/*
 * See https://fedoraproject.org/wiki/QA:Testcase_Virtualization_XenDomU_Save_and_restore
 */

#include <errno.h>
#include <fcntl.h>
#include <stdio.h>
#include <string.h>
#include <unistd.h>

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

#define DEVICE "/dev/zero"
#define REGION_SIZE 16*1024*1024

int main(void)
{
  int fd;
  void *mem, *lastmem = NULL;

  fd = open(DEVICE, O_RDONLY);
  if ( fd == -1 )
    {
      fprintf(stderr, "failed to open " DEVICE ": %s\n", strerror(errno));
      return 1;
    }

  while (1)
    {
      mem = mmap(0, REGION_SIZE, PROT_READ, MAP_PRIVATE, fd, 0);
      if ( mem == MAP_FAILED )
        {
          fprintf(stderr, "failed to mmap region: %s\n", strerror(errno));
          return 1;
        }

      if ( mprotect(mem, REGION_SIZE, PROT_NONE) < 0 )
        {
          fprintf(stderr, "failed to mprotect region: %s\n", strerror(errno));
          return 1;
        }
      printf("mapped PROT_NONE region at %p.\n", mem);

      /*
       * Unmap previous region after mapping the next so
       * there is always at least one PROT_NONE region
       * mapped.
       *
       * If the kernel does not correctly handle non-present
       * PTEs then it will crash on unmap.
       */
      if ( lastmem != NULL )
        {
          if ( munmap(lastmem, REGION_SIZE) < 0 )
            {
              fprintf(stderr, "failed to unmap region: %s\n", strerror(errno));
              return 1;
            }

          printf("unmapped PROT_NONE region at %p.\n", lastmem);
        }

      lastmem = mem;

      sleep(1);
    }

  return 0;
}