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Date: Thu, 30 Jan 2014 13:56:52 +0100
From: Andrew Jones <drjones@redhat.com>
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Subject: Re: [Qemu-devel] [PATCH v3] virtio: Introduce virtio-testdev
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To: Mike Day <ncmike@ncultra.org>
Cc: peter.maydell@linaro.org, qemu-devel@nongnu.org, christoffer.dall@linaro.org, kvmarm@lists.cs.columbia.edu

On Thu, Jan 30, 2014 at 07:44:59AM -0500, Mike Day wrote:
> 
> Andrew Jones <drjones@redhat.com> writes:
> 
> > This is a virtio version of hw/misc/debugexit and should evolve into a
> > virtio version of pc-testdev. pc-testdev uses the PC's ISA bus, whereas
> > this testdev can be plugged into a virtio-mmio transport, which is
> > needed for kvm-unit-tests/arm. virtio-testdev uses the virtio device
> > config space as a communication channel, and implements an RTAS-like
> > protocol through it allowing guests to execute commands. Only three
> > commands are currently implemented;
> > 1) VERSION: for version compatibility checks
> > 2) CLEAR:   set all the config space back to zero
> > 3) EXIT:    exit() from qemu with a status code
> 
> > +static uint32_t virtio_testdev_get_features(VirtIODevice *vdev, uint32_t f)
> > +{
> > +    return f;
> > +}
> > +
> 
> Is this meant to be a stub currently? 
> 

Something like that. *_get_features() must be supplied by all virtio
devices. Just returning the requested features, f, rather than zero,
is how virtio-rng does it. So I went that way too.

drew