linux-kernel - Re: [PATCH 1/2] rngd: add udev rule to source from hwrng if virtio-rng present

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Message-ID: <20140811133030.GA27247@lst.de>
Date:	Mon, 11 Aug 2014 15:30:30 +0200
From:	Torsten Duwe <duwe@....de>
To:	Amit Shah <amit.shah@...hat.com>
Cc:	"H. Peter Anvin" <hpa@...ux.intel.com>, jgarzik@...pay.com,
	Virtualization List <virtualization@...ts.linux-foundation.org>,
	Amos Kong <akong@...hat.com>,
	Rusty Russell <rusty@...tcorp.com.au>,
	linux-kernel@...r.kernel.org,
	Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>
Subject: Re: [PATCH 1/2] rngd: add udev rule to source from hwrng if
	virtio-rng present

On Mon, Aug 11, 2014 at 12:45:27PM +0530, Amit Shah wrote:
> 
> What's the suggested value for rng->quality, though, for virtio-rng
> that I can use to ensure the kthread starts?
> 
> Should I use the 700 (70%) as proposed in the original patchset?  I'm
> not exactly sure how that value will be used as well..

There is no such thing as a suggested value, every number is wrong
to some degree.  The quality is an estimation of how random your
source really is; it's a property of your hardware. If the device is
virtual you're in trouble ;-)

Either you have a way to query the underlying real hardware, or
you do your whitening and entropy estimation in the backend driver --
then you can claim 100%.

	Torsten

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