Re: [PATCH v4] virtio-scsi: Send "REPORTED LUNS CHANGED" sense data upon disk hotplug events.

[Mark Kanda <mark.kanda@oracle.com>]

HI Stefano,

On 7/4/2023 9:14 AM, Stefano Garzarella wrote:
> Hi Mark,
> we have a bug [1] possibly related to this patch.
>
> I saw this Oracle Linux errata [2] where you reverted this patch, but
> there are no details.
>
> Do you think we should revert it upstream as well?
> Do you have any details about the problem it causes in Linux?

While the patch fixed an issue with Solaris VMs, we unfortunately discovered 
regressions with hotplug on Linux VMs. The symptoms were similar to what is 
reported in bz2176702. I think reverting it is the right thing to do until this 
can be investigated further.

Thanks/regards,
-Mark

> [1] https://bugzilla.redhat.com/show_bug.cgi?id=2176702
> [2] https://linux.oracle.com/errata/ELSA-2023-12065.html
>
> Thanks,
> Stefano
>
> On Thu, Oct 6, 2022 at 9:53 PM Venu Busireddy <venu.busireddy@oracle.com> wrote:
>> Section 5.6.6.3 of VirtIO specification states, "Events will also
>> be reported via sense codes..." However, no sense data is sent when
>> VIRTIO_SCSI_EVT_RESET_RESCAN or VIRTIO_SCSI_EVT_RESET_REMOVED events
>> are reported (when disk hotplug/hotunplug events occur). SCSI layer
>> on Solaris depends on this sense data, and hence does not handle disk
>> hotplug/hotunplug events.
>>
>> When the disk inventory changes, use the bus unit attention mechanism
>> to return a CHECK_CONDITION status with sense data of 0x06/0x3F/0x0E
>> (sense code REPORTED_LUNS_CHANGED).
>>
>> Signed-off-by: Venu Busireddy <venu.busireddy@oracle.com>
>>
>> v3 -> v4:
>>      - As suggested by Paolo Bonzini, use the bus unit attention mechanism
>>        instead of the device unit attention mechanism.
>>
>> v2 -> v3:
>>      - Implement the suggestion from Paolo Bonzini <pbonzini@redhat.com>.
>>
>> v1 -> v2:
>>      - Send the sense data for VIRTIO_SCSI_EVT_RESET_REMOVED event too.
>> ---
>>   hw/scsi/scsi-bus.c     | 18 ++++++++++++++++++
>>   hw/scsi/virtio-scsi.c  |  2 ++
>>   include/hw/scsi/scsi.h |  1 +
>>   3 files changed, 21 insertions(+)
>>
>> diff --git a/hw/scsi/scsi-bus.c b/hw/scsi/scsi-bus.c
>> index 4403717c4aaf..ceceafb2cdf3 100644
>> --- a/hw/scsi/scsi-bus.c
>> +++ b/hw/scsi/scsi-bus.c
>> @@ -1616,6 +1616,24 @@ static int scsi_ua_precedence(SCSISense sense)
>>       return (sense.asc << 8) | sense.ascq;
>>   }
>>
>> +void scsi_bus_set_ua(SCSIBus *bus, SCSISense sense)
>> +{
>> +    int prec1, prec2;
>> +    if (sense.key != UNIT_ATTENTION) {
>> +        return;
>> +    }
>> +
>> +    /*
>> +     * Override a pre-existing unit attention condition, except for a more
>> +     * important reset condition.
>> +     */
>> +    prec1 = scsi_ua_precedence(bus->unit_attention);
>> +    prec2 = scsi_ua_precedence(sense);
>> +    if (prec2 < prec1) {
>> +        bus->unit_attention = sense;
>> +    }
>> +}
>> +
>>   void scsi_device_set_ua(SCSIDevice *sdev, SCSISense sense)
>>   {
>>       int prec1, prec2;
>> diff --git a/hw/scsi/virtio-scsi.c b/hw/scsi/virtio-scsi.c
>> index 41f2a5630173..cf2721aa46c0 100644
>> --- a/hw/scsi/virtio-scsi.c
>> +++ b/hw/scsi/virtio-scsi.c
>> @@ -956,6 +956,7 @@ static void virtio_scsi_hotplug(HotplugHandler *hotplug_dev, DeviceState *dev,
>>           virtio_scsi_push_event(s, sd,
>>                                  VIRTIO_SCSI_T_TRANSPORT_RESET,
>>                                  VIRTIO_SCSI_EVT_RESET_RESCAN);
>> +        scsi_bus_set_ua(&s->bus, SENSE_CODE(REPORTED_LUNS_CHANGED));
>>           virtio_scsi_release(s);
>>       }
>>   }
>> @@ -973,6 +974,7 @@ static void virtio_scsi_hotunplug(HotplugHandler *hotplug_dev, DeviceState *dev,
>>           virtio_scsi_push_event(s, sd,
>>                                  VIRTIO_SCSI_T_TRANSPORT_RESET,
>>                                  VIRTIO_SCSI_EVT_RESET_REMOVED);
>> +        scsi_bus_set_ua(&s->bus, SENSE_CODE(REPORTED_LUNS_CHANGED));
>>           virtio_scsi_release(s);
>>       }
>>
>> diff --git a/include/hw/scsi/scsi.h b/include/hw/scsi/scsi.h
>> index 001103488c23..3b1b3d278ee8 100644
>> --- a/include/hw/scsi/scsi.h
>> +++ b/include/hw/scsi/scsi.h
>> @@ -186,6 +186,7 @@ SCSIDevice *scsi_bus_legacy_add_drive(SCSIBus *bus, BlockBackend *blk,
>>                                         BlockdevOnError rerror,
>>                                         BlockdevOnError werror,
>>                                         const char *serial, Error **errp);
>> +void scsi_bus_set_ua(SCSIBus *bus, SCSISense sense);
>>   void scsi_bus_legacy_handle_cmdline(SCSIBus *bus);
>>   void scsi_legacy_handle_cmdline(void);
>>
>>