static void qed_copy_from_backing_file(BDRVQEDState *s, uint64_t pos,

                                       uint64_t len, uint64_t offset,

                                       BlockDriverCompletionFunc *cb,

                                       void *opaque)

{

    CopyFromBackingFileCB *copy_cb;



    /* Skip copy entirely if there is no work to do */

    if (len == 0) {

        cb(opaque, 0);

        return;

    }



    copy_cb = gencb_alloc(sizeof(*copy_cb), cb, opaque);

    copy_cb->s = s;

    copy_cb->offset = offset;

    copy_cb->iov.iov_base = qemu_blockalign(s->bs, len);

    copy_cb->iov.iov_len = len;

    qemu_iovec_init_external(&copy_cb->qiov, &copy_cb->iov, 1);



    qed_read_backing_file(s, pos, &copy_cb->qiov,

                          qed_copy_from_backing_file_write, copy_cb);

}
