On Tue, May 28, 2013 at 01:53:35PM -0500, Anthony Liguori wrote:
> "Michael S. Tsirkin" <mst@xxxxxxxxxx> writes:
>
> > On Tue, May 28, 2013 at 12:15:16PM -0500, Anthony Liguori wrote:
> >> > @@ -455,6 +462,226 @@ static void virtio_pci_config_write(void *opaque, hwaddr addr,
> >> > }
> >> > }
> >> >
> >> > +static uint64_t virtio_pci_config_common_read(void *opaque, hwaddr addr,
> >> > + unsigned size)
> >> > +{
> >> > + VirtIOPCIProxy *proxy = opaque;
> >> > + VirtIODevice *vdev = proxy->vdev;
> >> > +
> >> > + uint64_t low = 0xffffffffull;
> >> > +
> >> > + switch (addr) {
> >> > + case offsetof(struct virtio_pci_common_cfg, device_feature_select):
> >> > + return proxy->device_feature_select;
> >>
> >> Oh dear no... Please use defines like the rest of QEMU.
> >
> > Any good reason not to use offsetof?
> > I see about 138 examples in qemu.
>
> There are exactly zero:
>
> $ find . -name "*.c" -exec grep -l "case offset" {} \;
> $
>
> > Anyway, that's the way Rusty wrote it in the kernel header -
> > I started with defines.
> > If you convince Rusty to switch I can switch too,
>
> We have 300+ devices in QEMU that use #defines. We're not using this
> kind of thing just because you want to copy code from the kernel.
Rusty, let's switch to defines?
> >> https://github.com/aliguori/qemu/commit/587c35c1a3fe90f6af0f97927047ef4d3182a659
> >>
> >> And:
> >>
> >> https://github.com/aliguori/qemu/commit/01ba80a23cf2eb1e15056f82b44b94ec381565cb
> >>
> >> Which lets virtio-pci be subclassable and then remaps the config space to
> >> BAR2.
> >
> >
> > Interesting. Have the spec anywhere?
>
> Not yet, but working on that.
>
> > You are saying this is going to conflict because
> > of BAR2 usage, yes?
>
> No, this whole thing is flexible. I had to use BAR2 because BAR0 has to
> be the vram mapping. It also had to be an MMIO bar.
>
> The new layout might make it easier to implement a device like this.
Absolutely, you can put thing anywhere you like.
> I
> shared it mainly because I wanted to show the subclassing idea vs. just
> tacking an option onto the existing virtio-pci code in QEMU.
>
> Regards,
>
> Anthony Liguori
I don't think a subclass will work for the new layout. This should be
completely transparent to users, just have more devices
work with more flexibility.
> > So let's only do this virtio-fb only for new layout, so we don't need
> > to maintain compatibility. In particular, we are working
> > on making memory BAR access fast for virtio devices
> > in a generic way. At the moment they are measureably slower
> > than PIO on x86.
> >
> >
> >> Haven't looked at the proposed new ring layout yet.
> >>
> >> Regards,
> >
> > No new ring layout. It's new config layout.
> >
> >
> > --
> > MST
> > --
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