Re: [PATCH v3] virtio-scsi: Send "REPORTED LUNS CHANGED" sense data upon disk hotplug events.

[Venu Busireddy <venu.busireddy@oracle.com>]

On 2022-09-30 10:41:03 +0200, Paolo Bonzini wrote:
> On Fri, Sep 30, 2022 at 12:31 AM Venu Busireddy
> <venu.busireddy@oracle.com> wrote:
> > > >            */
> > > >           !(buf[0] == REQUEST_SENSE && d->sense_is_ua))) {
> > > >          ops = &reqops_unit_attention;
> > > > +        d->clear_reported_luns_changed = true;
> > >
> > > Any reason to have this flag, and not just clear
> > > s->reported_luns_changed after scsi_req_new? Is it to handle the
> > > invalid opcode case?
> >
> > Immediately after a hotunplug event, qemu (without any action from
> > the guest) processes a REPORT_LUNS command on the lun 0 of the device
> > (haven't figured out what causes this).
> 
> There is only one call to virtio_scsi_handle_cmd_req_prepare and it
> takes the command from the guest, are you sure it is without any
> action from the guest?

I am sure, based on what I am observing. I am running the scsitrace
(scsitrace -n vtioscsi -v) command on the Solaris guest, and I see no
output there. I do see output when I run any scsi related commands (such
as sg_luns, sg_raw, etc) on the guest. But no output when I hotunplug
the disk, either while virtio_scsi_handle_cmd_req_prepare() is running
or after that, until I run any sg_* commands on the guest later.

However, for whatever it's worth, if I have two or more luns
on a virtio-scsi adapter, the spurious REPORT_LUNS processing
(virtio_scsi_handle_cmd_req_prepare() call) occurs only when
I hotunplug a lun while the other luns are still plugged in,
until the last lun is unplugged. I do not see the spurious call to
virtio_scsi_handle_cmd_req_prepare() when the last lun is unplugged,
whether that was the only lun present, or if it was the last of many.

Venu