From mboxrd@z Thu Jan  1 00:00:00 1970
Received: from eggs.gnu.org ([2001:4830:134:3::10]:36817)
	by lists.gnu.org with esmtp (Exim 4.71)
	(envelope-from <catalin.vasile@freescale.com>) id 1YMDmX-0007PX-Jb
	for qemu-devel@nongnu.org; Fri, 13 Feb 2015 05:47:34 -0500
Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71)
	(envelope-from <catalin.vasile@freescale.com>) id 1YMDmU-0005pT-E4
	for qemu-devel@nongnu.org; Fri, 13 Feb 2015 05:47:33 -0500
Received: from mail-bl2on0111.outbound.protection.outlook.com
	([65.55.169.111]:14253
	helo=na01-bl2-obe.outbound.protection.outlook.com)
	by eggs.gnu.org with esmtp (Exim 4.71)
	(envelope-from <catalin.vasile@freescale.com>) id 1YMDmU-0005pN-8v
	for qemu-devel@nongnu.org; Fri, 13 Feb 2015 05:47:30 -0500
Message-ID: <54DDD637.808@freescale.com>
Date: Fri, 13 Feb 2015 12:47:19 +0200
From: Vasile Catalin-B50542 <catalin.vasile@freescale.com>
MIME-Version: 1.0
References: <54DCB016.8030509@freescale.com>
In-Reply-To: <54DCB016.8030509@freescale.com>
Content-Type: text/plain; charset="utf-8"; format=flowed
Content-Transfer-Encoding: 7bit
Subject: Re: [Qemu-devel] [virtio] virtqueue request size
List-Id: <qemu-devel.nongnu.org>
List-Unsubscribe: <https://lists.nongnu.org/mailman/options/qemu-devel>,
	<mailto:qemu-devel-request@nongnu.org?subject=unsubscribe>
List-Archive: <http://lists.nongnu.org/archive/html/qemu-devel>
List-Post: <mailto:qemu-devel@nongnu.org>
List-Help: <mailto:qemu-devel-request@nongnu.org?subject=help>
List-Subscribe: <https://lists.nongnu.org/mailman/listinfo/qemu-devel>,
	<mailto:qemu-devel-request@nongnu.org?subject=subscribe>
To: qemu-devel@nongnu.org

I found out what was the problem.
I was calling virtqueue_get_avail_bytes() after virtqueue_pop().

On 12.02.2015 15:52, Vasile Catalin-B50542 wrote:
> I'm trying to work out virtqueue from the virtio API.
> I've been able to send a message from guest to qemu, but there is 
> something
> strange that I don't understand.
> virtqueue_get_avail_bytes() returns 0 number of "in" bytes, but if I 
> hard code
> iov_to_buf() to get 5 bytes, it actually gets my message.
> What am I missing out?
>
> Here is the essential code so far:
> Guest:
>     probe function:
>         vq = virtio_find_single_vq(vdev, recv_done, "input");
>     triggered send function:
>         sg_init_one(&sg, buf, size);
>         if (virtqueue_add_inbuf(vq, &sg, 1, buf, GFP_KERNEL) < 0)
>             BUG();
>         virtqueue_kick(vq);
>
> Qemu:
>     realize function:
>         vcrypto->vq = virtio_add_queue(vdev, 8, handle_input);
>     handle_input:
>         virtqueue_pop(vcrypto->vq, &elem);
>         eprintf("request size is %u", get_request_size(vcrypto->vq, 
> 100)); // prints size 0
>         iov_to_buf(elem.in_sg, elem.in_num, 0, buffer, 5); // 
> hardcoded to 5 bytes for now
>     get_request_size:
>         virtqueue_get_avail_bytes(vq, &in, &out, quota, quota); // 
> quota = 100
>         return in;