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Subject: Re: [PATCH v3 2/2] virtio: decrement avail idx with buffer detach for
 packed ring
To:     Pankaj Gupta <pagupta@redhat.com>, amit@kernel.org, mst@redhat.com
Cc:     arnd@arndb.de, gregkh@linuxfoundation.org,
        virtualization@lists.linux-foundation.org,
        linux-kernel@vger.kernel.org, xiaohli@redhat.com
References: <20190809064847.28918-1-pagupta@redhat.com>
 <20190809064847.28918-3-pagupta@redhat.com>
From:   Jason Wang <jasowang@redhat.com>
Message-ID: <b1ab613d-55a4-fdb4-96b1-03bedbcc740b@redhat.com>
Date:   Mon, 12 Aug 2019 12:46:54 +0800
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On 2019/8/9 下午2:48, Pankaj Gupta wrote:
> 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@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;
>   	}


Acked-by: Jason Wang <jasowang@redhat.com>