Re: [Qemu-devel] [PATCH 2/2] virtio-scsi: Implement hotplug support for virtio-scsi

[mc@linux.vnet.ibm.com]

Quoting Stefan Hajnoczi <stefanha@gmail.com>:

> On Wed, Jun 20, 2012 at 7:47 AM, Cong Meng <mc@linux.vnet.ibm.com> wrote:
>> Implement the hotplug() and hot_unplug() interfaces in virtio-scsi,  
>> by signal
>> the virtio_scsi.ko in guest kernel via event virtual queue.
>>
>> The counterpart patch of virtio_scsi.ko will be sent soon in another thread.
>
>> Signed-off-by: Cong Meng <mc@linux.vnet.ibm.com>
>> Signed-off-by: Sen Wang <senwang@linux.vnet.ibm.com>
>> ---
>>  hw/virtio-scsi.c |   72  
>> +++++++++++++++++++++++++++++++++++++++++++++++++++--
>>  1 files changed, 69 insertions(+), 3 deletions(-)
>
> I compared against the virtio-scsi specification and this looks good:
> http://ozlabs.org/~rusty/virtio-spec/virtio-0.9.5.pdf
>
> Dropped events and event throttling are not implemented by this patch.
>  This means that the guest can miss events if it runs out of event
> queue elements.  A scenario that might be able to trigger this is if
> multiple LUNs are hotplugged in a single QEMU monitor callback.
>
> Implementing dropped events is easy in hw/virtio-scsi.c.  Keep a bool
> or counter of dropped events and report them when the guest kicks us
> with a free event element (virtio_scsi_handle_event).

Yes. It's easy to do this in qemu. But I'm not sure what should be done
in virtio-scsi.ko to respond the "VIRTIO_SCSI_T_EVENTS_MISSED" event.
The spec says "poll the logical units for unit attention conditions", or
just a whole bus rescan?

>
> Stefan