RE: [PATCH v6 12/24] vfio/pci: Allow passing zero-length fd array in VFIO_DEVICE_PCI_HOT_RESET

Tian, Kevin
2023-03-24T09:10:05Z

> From: Alex Williamson <alex.williamson@redhat.com>
> Sent: Wednesday, March 22, 2023 5:01 AM
>
> On Tue, 21 Mar 2023 17:50:08 -0300
> Jason Gunthorpe <jgg@nvidia.com> wrote:
>
> >
> > Though it would be nice if qemu didn't need two implementations so Yi
> > I'd rather see a new info in this series as well and qemu can just
> > consistently use dev_id and never bdf in iommufd mode.
>
> We also need to consider how libvirt determines if QEMU has the kernel
> support it needs to pass file descriptors. It'd be a lot cleaner if
> this aligned with the introduction of vfio cdevs.
>

Libvirt can check whether the kernel creates cdev for a given device
via sysfs.

but I'm not sure how Libvirt determines whether QEMU supports a
feature that it wants to use. But sounds this is a general handshake
problem as Libvirt needs to support many versions of QEMU then
there must be a way for such negotiation?