int qcow2_backing_read1(BlockDriverState *bs, QEMUIOVector *qiov, int64_t sector_num, int nb_sectors) { int n1; if ((sector_num + nb_sectors) <= bs->total_sectors) return nb_sectors; if (sector_num >= bs->total_sectors) n1 = 0; else n1 = bs->total_sectors - sector_num; qemu_iovec_memset(qiov, 0, 512 * (nb_sectors - n1)); return n1; }