iscsi: send readcapacity10 when readcapacity16 failed

When play with Dell MD3000 target, for sure it
is a TYPE_DISK, but readcapacity16 would fail.
Then we find that readcapacity10 succeeded. It
looks like the target just support readcapacity10
even through it is a TYPE_DISK or have some
TYPE_ROM characteristics.

This patch can give a chance to send
readcapacity16 when readcapacity10 failed.
This patch is not harmful to original pathes

Signed-off-by: Zhu Lingshan <lszhu@suse.com>
Message-Id: <1451359934-9236-1-git-send-email-lszhu@suse.com>
[Don't fall through on UNIT ATTENTION. - Paolo]
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

block/iscsi.c

@@ -1243,8 +1243,13 @@ static void iscsi_readcapacity_sync(IscsiLun *iscsilun, Error **errp)
                     iscsilun->lbprz = !!rc16->lbprz;
                     iscsilun->use_16_for_rw = (rc16->returned_lba > 0xffffffff);
                 }
+                break;
             }
-            break;
+            if (task != NULL && task->status == SCSI_STATUS_CHECK_CONDITION
+                && task->sense.key == SCSI_SENSE_UNIT_ATTENTION) {
+                break;
+            }
+            /* Fall through and try READ CAPACITY(10) instead.  */
         case TYPE_ROM:
             task = iscsi_readcapacity10_sync(iscsilun->iscsi, iscsilun->lun, 0, 0);
             if (task != NULL && task->status == SCSI_STATUS_GOOD) {