#define _GNU_SOURCE

#include <assert.h>
#include <fcntl.h>
#include <libaio.h>
#include <pthread.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>

// Define this to perform the fallocate and the pwrite sequentially
// instead of in parallel

// #define IN_ORDER


int fd;

void *falloc_thread(void *arg)
{
    int ret;

    (void)arg;

    puts("starting fallocate");

    ret = fallocate(fd, FALLOC_FL_ZERO_RANGE, 0, 4096);
    assert(ret == 0);

    puts("fallocate done");

    return NULL;
}

int main(int argc, char *argv[])
{
    pthread_t falloc_thr;
    int ret;

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

    fd = open(argv[1], O_CREAT | O_RDWR | O_TRUNC | O_DIRECT, 0666);
    assert(fd >= 0);

    void *buf = aligned_alloc(4096, 4096);
    memset(buf, 42, 4096);

    io_context_t ctx = 0;
    ret = io_setup(1, &ctx);
    assert(ret == 0);

    ret = pthread_create(&falloc_thr, NULL, &falloc_thread, NULL);
    assert(ret == 0);

#ifdef IN_ORDER
    ret = pthread_join(falloc_thr, NULL);
    assert(ret == 0);
#endif

    struct iocb ior;
    io_prep_pwrite(&ior, fd, buf, 4096, 4096);

    puts("submitting pwrite");

    struct iocb *ios[] = { &ior };
    ret = io_submit(ctx, 1, ios);
    assert(ret == 1);

    struct io_event evs[1];
    ret = io_getevents(ctx, 1, 1, evs, NULL);
    assert(ret == 1);

    puts("pwrite done");

#ifndef IN_ORDER
    ret = pthread_join(falloc_thr, NULL);
    assert(ret == 0);
#endif

    close(fd);
    free(buf);

    puts("\nHexdump should show 4k of 0s and 4k of 42s:\n");

    execlp("hexdump", "hexdump", "-C", argv[1], NULL);
    return 1;
}