static int cow_create(const char *filename, QemuOpts *opts, Error **errp) { struct cow_header_v2 cow_header; struct stat st; int64_t image_sectors = 0; char *image_filename = NULL; Error *local_err = NULL; int ret; BlockDriverState *cow_bs; /* Read out options */ image_sectors = qemu_opt_get_size_del(opts, BLOCK_OPT_SIZE, 0) / 512; image_filename = qemu_opt_get_del(opts, BLOCK_OPT_BACKING_FILE); ret = bdrv_create_file(filename, opts, &local_err); if (ret < 0) { error_propagate(errp, local_err); goto exit; } cow_bs = NULL; ret = bdrv_open(&cow_bs, filename, NULL, NULL, BDRV_O_RDWR | BDRV_O_PROTOCOL, NULL, &local_err); if (ret < 0) { error_propagate(errp, local_err); goto exit; } memset(&cow_header, 0, sizeof(cow_header)); cow_header.magic = cpu_to_be32(COW_MAGIC); cow_header.version = cpu_to_be32(COW_VERSION); if (image_filename) { /* Note: if no file, we put a dummy mtime */ cow_header.mtime = cpu_to_be32(0); if (stat(image_filename, &st) != 0) { goto mtime_fail; } cow_header.mtime = cpu_to_be32(st.st_mtime); mtime_fail: pstrcpy(cow_header.backing_file, sizeof(cow_header.backing_file), image_filename); } cow_header.sectorsize = cpu_to_be32(512); cow_header.size = cpu_to_be64(image_sectors * 512); ret = bdrv_pwrite(cow_bs, 0, &cow_header, sizeof(cow_header)); if (ret < 0) { goto exit; } /* resize to include at least all the bitmap */ ret = bdrv_truncate(cow_bs, sizeof(cow_header) + ((image_sectors + 7) >> 3)); if (ret < 0) { goto exit; } exit: g_free(image_filename); bdrv_unref(cow_bs); return ret; }