Re: [Qemu-devel] [PULL 18/33] vhost-user-scsi: Introduce vhost-user-scsi host device

[Paolo Bonzini <pbonzini@redhat.com>]

> > This could be documented,
> 
> It is documented AFAIK. Pls take a look at the spec documentation.

Found it now.  It's not under GET_VRING_BASE, it's under "starting
and stopping rings"---fair enough.

In the case of vhost-user-scsi, however, QEMU also must not proceed
until vhost-user-scsi has drained the pending I/O---and this pending
I/O would be completed _after_ QEMU has sent GET_VRING_BASE.

Is this handled by VHOST_USER_PROTOCOL_F_REPLY_ACK already?  If so,
migration would be denied if the server lacks that protocol feature.

Paolo

> > but perhaps it's best to add a START_STOP
> > feature and message to the vhost-user protocol?
> 
> We just never need to GET_VRING_BASE if ring keeps going -
> makes no sense since base gets invalidated immediately.
> 
> 
> 
> > The feature then can be optional for vhost-user-net and mandatory for
> > vhost-user-scsi.  When this is done we can remove .unmigratable.
> > 
> > Thanks,
> > 
> > Paolo
> 
> If vhost-user-scsi does not stop the ring after responding to
> GET_VRING_BASE, it's just a bug that needs to be fixed.
> 
> > > > 
> > > > Can you please send a version of your patch that uses .unmigratable?
> > > 
> > > Sure I can do that. We can work on the migration later on.
> > > 
> > > > 
> > > > I'll send a v6 that momentarily drops vhost-scsi, but I intend to
> > > > include it again in the next pull request.
> > > 
> > > Sounds good to me.
> > > 
> > > Felipe
> > > 
> > > > 
> > > > Thanks,
> > > > 
> > > > Paolo
> > > 
> > > 
>