Programming

static CSDB_bool fillset(int fd, char* buf, MYSQL_RES* res, int num_chno, int trlen)
{
	//不加参数验证了，必须保证调用正确
	
	
	char* pos		= NULL; //当前位置	
	off_t bottom 	= 0; //映射区起始位置对应的道号，初始为第0道
	int size		= num_chno; //映射区能够容纳的道数
	off_t offset 	= 512;
	size_t bytesize = size * trlen;	//内存映射的大小(含线头)
	size_t sys_page_size = sysconf(_SC_PAGESIZE); //内存页的大小
	int comp		= offset % sys_page_size;	//余数
	offset 			= offset - comp;	//对齐
	
	//初始映射到文件的第一道
	//mmap的最后一个参数真麻烦！！！！
	char* map = (char*)mmap(NULL, bytesize, PROT_READ, MAP_PRIVATE, fd, offset);
	if(map == MAP_FAILED)
	{//映射失败
		perror("mmap()");
		return FALSE;
	}
	//int i = 0;
	//for(i = 0; i < num_chno; ++i)
	MYSQL_ROW row;
	int chno = 0;	
	while((row = mysql_fetch_row(res)))
	{		
		chno = atoi(row[0]);
		if(chno > bottom && chno < bottom + size - 1)
		{		
			pos = map + (chno - bottom) * trlen;
			if(offset == 0)
			{
				memcpy(buf, pos + 512, trlen);	
			}
			else
			{
				memcpy(buf, pos + comp, trlen);	
			}		
					
		}
		else
		{
			offset 	= 512 + (size_t)chno * trlen;
			comp	= offset % sys_page_size;	//余数
			offset 	= offset - comp;	//对齐
			//munmap(map, bytesize);
			//map = (char*)mmap(NULL, bytesize, PROT_READ, MAP_PRIVATE, fd, offset);
			map = (char*)mmap(map, bytesize, PROT_READ, MAP_PRIVATE | MAP_FIXED, fd, offset);
			if(map == MAP_FAILED)
			{
				return FALSE;
			}
			bottom = chno;			
			pos = map;
			if(offset == 0)
			{
				memcpy(buf, pos + 512, trlen);	
			}
			else
			{
				memcpy(buf, pos + comp, trlen);	
			}	
			
		}
		buf = buf + trlen;			
	}
	//卸载映射
	munmap(map, bytesize);
	return TRUE;
}