        linux-kernel@...r.kernel.org, pagupta@...hat.com,
        xiaohli@...hat.com
Subject: [PATCH v3 2/2] virtio: decrement avail idx with buffer detach for packed ring

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 <pagupta@...hat.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