使用mmap實現檔案的拷貝

mmap與munmap函式介紹：

#include #include void *mmap(void *start, size_t length, int prot, int flag, int fd, off_t offset);

//返回:若成功時則返回對映區域的指標，若出錯則為map_failed(-1)

length: 對映區域的大小

prot: 對映區域的訪問許可權位 prot_exec prot_read prot_write prot_none

flags: 對映物件的型別 map_anon map_private map_shared

munmap函式刪除對映區域

#include #include int munmap(void *start, size_t length);

分別使用了mmap函式和普通的read write實現了檔案的複製拷貝，下面是通過複製50m的檔案效能分析：

[yangguang@sim124 ~]$ time ./workspace/mmapcopy linux-20101214.tar.gz ./output    

real 0m0.100s
user 0m0.034s
sys 0m0.065s

[yangguang@sim124 ~]$ time ./workspace/copy linux-20101214.tar.gz ./output

real 0m5.016s
user 0m0.000s
sys 0m0.124s

可以看到使用mmap的效能明顯高於使用read write的方式，這裡主要原因是使用mmap減少了使用者態和核心態間資料

的拷貝。

原始碼分析

/*

* author: liyangguang * 
* * file: mmapcopy.c
* create date: 2011-07-04 21:02:48
* */
#include #include #include #include #include #include #include #include void
mmapcopy(int src_fd, size_t src_len, int dst_fd)
memcpy(dst_ptr, src_ptr, src_len);
munmap(src_ptr, src_len);
munmap(dst_ptr, src_len);} 
int 
main(int argc, char* argv)
int src_fd = open(argv[1], o_rdonly);
int dst_fd = open(argv[2], o_rdwr | o_creat | o_trunc);;
struct stat stat;
fstat(src_fd, &stat);
truncate(argv[2], stat.st_size);
mmapcopy(src_fd, stat.st_size, dst_fd);
close(src_fd);
close(dst_fd);
return 0;
}

/*

* author: liyangguang * 
* * file: copy.c
* create date: 2011-07-04 21:38:00
* */
#include #include #include #include #include #include #include void
copy(int src_fd, int dst_fd)
ptr = buffer;
} }int 
main(int argc, char* argv)
int src_fd = open(argv[1], o_rdonly);
int dst_fd = open(argv[2], o_rdwr | o_creat | o_trunc, s_irwxu);;
copy(src_fd, dst_fd);
close(src_fd);
close(dst_fd);
return 0;} 
/* vim: set ts=4 sw=4: */

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