#define _GNU_SOURCE

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

#include <stdio.h>
#include <string.h>

/*
 * the 'abusive' case is where we
 *   grow the file via pwrite
 *   unmap the previous mapping,
 *   do the new mapping
 *
 * the non-abusive case we
 *   unmap the previous mapping
 *   grow the file
 *   do the new mapping
 *
 * the difference being that in the abusive case,
 * we maintain a mapping during the pwrite.
 *
 * If we grow the file via pwrite and maintain a
 * mapping, the mapped pages are never written out.
 *
 * If we either grow the file via ftruncate or remove
 * old mappings before growing the file, then all is
 * fine.
 */

#ifdef ABUSE
#define UNMAP_AFTER() munmap(mapping, size)
#define UNMAP_BEFORE() struct eat_semi
#else
#define UNMAP_AFTER() struct eat_semi
#define UNMAP_BEFORE() munmap(mapping, size)
#endif

int main(int argc, char* argv[])
{
  int fd;
  unsigned int const size = 4096 * 1024;
  unsigned int offset = 0;

  if (argc != 2) {
    printf("usage: %s <filename>\n", argv[0]);
    return 0;
  }

  fd = open(argv[1], O_RDWR | O_CREAT | O_TRUNC | O_LARGEFILE | O_DIRECT, 0644);
  if (fd < 0) {
    perror("open");
    return 0;
  }

  pwrite64(fd, "", 1, offset + size);
  //ftruncate64(fd, offset + size);
  char* mapping = (char*)mmap64(0, size, PROT_READ | PROT_WRITE, MAP_SHARED, fd, offset);
  memset(mapping, 'a', size);
  UNMAP_BEFORE();

  for (;;) {
    offset += size;

    pwrite64(fd, "", 1, offset + size);
    //ftruncate64(fd, offset + size);
    UNMAP_AFTER();
    mapping = (char*)mmap64(0, size, PROT_READ | PROT_WRITE, MAP_SHARED, fd, offset);
    memset(mapping, 'a', size);
    UNMAP_BEFORE();
  }

  close(fd);

  return 0;
}