Linux下快速拷贝单个大文件的秘诀

上代码

#include <stdio.h>
#include <unistd.h>
#include <fcntl.h>
#include <stdlib.h>
#include <string.h>
#include <sys/mman.h>
#include <sys/stat.h>
#include <sys/wait.h>
 
void err_int(int ret, const char *err)
{
    if (ret == -1) {
        perror(err);
        exit(1);
    }
 
    return ;
}
 
void err_str(char *ret, const char *err)
{
    if (ret == MAP_FAILED) {
        perror(err);
        exit(1);
    }
}
 
int main(int argc, char *argv[])
{   
    int fd_src, fd_dst, ret, len, i, n;
    char *mp_src, *mp_dst, *tmp_srcp, *tmp_dstp;
    pid_t pid;
    struct stat sbuf;
 
    if (argc < 3 || argc > 4) {
        printf("使用方法: ./script src_file dest_file
");
        printf("例子: ./copy a.file /vdb/a.file
");
        exit(1);
    } else if (argc == 3) {
        n = 5;
    } else if (argc == 4) {
        n = atoi(argv[3]);
    }
 
    fd_src = open(argv[1], O_RDONLY);
    err_int(fd_src, "open dict.txt err");
    fd_dst = open(argv[2], O_RDWR | O_CREAT | O_TRUNC, 0664);
    err_int(fd_dst, "open dict.cp err");
    ret = fstat(fd_src, &sbuf);
    err_int(ret, "fstat err");
    
    len = sbuf.st_size;
    if (len < n) 
        n = len;
    ret = ftruncate(fd_dst, len);
    err_int(ret, "truncate fd_dst err");
    mp_src = (char *)mmap(NULL, len, PROT_READ, MAP_SHARED, fd_src, 0);
    err_str(mp_src, "mmap src err");
    mp_dst = (char *)mmap(NULL, len, PROT_READ | PROT_WRITE, MAP_SHARED, fd_dst, 0);
    err_str(mp_dst, "mmap dst err");
 
    tmp_dstp = mp_dst;
    tmp_srcp = mp_src;
    int bs = len / n;
    int mod = len % bs; 
 
    for (i = 0; i < n; i++) {
        if ((pid = fork()) == 0) {
            break;
        }
    }
 
    if (n == i) { 
        for (i = 0; i < n; i++)
            wait(NULL);
 
    } else if (i == (n-1)){
        memcpy(tmp_dstp+i*bs, tmp_srcp+i*bs, bs+mod); 
    } else if (i == 0) {
        memcpy(tmp_dstp, tmp_srcp, bs); 
    } else {
        memcpy(tmp_dstp+i*bs, tmp_srcp+i*bs, bs); 
    }
 
    munmap(mp_src, len);
    munmap(mp_dst, len);
 
    return 0;
}

将上面文件保存为copy.c，使用方式：

gcc copy.c -o copy

./copy src_file dest/src_file

会发现速度超级快