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

[David Gibson]

On Thu, Sep 03, 2015 at 11:21:24AM +1000, Michael Ellerman wrote:
> 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 :)

Well, yes.  Although I don't have any concrete examples of those, either..

-- 
David Gibson                    | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au  | minimalist, thank you.  NOT _the_ _other_
                                | _way_ _around_!
http://www.ozlabs.org/~dgibson

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