scsi-block: always use scsi_generic_ops for cache != none

Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

hw/scsi-disk.c

@@ -1754,6 +1754,15 @@ static SCSIRequest *scsi_block_new_request(SCSIDevice *d, uint32_t tag,
     case WRITE_VERIFY_10:
     case WRITE_VERIFY_12:
     case WRITE_VERIFY_16:
+        /* If we are not using O_DIRECT, we might read stale data from the
+	 * host cache if writes were made using other commands than these
+	 * ones (such as WRITE SAME or EXTENDED COPY, etc.).  So, without
+	 * O_DIRECT everything must go through SG_IO.
+         */
+        if (!(s->qdev.conf.bs->open_flags & BDRV_O_NOCACHE)) {
+            break;
+        }
+
         /* MMC writing cannot be done via pread/pwrite, because it sometimes
          * involves writing beyond the maximum LBA or to negative LBA (lead-in).
          * And once you do these writes, reading from the block device is
@@ -1764,10 +1773,11 @@ static SCSIRequest *scsi_block_new_request(SCSIDevice *d, uint32_t tag,
          * seen, but performance usually isn't paramount on optical media.  So,
          * just make scsi-block operate the same as scsi-generic for them.
          */
-        if (s->qdev.type != TYPE_ROM) {
-            return scsi_req_alloc(&scsi_disk_reqops, &s->qdev, tag, lun,
-                                  hba_private);
-        }
+        if (s->qdev.type == TYPE_ROM) {
+            break;
+	}
+        return scsi_req_alloc(&scsi_disk_reqops, &s->qdev, tag, lun,
+                              hba_private);
     }
 
     return scsi_req_alloc(&scsi_generic_req_ops, &s->qdev, tag, lun,