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Date: Wed, 20 Jun 2012 09:36:33 +0100
From: "Daniel P. Berrange" <berrange@redhat.com>
Message-ID: <20120620083633.GE20792@redhat.com>
References: <cover.1340175058.git.amit.shah@redhat.com>
	<c1837c529e302b013d3b513e254522725b457734.1340175058.git.amit.shah@redhat.com>
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In-Reply-To: <c1837c529e302b013d3b513e254522725b457734.1340175058.git.amit.shah@redhat.com>
Subject: Re: [Qemu-devel] [PATCH v3 1/1] virtio-rng: hardware random number
 generator device
Reply-To: "Daniel P. Berrange" <berrange@redhat.com>
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To: Amit Shah <amit.shah@redhat.com>
Cc: qemu list <qemu-devel@nongnu.org>, Anthony Liguori <anthony@codemonkey.ws>

On Wed, Jun 20, 2012 at 12:29:32PM +0530, Amit Shah wrote:
> The Linux kernel already has a virtio-rng driver, this is the device
> implementation.
> 
> When the guest asks for entropy from the virtio hwrng, it puts a buffer
> in the vq.  We then put entropy into that buffer, and push it back to
> the guest.
> 
> The chardev connected to this device is fed the data to be sent to the
> guest.
> 
> Invocation is simple:
> 
>   $ qemu ... -device virtio-rng-pci,chardev=foo
> 
> In the guest, we see
> 
>   $ cat /sys/devices/virtual/misc/hw_random/rng_available
>   virtio
> 
>   $ cat /sys/devices/virtual/misc/hw_random/rng_current
>   virtio
> 
>   # cat /dev/hwrng
> 
> Simply feeding /dev/urandom from the host to the chardev is sufficient:
> 
>   $ qemu ... -chardev socket,path=/tmp/foo,server,nowait,id=foo \
>              -device virtio-rng,chardev=foo
> 
>   $ nc -U /tmp/foo < /dev/urandom
> 
> A QMP event is sent for interested apps to monitor activity and send the
> appropriate number of bytes that get asked by the guest:
> 
>   {"timestamp": {"seconds": 1337966878, "microseconds": 517009}, \
>    "event": "ENTROPY_NEEDED", "data": {"bytes": 64}}
> 
> Signed-off-by: Amit Shah <amit.shah@redhat.com>

ACK to this from a libvirt design requirements POV.

Regards,
Daniel
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