#ifndef _GNU_SOURCE
#define _GNU_SOURCE
#endif

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

int main(int argc, char *argv[])
{
    if (argc < 2) {
        fprintf(stderr, "Usage: %s <test file>\n", argv[0]);
        return 1;
    }

    int fd = open(argv[1], O_WRONLY | O_CREAT | O_TRUNC | O_DIRECT | O_APPEND, 0644);
    if (fd < 0) {
        perror("creating test file");
        return 1;
    }

    char *buf = mmap(NULL, 4096, PROT_READ, MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
    ssize_t ret = write(fd, buf, 4096);
    if (ret < 0) {
        perror("pwritev2");
        return 1;
    }

    struct stat stbuf;
    ret = fstat(fd, &stbuf);
    if (ret < 0) {
        perror("stat");
        return 1;
    }

    printf("size: %llu\n", (unsigned long long)stbuf.st_size);
    return stbuf.st_size == 4096 ? 0 : 1;
}