[Qemu-devel] Re: [PATCH v2 1/2] cdrom: Allow the TEST_UNIT_READY command after a cdrom change

[Amit Shah <amit.shah@redhat.com>]

On (Thu) 07 Apr 2011 [10:59:20], Kevin Wolf wrote:
> Am 07.04.2011 07:05, schrieb Amit Shah:
> > We restrict the commands that a guest can send us after a cdrom change
> > event.  The current list includes REQUEST_SENSE and INQUIRY commands.
> > Guests can also issue TEST_UNIT_READY to inquire for the status, so
> > allow this command as well.
> > 
> > Signed-off-by: Amit Shah <amit.shah@redhat.com>
> 
> Hm... MMC-5, section 4.1.6.1 seems to conflict with this:
> 
> "If a Host issues a command other than GET CONFIGURATION, GET EVENT
> STATUS NOTIFICATION, INQUIRY or REQUEST SENSE while a unit attention
> condition exists for that Host, the Drive shall not perform the command
> and shall report CHECK CONDITION status unless a higher priority status
> as defined by the Drive is also pending."
> 
> So while you're right that our list is incomplete, TEST UNIT READY
> doesn't seem to be among the missing commands.

Hm - older Linux guests (pre 2.6.38) and Windows guests, as Gleb's
commit mentioned, rely on this command to get CD change notifications:

/* identical to scsi_test_unit_ready except that it doesn't
 * eat the NOT_READY returns for removable media */
int sr_test_unit_ready(struct scsi_device *sdev, struct scsi_sense_hdr *sshdr)
{
        int retries = MAX_RETRIES;
        int the_result;
        u8 cmd[] = {TEST_UNIT_READY, 0, 0, 0, 0, 0 };

        /* issue TEST_UNIT_READY until the initial startup UNIT_ATTENTION
         * conditions are gone, or a timeout happens
         */
        do {
                the_result = scsi_execute_req(sdev, cmd, DMA_NONE, NULL,
                                              0, sshdr, SR_TIMEOUT,
                                              retries--, NULL);
                if (scsi_sense_valid(sshdr) &&
                    sshdr->sense_key == UNIT_ATTENTION)
                        sdev->changed = 1;

        } while (retries > 0 &&
                 (!scsi_status_is_good(the_result) ||
                  (scsi_sense_valid(sshdr) &&
                   sshdr->sense_key == UNIT_ATTENTION)));
        return the_result;
}


There could be something else brewing as well.  We never report a
'tray open' condition; maybe the guest will be happy with such a thing
as well.  Will have to check.

		Amit