ftruncate a big file

ftruncate_bigfile.c

#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
#include <sys/stat.h>
#include <time.h>

// Purpose: ftruncate big file
//
// argv[1] file
// argv[2] shrinked size each loop, default is 100m

long current_time() {
    struct timeval t;
    gettimeofday(&t, NULL);
    return t.tv_sec * 1000l + t.tv_usec/ 1000l;
}

int main(int argc, char* argv[]) {
    struct stat st;
    stat(argv[1], &st);
    printf("file size is %ld\n", st.st_size);
    off_t l =  st.st_size;

    off_t shrink_size = 100*1024*1024;
    if (argc == 3)
        shrink_size = atoi(argv[2]);

    off_t shrinked = 0;
    while (l > 0) {
        if (l > shrink_size) {
            l = l - shrink_size;
            shrinked = shrink_size;
        } else {
            shrinked = l;
            l = 0;
        }
        long s1 = current_time();
        truncate(argv[1], l);
        long s2 = current_time();
        printf("--shrinked %ld, now is %ld , spend is %dms --\n", shrinked, l, s2-s1);
        sleep(1);
    }
    return 0;
}