#include <sys/stat.h>
#include <sys/fcntl.h>
#include <sys/mman.h>
#include <fcntl.h>
#include <unistd.h>
#include <stdio.h>
#include <string.h>
#include <assert.h>

int main(int argc, char *argv[])
{
    int fin;
    struct stat st;

    if (argc != 2)
    {
        fprintf(stderr, "Usage: %s <file>\n", argv[0]);
        return 1;
    }

    fin = open(argv[1], O_RDWR);
    assert(fin >= 0);

    fstat(fin, &st);

    if (st.st_nlink > 1)
    {
        unlink(argv[1]);
        close(fin);
        return 0;
    }

    char *src = mmap(NULL, st.st_size, PROT_WRITE, MAP_SHARED, fin, 0);
    assert(src != MAP_FAILED);

    memset(src, 0xff, st.st_size);

    munmap(src, st.st_size);
    src = mmap(NULL, st.st_size, PROT_WRITE, MAP_SHARED, fin, 0);
    assert(src != MAP_FAILED);

    int urandom = open("/dev/urandom", O_RDONLY);
    assert(urandom >= 0);

    ssize_t r = read(urandom, src, st.st_size);
    assert(r == st.st_size);

    munmap(src, st.st_size);

    char new_name[64];
    r = read(urandom, new_name, sizeof(new_name));
    assert(r == sizeof(new_name));

    close(urandom);
    close(fin);

    rename(argv[1], new_name);
    remove(new_name);
}