Pass the drive's readonly attribute to the guest OS

Implemented for virtio-blk and for scsi
Signed-off-by: NNaphtali Sprei <nsprei@redhat.com>
Signed-off-by: NAnthony Liguori <aliguori@us.ibm.com>

hw/scsi-disk.c

@@ -633,7 +633,8 @@ static int32_t scsi_send_command(SCSIDevice *d, uint32_t tag,
             memset(p, 0, 4);
             outbuf[1] = 0; /* Default media type.  */
             outbuf[3] = 0; /* Block descriptor length.  */
-            if (bdrv_get_type_hint(s->dinfo->bdrv) == BDRV_TYPE_CDROM) {
+            if (bdrv_get_type_hint(s->dinfo->bdrv) == BDRV_TYPE_CDROM ||
+                bdrv_is_read_only(s->dinfo->bdrv)) {
                 outbuf[2] = 0x80; /* Readonly.  */
             }
             p += 4;

hw/virtio-blk.c

@@ -444,6 +444,9 @@ static uint32_t virtio_blk_get_features(VirtIODevice *vdev)
 #endif
     if (strcmp(s->serial_str, "0"))
         features |= 1 << VIRTIO_BLK_F_IDENTIFY;
+    
+    if (bdrv_is_read_only(s->bs))
+        features |= 1 << VIRTIO_BLK_F_RO;
 
     return features;
 }