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

[Felipe Franciosi]

> On 7 Jun 2017, at 17:21, Paolo Bonzini <address@hidden> wrote:
> 
> 
> 
> On 07/06/2017 17:39, Felipe Franciosi wrote:
>> 
>>> On 7 Jun 2017, at 16:37, Peter Maydell <address@hidden> wrote:
>>> 
>>> On 7 June 2017 at 16:28, Paolo Bonzini <address@hidden> wrote:
>>>> From: Felipe Franciosi <address@hidden>
>>>> 
>>>> This commit introduces a vhost-user device for SCSI. This is based
>>>> on the existing vhost-scsi implementation, but done over vhost-user
>>>> instead. It also uses a chardev to connect to the backend. Unlike
>>>> vhost-scsi (today), VMs using vhost-user-scsi can be live migrated.
>>>> 
>>>> To use it, start Qemu with a command line equivalent to:
>>>> 
>>>> qemu-system-x86_64 \
>>>>      -chardev socket,id=vus0,path=/tmp/vus.sock \
>>>>      -device vhost-user-scsi-pci,chardev=vus0,bus=pci.0,addr=...
>>>> 
>>>> A separate commit presents a sample application linked with libiscsi to
>>>> provide a backend for vhost-user-scsi.
>>>> 
>>>> Signed-off-by: Felipe Franciosi <address@hidden>
>>>> Message-Id: <address@hidden>
>>>> [Disable migration for now, since it does not support bdrv_drain. - Paolo]
>>> 
>>> I was expecting this to mean a VMStateDescription with a
>>> ".unmigratable = 1" field, but it doesn't seem to have one.
>>> Does it disable migration some other way?
>> 
>> Hi Peter,
>> 
>> vhost-user-scsi supports migration.
> 
> How, since there is no synchronization point between the vhost-user
> server on the source and the destination?

The idea is that the backend should both stop picking up new requests and also 
quiesce outstanding requests upon a GET_VRING_BASE vhost message.

> 
> 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