Re: [Qemu-devel] [PATCH 4/5] virtio-scsi: Add start/stop functionality for vhost-scsi

[Paolo Bonzini]

Il 10/09/2012 08:24, Michael S. Tsirkin ha scritto:
>> > I chose the backend name because, ideally, there would be no other
>> > difference.  QEMU _could_ implement all the goodies in vhost-scsi (such
>> > as reservations or ALUA), it just doesn't do that yet.
>> > 
>> > Paolo
> Then why do you say "It is used completely differently from
> virtio-scsi-pci"?

It is configured differently (and I haven't seen a proposal yet for how
to bridge the two), it does not interoperate, it has right now a
different set of features.

The "does not interoperate" bit is particularly important.  Say QEMU
were to implement persistent reservations (right now only a vhost-scsi
feature).  Then QEMU and vhost-scsi PR would not be interchangeable, a
reservation made by QEMU would not be visible in vhost and vice versa.

> Isn't it just a different backend?
> 
> If yes then it should be a backend option, like it is
> for virtio-net.

You mean a -drive option?  That would mean adding the logic to configure
vhost-scsi to the QEMU block layer, that's a completely different project...

Paolo