Re: VFIO Migration

[Stefan Hajnoczi]

On Wed, Nov 04, 2020 at 05:32:02PM +0000, Dr. David Alan Gilbert wrote:
> * Stefan Hajnoczi (stefanha@redhat.com) wrote:
> > Michael replied in another sub-thread wondering if versions are really
> > necessary since tools do the migration checks. Let's try dropping
> > versions to simplify things. We can bring them back if needed later.
> 
> What does a user facing tool do?  If I say I want one of these NICs
> and I'm on the latest QEMU machine type, who sets all these parameters?

The machine type is orthogonal since QEMU doesn't know about every
possible VFIO device. The device is like a PCI adapter that is added to
a physical machine aftermarket, it's not part of the base machine's
specs.

The migration tool queries the parameters from the source device.
VFIO/mdev will provide sysfs attrs. For vfio-user I'm not sure whether
to print the parameters during device instantiation, require a
VFIO-compatible FUSE directory, or to use a query-migration-params RPC
command.

Let's discuss this more when the next revision of the document is sent
out, because it modifies the approach so that migration parameters are
logically separate from device configuration parameters. That changes
things a bit.

Stefan

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