Re: [PATCH] Rescan the entire target on transport reset when LUN is 0

[Felipe Franciosi <felipe@nutanix.com>]

> On Sep 8, 2020, at 3:22 PM, Paolo Bonzini <pbonzini@redhat.com> wrote:
> 
> On 28/08/20 14:21, Matej Genci wrote:
>> VirtIO 1.0 spec says
>>    The removed and rescan events ... when sent for LUN 0, they MAY
>>    apply to the entire target so the driver can ask the initiator
>>    to rescan the target to detect this.
>> 
>> This change introduces the behaviour described above by scanning the
>> entire scsi target when LUN is set to 0. This is both a functional and a
>> performance fix. It aligns the driver with the spec and allows control
>> planes to hotplug targets with large numbers of LUNs without having to
>> request a RESCAN for each one of them.
>> 
>> Signed-off-by: Matej Genci <matej@nutanix.com>
>> Suggested-by: Felipe Franciosi <felipe@nutanix.com>
>> ---
>> drivers/scsi/virtio_scsi.c | 7 ++++++-
>> 1 file changed, 6 insertions(+), 1 deletion(-)
>> 
>> diff --git a/drivers/scsi/virtio_scsi.c b/drivers/scsi/virtio_scsi.c
>> index bfec84aacd90..a4b9bc7b4b4a 100644
>> --- a/drivers/scsi/virtio_scsi.c
>> +++ b/drivers/scsi/virtio_scsi.c
>> @@ -284,7 +284,12 @@ static void virtscsi_handle_transport_reset(struct virtio_scsi *vscsi,
>> 
>> 	switch (virtio32_to_cpu(vscsi->vdev, event->reason)) {
>> 	case VIRTIO_SCSI_EVT_RESET_RESCAN:
>> -		scsi_add_device(shost, 0, target, lun);
>> +		if (lun == 0) {
>> +			scsi_scan_target(&shost->shost_gendev, 0, target,
>> +					 SCAN_WILD_CARD, SCSI_SCAN_INITIAL);
>> +		} else {
>> +			scsi_add_device(shost, 0, target, lun);
>> +		}
>> 		break;
>> 	case VIRTIO_SCSI_EVT_RESET_REMOVED:
>> 		sdev = scsi_device_lookup(shost, 0, target, lun);
>> 
> 
> 
> Acked-by: Paolo Bonzini <pbonzini@redhat.com>

Cc: stable@vger.kernel.org

Thanks, Paolo.

I'm Cc'ing stable as I believe this fixes a driver bug where it
doesn't follow the spec. Per commit message, today devices are
required to issue RESCAN events for each LUN behind a target when
hotplugging, or risking the driver not seeing the new LUNs.

Is this enough? Or should we resend after merge per below?
https://www.kernel.org/doc/Documentation/process/stable-kernel-rules.rst

F.