linux-kernel - Re: [PATCH] hwrng: core - Allow for multiple simultaneous active hwrng devices

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Date:	Tue, 9 Aug 2016 16:57:10 +0000
From:	Jason Cooper <jason@...edaemon.net>
To:	Herbert Xu <herbert@...dor.apana.org.au>
Cc:	Keith Packard <keithp@...thp.com>, linux-crypto@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] hwrng: core - Allow for multiple simultaneous active
 hwrng devices

Hi Keith, Herbert,

On Tue, Aug 09, 2016 at 05:50:58PM +0800, Herbert Xu wrote:
> On Mon, Jul 25, 2016 at 01:07:35PM -0700, Keith Packard wrote:
> > Instead of having only one hwrng feeding /dev/random at a time, maintain
> > a list of devices and cycle between them when filling the entropy pool.
> > 
> > Signed-off-by: Keith Packard <keithp@...thp.com>
> 
> So you're cycling RNGs even for user-space reads? That could be
> problematic because not all hardware RNGs carry the maximum amount
> of entropy.  It would be rather annoying to be cycling between
> RNGs of different qualities.
> 
> Perhaps only cycle for the kernel hwrngd?

Perhaps a /dev/hwrng[0-9] per rng?  That would lend itself nicely to a
sysfs interface for per device quality, rate, and enabled attributes.
e.g. /sys/class/hw_random/hwrng0/{device/,quality,rate,enabled}

/dev/hwrng could pull from the one with the highest quality, or user
specified for backwards compatibility.

thx,

Jason.