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

[Jason Cooper]

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@xxxxxxxxxx>
> 
> 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.