Re: [Qemu-devel] [PATCH v3] ppc/spapr: Implement H_RANDOM hypercall in QEMU

[Amit Shah <amit.shah@redhat.com>]

On (Tue) 15 Sep 2015 [14:26:06], David Gibson wrote:
> On Mon, Sep 14, 2015 at 08:32:36AM +0200, Thomas Huth wrote:
> > On 14/09/15 04:15, David Gibson wrote:
> > > On Fri, Sep 11, 2015 at 11:17:01AM +0200, Thomas Huth wrote:
> > >> The PAPR interface defines a hypercall to pass high-quality
> > >> hardware generated random numbers to guests. Recent kernels can
> > >> already provide this hypercall to the guest if the right hardware
> > >> random number generator is available. But in case the user wants
> > >> to use another source like EGD, or QEMU is running with an older
> > >> kernel, we should also have this call in QEMU, so that guests that
> > >> do not support virtio-rng yet can get good random numbers, too.
> > >>
> > >> This patch now adds a new pseude-device to QEMU that either
> > >> directly provides this hypercall to the guest or is able to
> > >> enable the in-kernel hypercall if available. The in-kernel
> > >> hypercall can be enabled with the use-kvm property, e.g.:
> > >>
> > >>  qemu-system-ppc64 -device spapr-rng,use-kvm=true
> > >>
> > >> For handling the hypercall in QEMU instead, a RngBackend is required
> > >> since the hypercall should provide "good" random data instead of
> > >> pseudo-random (like from a "simple" library function like rand()
> > >> or g_random_int()). Since there are multiple RngBackends available,
> > >> the user must select an appropriate backend via the "backend"
> > >> property of the device, e.g.:
> > >>
> > >>  qemu-system-ppc64 -object rng-random,filename=/dev/hwrng,id=rng0 \
> > >>                    -device spapr-rng,backend=rng0 ...

(snip)

> > > More importantly, this should probably be called "rng" not "backend"
> > > to match virtio-rng.
> > 
> > Since the device is already called "spapr-rng", i.e. has "rng" in its
> > name, I'd rather like to keep this as "backend" to make it clear that
> > you specify the backend this way.
> 
> Hm, personally I'd weigh consistency with virtio-rng higher than the
> slightly confusing name.

Agreed.

		Amit