mmap 错误

int readlen = 5*1024*1024;
//int readlen = 1024;
int fd = open("/home/bonc/BC000D0300420131210000001.AVL",O_RDONLY);
//int fd = open("/home/bonc/ds.ini",O_RDONLY);
int len = lseek(fd,0,SEEK_END);


//if(!file)
//		printf("can not open file!\n");
std::string s;

int start = time(NULL);
int offset = 0;
	//while(getline(file, s))
while(len > 0)
{
		if(len <= readlen)
			readlen = len;
		char *mbuf = (char *)mmap(NULL, readlen, PROT_READ, MAP_PRIVATE, fd, offset);
		if(MAP_FAILED == mbuf)
		{
			perror("mbuf can not get address!\n");
			break;
		}
		int pos = 0;
		int start  = 0;
		while(pos < readlen)
		{
			if(*(mbuf + pos) != '\n')
			{
				s.append((const char*)(mbuf + pos), 1);
				pos++;
			}
			else
			{
				//s.assign(mbuf + start, pos - start);
				//cout << s << endl;
				s = "";
				pos++;
				//start = pos;
			}
		}
		offset += readlen;
		len -= readlen;
		munmap( mbuf, readlen );//解除映射关系
		//msync ( mbuf , readlen, MS_SYNC);//更新文件
		//cout << s << endl;
	}


	int end = time(NULL);
	printf("it takes %d seconds\n", end-start);
	return 0;
           

上述代码 主要用途 分段映射大文件（代码比较糙

，主要问了记录下述错误）；

注意问题 ：mmap 最后一个参数 必须为页大小的倍数 ，否则报错：Invalid Argument；