mmap problem with vboxfs

mmap-problem.c

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

int main (int argc, char *argv[])
{
  struct stat sb;
  off_t len;
  char *p;
  int fd;

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

  fd = open (argv[1], O_RDWR, S_IRUSR | S_IWUSR);
  if (fd == -1) {
    perror ("open");
    return 1;
  }

  if (fstat (fd, &sb) == -1) {
    perror ("fstat");
    return 1;
  }

  if (!S_ISREG (sb.st_mode)) {
    fprintf (stderr, "%s is not a file\n", argv[1]);
    return 1;
  }

  p = mmap (0, sb.st_size, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);
  if (p == MAP_FAILED) {
    perror ("mmap");
    return 1; 
  }

  if (close (fd) == -1) {
    perror ("close");
    return 1; 
  }

  for (len = 0; len < sb.st_size; len++)
    putchar (p[len]);

  if (munmap (p, sb.st_size) == -1) {
    perror ("munmap");
    return 1; 
  }

  return 0;
}