On Thu, Nov 05, 2020 at 12:13:24PM +0000, Dr. David Alan Gilbert wrote: > * Stefan Hajnoczi (stefa...@redhat.com) wrote: > > On Wed, Nov 04, 2020 at 05:32:02PM +0000, Dr. David Alan Gilbert wrote: > > > * Stefan Hajnoczi (stefa...@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. > > OK, but ignoring migration, I think the same problem holds; if I'm a > tool creating one of these VMs, and I plug this device in, what do I do > with all it's configuration parameters? I'd assume most of the time > that they don't know about or dont care about most of the parameters, > they just want the sane defaults unless told otherwise.
I think that if you ignore migration then you can ignore parameters. > > 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. > > But on VM creation we have to answer the question of what config do we > want; so for example lets say I'm creating a new VM in my cluster, > but I want to be sure that later I can migrate it. I can read the > config off one of the other machines; can I just use that even if my > new machine has a later device implementation? > > Dave I don't think so - we need a tool that can query a set of machines and then produce a safe configuration. The same problem exists with vhost as well it will just explode exponentially with lots more devices and backends ... Talked about it a bit in my kvm forum preso ... > > 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 > > > -- > Dr. David Alan Gilbert / dgilb...@redhat.com / Manchester, UK
