+void block_copy_set_copy_opts(BlockCopyState *s, bool use_copy_range,
+ bool compress)
+{
+ /* Keep BDRV_REQ_SERIALISING set (or not set) in block_copy_state_new() */
+ s->write_flags = (s->write_flags & BDRV_REQ_SERIALISING) |
+ (compress ? BDRV_REQ_WRITE_COMPRESSED : 0);
+
+ if (s->max_transfer < s->cluster_size) {
+ /*
+ * copy_range does not respect max_transfer. We don't want to bother
+ * with requests smaller than block-copy cluster size, so fallback to
+ * buffered copying (read and write respect max_transfer on their
+ * behalf).
+ */
+ s->method = COPY_READ_WRITE_CLUSTER;
+ } else if (compress) {
+ /* Compression supports only cluster-size writes and no copy-range. */
+ s->method = COPY_READ_WRITE_CLUSTER;
+ } else {
+ /*
+ * If copy range enabled, start with COPY_RANGE_SMALL, until first
+ * successful copy_range (look at block_copy_do_copy).
+ */
+ s->method = use_copy_range ? COPY_RANGE_SMALL : COPY_READ_WRITE;
+ }
+}
+
+static int64_t block_copy_calculate_cluster_size(BlockDriverState *target,
+ Error **errp)
+{
+ int ret;
+ BlockDriverInfo bdi;
+ bool target_does_cow = bdrv_backing_chain_next(target);
+
+ /*
+ * If there is no backing file on the target, we cannot rely on COW if our
+ * backup cluster size is smaller than the target cluster size. Even for
+ * targets with a backing file, try to avoid COW if possible.
+ */
+ ret = bdrv_get_info(target, &bdi);
+ if (ret == -ENOTSUP && !target_does_cow) {
+ /* Cluster size is not defined */
+ warn_report("The target block device doesn't provide "
+ "information about the block size and it doesn't have a "
+ "backing file. The default block size of %u bytes is "
+ "used. If the actual block size of the target exceeds "
+ "this default, the backup may be unusable",
+ BLOCK_COPY_CLUSTER_SIZE_DEFAULT);
+ return BLOCK_COPY_CLUSTER_SIZE_DEFAULT;
+ } else if (ret < 0 && !target_does_cow) {
+ error_setg_errno(errp, -ret,
+ "Couldn't determine the cluster size of the target image, "
+ "which has no backing file");
+ error_append_hint(errp,
+ "Aborting, since this may create an unusable destination image\n");
+ return ret;
+ } else if (ret < 0 && target_does_cow) {
+ /* Not fatal; just trudge on ahead. */
+ return BLOCK_COPY_CLUSTER_SIZE_DEFAULT;
+ }
+
+ return MAX(BLOCK_COPY_CLUSTER_SIZE_DEFAULT, bdi.cluster_size);
+}
+