rem: int write_file(int f,char *buf,int len)
add: int write_file(int f,char *buf,size_t len)
context: int write_file(int f,char *buf,int len){	int ret = 0;	if (!sparse_files) {		return write(f,buf,len);	}	while (len>0) {		int len1 = MIN(len, SPARSE_WRITE_SIZE);		int r1 = write_sparse(f, buf, len1);		if (r1 <= 0) {			if (ret > 0) return ret;			return r1;		}		len -= r1;		buf += r1;		ret += r1;	}	return ret;}