From mboxrd@z Thu Jan  1 00:00:00 1970
Received: from eggs.gnu.org ([2001:4830:134:3::10]:54220)
	by lists.gnu.org with esmtp (Exim 4.71)
	(envelope-from <rusty@ozlabs.org>) id 1YVriq-0003ni-PM
	for qemu-devel@nongnu.org; Wed, 11 Mar 2015 21:15:37 -0400
Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71)
	(envelope-from <rusty@ozlabs.org>) id 1YVrij-0003mG-53
	for qemu-devel@nongnu.org; Wed, 11 Mar 2015 21:15:36 -0400
Received: from ozlabs.org ([103.22.144.67]:47091)
	by eggs.gnu.org with esmtp (Exim 4.71)
	(envelope-from <rusty@ozlabs.org>) id 1YVrii-0003jJ-P5
	for qemu-devel@nongnu.org; Wed, 11 Mar 2015 21:15:29 -0400
From: Rusty Russell <rusty@rustcorp.com.au>
In-Reply-To: <20150311133242-mutt-send-email-mst@redhat.com>
References: <1426053572-21326-1-git-send-email-rusty@rustcorp.com.au>
	<20150311061935.GA13037@redhat.com>
	<20150311064747.GF1437@ad.nay.redhat.com>
	<20150311074938-mutt-send-email-mst@redhat.com>
	<87pp8fyddj.fsf@rustcorp.com.au>
	<20150311133242-mutt-send-email-mst@redhat.com>
Date: Thu, 12 Mar 2015 11:34:35 +1030
Message-ID: <87bnjzxbz0.fsf@rustcorp.com.au>
MIME-Version: 1.0
Content-Type: text/plain
Subject: Re: [Qemu-devel] [PATCH 0/2] virtio len fixes for qemu.
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: "Michael S. Tsirkin" <mst@redhat.com>
Cc: Fam Zheng <famz@redhat.com>, QEMU Developers <qemu-devel@nongnu.org>, stefanha@redhat.com

"Michael S. Tsirkin" <mst@redhat.com> writes:
> On Wed, Mar 11, 2015 at 10:06:40PM +1030, Rusty Russell wrote:
>>         Each entry in the ring is a pair: \field{id} indicates the head
>>         entry of the descriptor chain describing the buffer (this
>>         matches an entry placed in the available ring by the guest
>>         earlier), and \field{len} the total of bytes written into the
>>         buffer. The latter is extremely useful for drivers using
>>         untrusted buffers: if you do not know exactly how much has been
>>         written by the device, you usually have to zero the buffer to
>>         ensure no data leakage occurs.
>
> Right so what does this "if you do not know exactly how much has been
> written by the device" mean?

It means "without this feature, you would not know how much has been
written by the device"...

Should probably become a Note:

Cheers,
Rusty.