Messages in this thread | | | Date | Tue, 4 Jul 2023 09:48:53 +0200 | From | Roger Pau Monné <> | Subject | Re: [PATCH 2/2] xen/virtio: Avoid use of the dom0 backend in dom0 |
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On Thu, Jun 29, 2023 at 03:44:04PM -0700, Stefano Stabellini wrote: > On Thu, 29 Jun 2023, Oleksandr Tyshchenko wrote: > > On 29.06.23 04:00, Stefano Stabellini wrote: > > > I think we need to add a second way? It could be anything that can help > > > us distinguish between a non-grants-capable virtio backend and a > > > grants-capable virtio backend, such as: > > > - a string on xenstore > > > - a xen param > > > - a special PCI configuration register value > > > - something in the ACPI tables > > > - the QEMU machine type > > > > > > Yes, I remember there was a discussion regarding that. The point is to > > choose a solution to be functional for both PV and HVM *and* to be able > > to support a hotplug. IIRC, the xenstore could be a possible candidate. > > xenstore would be among the easiest to make work. The only downside is > the dependency on xenstore which otherwise virtio+grants doesn't have.
I would avoid introducing a dependency on xenstore, if nothing else we know it's a performance bottleneck.
We would also need to map the virtio device topology into xenstore, so that we can pass different options for each device.
> Vikram is working on virtio with grants support in QEMU as we speak. > Maybe we could find a way to add a flag in QEMU so that we can detect at > runtime if a given virtio device support grants or not.
Isn't there a way for the device to expose capabilities already? For example how does a virtio-blk backend expose support for indirect descriptors?
Thanks, Roger.
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