#define _GNU_SOURCE
#include <pthread.h>
#include <err.h>
#include <stdarg.h>
#include <stdio.h>
#include <stdlib.h>
#include <poll.h>
#include <unistd.h>
#include <sys/mman.h>
#include <sys/prctl.h>
#include <sys/eventfd.h>
#include <sys/syscall.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <netinet/tcp.h>
#include <linux/io_uring.h>

#define SYSCHK(x) ({          \
  typeof(x) __res = (x);      \
  if (__res == (typeof(x))-1) \
    err(1, "SYSCHK(" #x ")"); \
  __res;                      \
})

#define NUM_SQ_PAGES 4

static int uring_fd;
static struct io_uring_sqe *sq_data;

static void *thread_fn(void *dummy) {
  sleep(1);
  sq_data->cmd_op = 0x5678;
  return NULL;
}

int main(void) {
  printf("main pid: %d\n", getpid());

  // sq
  sq_data = SYSCHK(mmap(NULL, NUM_SQ_PAGES*0x1000, PROT_READ|PROT_WRITE, MAP_SHARED|MAP_ANONYMOUS, -1, 0));
  // cq
  void *cq_data = SYSCHK(mmap(NULL, NUM_SQ_PAGES*0x1000, PROT_READ|PROT_WRITE, MAP_SHARED|MAP_ANONYMOUS, -1, 0));
  *(volatile unsigned int *)(cq_data+4) = 64 * NUM_SQ_PAGES;

  // initialize uring
  struct io_uring_params params = {
    .flags = IORING_SETUP_DEFER_TASKRUN|IORING_SETUP_SINGLE_ISSUER|IORING_SETUP_NO_MMAP|IORING_SETUP_NO_SQARRAY,
    .sq_off = { .user_addr = (unsigned long)sq_data },
    .cq_off = { .user_addr = (unsigned long)cq_data }
  };
  uring_fd = SYSCHK(syscall(__NR_io_uring_setup, /*entries=*/10, &params));

  int sockfd = SYSCHK(socket(AF_INET, SOCK_STREAM, 0));

  sq_data[0] = (struct io_uring_sqe) {
    .opcode = IORING_OP_URING_CMD,
    .flags = 0,
    .ioprio = 0,
    .fd = sockfd,
    .cmd_op = 0x1234,
    .user_data = 123
  };

  pthread_t thread;
  if (pthread_create(&thread, NULL, thread_fn, NULL))
    errx(1, "pthread_create");

  int submitted = SYSCHK(syscall(__NR_io_uring_enter, uring_fd,
                                 /*to_submit=*/1, /*min_complete=*/1,
                                 /*flags=*/IORING_ENTER_GETEVENTS, /*sig=*/NULL, /*sigsz=*/0));
  printf("submitted %d\n", submitted);
  return 0;
}