#define _GNU_SOURCE
#include <sys/mman.h>
#include <sys/resource.h>
#include <errno.h>
#include <limits.h>
#include <malloc.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>

#define PAGE_SIZE 4096
// NOTE: DATA=MAP2=16 seems to trigger in the first few tries
// NOTE: 9/9 needs a loop and a few seconds to trigger
// NOTE: DATA=9, MAP2=8 does not trigger
#define DATA_SIZE 16
#define MAP2_SIZE 16

int shmfd;
char shmpath[] = "/dev/shm/mmaptest-XXXXXX";
unsigned char *map1, *map2;
unsigned int i;

int main(int argc, char *argv[]) {
  /* create a data file on tmpfs */
  shmfd = mkstemp(shmpath);
  if (shmfd < 0) {
    perror("mkstemp");
    exit(2);
  }

  if (unlink(shmpath)) {
    perror("unlink");
    exit(2);
  }

  if (ftruncate(shmfd, DATA_SIZE * PAGE_SIZE)) {
    perror("ftruncate");
    exit(2);
  }

  /* map a single page from the file */
  map1 = mmap(NULL, PAGE_SIZE, PROT_READ | PROT_WRITE, MAP_SHARED, shmfd, 0);
  if (map1 == MAP_FAILED) {
    perror("mmap 1");
    exit(2);
  }

  /* remap it to another page in the file */
  // NOTE: Does not trigger without remapping
  // NOTE: Does not trigger for 7, but does trigger for 8 if both sizes are 16
  //  (DATA_SIZE-2 is sufficiently generic here)
  if (remap_file_pages(map1, PAGE_SIZE, 0, DATA_SIZE - 2, MAP_SHARED)) {
    perror("remap_file_pages 1");
    exit(2);
  }

  /* create a second mapping */
  map2 = mmap(NULL, MAP2_SIZE * PAGE_SIZE, PROT_READ | PROT_WRITE,
              MAP_SHARED, shmfd, 0);
  if (map2 == MAP_FAILED) {
    perror("mmap 2");
    exit(2);
  }

  /* map all of its pages to page 0 */
  // NOTE: Remapping only the last page does not trigger
  for (i = 0; i < MAP2_SIZE; i++) {
    if (remap_file_pages(map2 + PAGE_SIZE * i, PAGE_SIZE, 0, 0, MAP_SHARED)) {
      perror("remap_file_pages 3");
      exit(2);
    }
  }

  close(shmfd);

  exit(0);
}