我想打开一个大小为100GB的文件,每次都使用文件映射来从块中读取数据块。当偏移量大于2GB时,它总是会开始映射。我以为我可能是不支持64位寻址的功能。但是在我添加大文件支持(包括大文件支持定义,大文件打开选项,以及使用命令-D_FILE_OFFSET_BITS = 64 -D_LARGE_FILE编译)之后。但是,仍然会出现同样的问题。这是简化的代码:
#define _LARGEFILE_SOURCE
#define _LARGEFILE64_SOURCE
#define _FILE_OFFSET_BITS 64
#include <math.h>
#include <time.h>
#include <errno.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include<fcntl.h>
#include<unistd.h>
#include<sys/stat.h>
#include<sys/time.h>
#include<sys/mman.h>
#include<sys/types.h>
#define PERMS 0600
int total_piece, PAGE, buffer, share, offset, count, chunk;
void get_size(char * strFileName)
{
struct stat temp;
stat(strFileName, &temp);
PAGE = getpagesize();
total_piece = temp.st_size/PAGE;
chunk = 1024*1024*1024*0.4/PAGE;
if (temp.st_size%PAGE!=0)
total_piece++;
}
char *
mmaping (char *source)
{
int src;
char *sm;
struct stat statbuf;
if ((src = open (source, O_RDONLY)) < 0) //I thought error comes from this line. So I tried to use large file support as following. But still the same.
{
perror (" open source ");
exit (EXIT_FAILURE);
}
/*
if ((src = open64(source, O_RDONLY|O_LARGEFILE, 0644))<0)
{
perror (" open source ");
exit (EXIT_FAILURE);
}
*/
if (fstat (src, &statbuf) < 0)
{
perror (" fstat source ");
exit (EXIT_FAILURE);
}
printf("share->%d PAGES per node\n",share);
if (share>=chunk)
buffer = chunk;
else
buffer = share;
printf("total pieces->%d\n",total_piece);
printf("data left->%d\n",share);
printf("buffer size->%d\n",buffer);
printf("PAGE size->%d\n",PAGE);
sm = mmap (0,buffer*PAGE, PROT_READ, MAP_SHARED | MAP_NORESERVE,src, offset*PAGE);
if (MAP_FAILED == sm)
{
perror (" mmap source ");
exit (EXIT_FAILURE);
}
return sm;
}
main(int argc, char**argv){
get_size(argv[1]);
share = total_piece;
offset = 0;
while (share>0)
{
char *x = mmaping(argv[1]);
printf("data->%0.30s\n",x); //bus error will occur when offset reaches 2GiB, which proves my thought: it maps nothing.
munmap(x,buffer*PAGE);
share-=buffer;
offset+=buffer;
}
return 0;
}
有人可以帮助我吗?
答案 0 :(得分:5)
当然,类型为&#34; int&#34;的变量,在Linux上为32位,不足以包含100 GB文件的字节大小。对于文件大小/偏移量,您需要使用类型&#34; off_t&#34;相反(当你已经完成启用LFS支持时,它是off64_t的一个别名,一个带符号的64位整数)。
同样,&#34;长度&#34; mmap的参数是size_t类型,而不是int。
为了使代码可以同时移植到32位和64位目标,无论是否有LFS,您都需要注意应该在哪里使用哪些整数类型。