Re: [Qemu-ppc] [PATCH v2 2/2] ppc/spapr_hcall: Implement H_RANDOM hypercall in QEMU

[Michael Ellerman]

On Wed, 2015-09-02 at 17:48 +1000, David Gibson wrote:
> On Wed, Sep 02, 2015 at 11:04:12AM +0530, Amit Shah wrote:
> > On (Mon) 31 Aug 2015 [20:46:02], Thomas Huth wrote:
> > > The PAPR interface provides a hypercall to pass high-quality
> > > hardware generated random numbers to guests. So let's provide
> > > this call in QEMU, too, so that guests that do not support
> > > virtio-rnd yet can get good random numbers, too.
> > 
> > virtio-rng, not rnd.
> > 
> > Can you elaborate what you mean by 'guests that do not support
> > virtio-rng yet'?  The Linux kernel has had the virtio-rng driver since
> > 2.6.26, so I'm assuming that's not the thing you're alluding to.
> > 
> > Not saying this hypercall isn't a good idea, just asking why.  I think
> > there's are valid reasons like the driver fails to load, or the driver
> > is compiled out, or simply is loaded too late in the boot cycle.
> 
> Yeah, I think we'd be talking about guests that just don't have it
> configured, although I suppose it's possible someone out there is
> using something earlier than 2.6.26 as well.  Note that H_RANDOM has
> been supported under PowerVM for a long time, and PowerVM doesn't have
> any virtio support.  So it is plausible that there are guests out
> there with with H_RANDOM support but no virtio-rng support, although I
> don't know of any examples specifically.  RHEL6 had virtio support,
> including virtio-rng more or less by accident (since it was only
> supported under PowerVM).  SLES may not have made the same fortunate
> error - I don't have a system handy to check.

There also could be folks who want to run non-Linux operating systems, which
don't have a virtio-rng driver, crazy I know :)

cheers