guestfs_set_reply_callback (g, blockdev_getsize64_reply_cb, &ctx);
(void) ml->main_loop_run (ml, g);
guestfs_set_reply_callback (g, NULL, NULL);
guestfs_set_reply_callback (g, blockdev_getsize64_reply_cb, &ctx);
(void) ml->main_loop_run (ml, g);
guestfs_set_reply_callback (g, NULL, NULL);