BlockBackend *blk = NULL, *blk_old_backing = NULL, *blk_new_backing = NULL;
uint8_t *buf_old = NULL;
uint8_t *buf_new = NULL;
- BlockDriverState *bs = NULL;
+ BlockDriverState *bs = NULL, *prefix_chain_bs = NULL;
char *filename;
const char *fmt, *cache, *src_cache, *out_basefmt, *out_baseimg;
int c, flags, src_flags, ret;
goto out;
}
+ /*
+ * Find out whether we rebase an image on top of a previous image
+ * in its chain.
+ */
+ prefix_chain_bs = bdrv_find_backing_image(bs, out_real_path);
+
blk_new_backing = blk_new_open(out_real_path, NULL,
options, src_flags, &local_err);
g_free(out_real_path);
continue;
}
+ if (prefix_chain_bs) {
+ /*
+ * If cluster wasn't changed since prefix_chain, we don't need
+ * to take action
+ */
+ ret = bdrv_is_allocated_above(backing_bs(bs), prefix_chain_bs,
+ offset, n, &n);
+ if (ret < 0) {
+ error_report("error while reading image metadata: %s",
+ strerror(-ret));
+ goto out;
+ }
+ if (!ret) {
+ continue;
+ }
+ }
+
/*
* Read old and new backing file and take into consideration that
* backing files may be smaller than the COW image.