+ if (has_replaces) {
+ BlockDriverState *to_replace_bs;
+ AioContext *replace_aio_context;
+ int64_t bs_size, replace_size;
+
+ bs_size = bdrv_getlength(bs);
+ if (bs_size < 0) {
+ error_setg_errno(errp, -bs_size, "Failed to query device's size");
+ return;
+ }
+
+ to_replace_bs = check_to_replace_node(bs, replaces, errp);
+ if (!to_replace_bs) {
+ return;
+ }
+
+ replace_aio_context = bdrv_get_aio_context(to_replace_bs);
+ aio_context_acquire(replace_aio_context);
+ replace_size = bdrv_getlength(to_replace_bs);
+ aio_context_release(replace_aio_context);
+
+ if (replace_size < 0) {
+ error_setg_errno(errp, -replace_size,
+ "Failed to query the replacement node's size");
+ return;
+ }
+ if (bs_size != replace_size) {
+ error_setg(errp, "cannot replace image with a mirror image of "
+ "different size");
+ return;
+ }
+ }
+