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

int main(int argc, char *argv[])
{
    if (argc != 3) {
        fprintf(stderr, "usage: %s from_file to_file", argv[0]);
        exit(0);
    }

    /* from */
    int from = open(argv[1], O_RDONLY, 0644);
    assert(from >= 0);

    struct stat st_buf;
    assert(fstat(from, &st_buf) >= 0);
    size_t size = st_buf.st_size;

    void *from_mmap = mmap(NULL, size, PROT_READ, MAP_SHARED, from, 0);
    assert(from_mmap >= 0);

#if USE_MADVISE
    assert(madvise(from_mmap, size, MADV_SEQUENTIAL) >= 0);
#endif

    /* to */
    int to = open(argv[2], O_CREAT | O_WRONLY, 0666);
    assert(to >= 0);

    /* copy */
    char *p = from_mmap;
    const char * const endp = from_mmap + size;
    while (p < endp) {
        int num_bytes = write(to, p, endp - p);
        p += num_bytes;
    }
    assert(p == endp);

    fsync(to);

    close(to);
    close(from);

    return 0;
}