#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>
#include <error.h>
#include <errno.h>
#include <getopt.h>
#include <string.h>
#include <sys/mman.h>

int
main (int argc, char **argv)
{
  int c;
  int fd;
  void *addr;
  int read_write = 0, write_only = 0, private = 0;
  int prot, flags;

  const struct option options[] = {
    { "read-write", no_argument, &read_write, 1 },
    { "write-only", no_argument, &write_only, 1 },
    { "private", no_argument, &private, 1 },
    { NULL, 0, NULL, 0 }
  };

  while (1)
    {
      c = getopt_long (argc, argv, "", options, NULL);
      if (c == '?')
        return EXIT_FAILURE;
      if (c == -1)
        break;
    }

  if (optind != argc - 1)
    error (EXIT_FAILURE, 0, "please specify one file name");

  if (read_write)
    flags = O_RDWR;
  else if (write_only)
    flags = O_WRONLY;
  else
    flags = O_RDONLY;

  fd = open (argv[optind], flags | O_NOCTTY);
  if (fd == -1)
    error (EXIT_FAILURE, errno, "failed to open");

  if (read_write)
    prot = PROT_READ|PROT_WRITE;
  else if (write_only)
    prot = PROT_WRITE;
  else
    prot = PROT_READ;

  flags = MAP_FILE;
  if (private)
    flags |= MAP_PRIVATE;
  else
    flags |= MAP_SHARED;

  addr = mmap (NULL, 4096, prot, flags, fd, 0);
  if (addr == MAP_FAILED)
    error (EXIT_FAILURE, errno, "failed to mmap");

  fprintf (stderr, "mmaped at %p\n", addr);
  fflush (stderr);

  if (!write_only)
    printf ("%s\n", addr);
  if (read_write || write_only)
    strcpy(addr, "well hello friends! :^)\n");

  return 0;
}