From mboxrd@z Thu Jan  1 00:00:00 1970
Received: from eggs.gnu.org ([208.118.235.92]:35332)
	by lists.gnu.org with esmtp (Exim 4.71)
	(envelope-from <anthony@codemonkey.ws>) id 1UBXBr-0002e1-8s
	for qemu-devel@nongnu.org; Fri, 01 Mar 2013 16:08:29 -0500
Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71)
	(envelope-from <anthony@codemonkey.ws>) id 1UBXBq-00019i-Ar
	for qemu-devel@nongnu.org; Fri, 01 Mar 2013 16:08:27 -0500
Received: from mail-oa0-f53.google.com ([209.85.219.53]:49125)
	by eggs.gnu.org with esmtp (Exim 4.71)
	(envelope-from <anthony@codemonkey.ws>) id 1UBXBq-00019Z-5n
	for qemu-devel@nongnu.org; Fri, 01 Mar 2013 16:08:26 -0500
Received: by mail-oa0-f53.google.com with SMTP id m1so6427137oag.26
	for <qemu-devel@nongnu.org>; Fri, 01 Mar 2013 13:08:25 -0800 (PST)
From: Anthony Liguori <anthony@codemonkey.ws>
In-Reply-To: <513110D3.5030503@linux.vnet.ibm.com>
References: <512FF819.7050505@redhat.com> <87k3pqzy2y.fsf@codemonkey.ws>
	<513110D3.5030503@linux.vnet.ibm.com>
Date: Fri, 01 Mar 2013 15:08:21 -0600
Message-ID: <87d2vig75m.fsf@codemonkey.ws>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Subject: Re: [Qemu-devel] virtio-rng and fd passing
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: Stefan Berger <stefanb@linux.vnet.ibm.com>
Cc: "qemu-devel@nongnu.org" <qemu-devel@nongnu.org>

Stefan Berger <stefanb@linux.vnet.ibm.com> writes:

> On 03/01/2013 03:04 PM, Anthony Liguori wrote:
>> Eric Blake <eblake@redhat.com> writes:
>>
>>> Stefan Berger and I discovered on IRC that virtio-rng is unable to
>>> support fd passing.  We attempted:
>>>
>>> qemu-system-x86_64 ... -add-fd set=4,fd=34,opaque=RDONLY:/dev/urandom
>>> -object rng-random,id=rng0,filename=/dev/fdset/4 -device
>>> virtio-rng-pci,rng=rng0,bus=pci.0,addr=0x6
>> Why are you using th rng-random backend instead of the rng-egd backend?
>
> I followed the example on the libvirt website trying out the XML for the 
> rng device while adpating the libvirt code to use fd passing and 
> generating the -add-fd command line parameters.
>
>>
>> You can pass chardevs to the egd backend.  It's really not a good idea
>> to pass a fd via rng-rangom.
>
> Fine, then we won't use fd passing for this device, whatever the reason 
> may be.

So let's step back.  There are two backends currently supported:
rng-random and rng-egd.  I don't see any point in taking an fd for
rng-random.  I don't think labeling comes into play here.

But if libvirt wants to interact with virtio-rng in a more intelligent
way (implementing a policy to distribute entropy), then rng-egd is the
right way to do that.

Regards,

Anthony Liguori

>
>     Stefan