#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>
#include <sys/mman.h>
#include <assert.h>
#include <errno.h>
#include <string.h>


#define BUFFER_SIZE (1024)

int main (int argc, char *argv[])
{
  int file_fd, shm_fd;
  struct stat stat_buffer;
  char buffer[BUFFER_SIZE];
  int retval;
  off_t left;
  file_fd = open ("./test-mmap.c", O_RDONLY);
  retval = fstat(file_fd, &stat_buffer);
  assert (retval != -1);
  shm_fd = shm_open ("my-test", O_RDWR | O_CREAT, S_IRWXU);
  assert (shm_fd != -1);
  retval = ftruncate (shm_fd, stat_buffer.st_size);
  assert (retval != -1);
  left = stat_buffer.st_size;
  while (left > 0) {
    off_t to_read;
    ssize_t actually_read;
    ssize_t actually_written;
    if (left > BUFFER_SIZE) {
      to_read = BUFFER_SIZE;
    } else {
      to_read = left;
    }
    actually_read = read (file_fd, buffer, to_read);
    assert (actually_read != -1);
    actually_written = write (shm_fd, buffer, actually_read);
    assert (actually_written == actually_read);
    left -= actually_read;
  }
  close (file_fd);

  printf ("done copying file to shared memory\n");

  // Here, we have a shared memory segment which contains the content of our file.

  {
    void *map_one;
    void *map_two;
    char *one;
    char *two;
    map_one = mmap (0, stat_buffer.st_size, PROT_READ | PROT_EXEC | PROT_WRITE, MAP_SHARED, shm_fd, 0);
    assert (map_one != MAP_FAILED);
    map_two = mmap (0, stat_buffer.st_size, PROT_READ | PROT_EXEC | PROT_WRITE, MAP_SHARED, shm_fd, 0);
    assert (map_two != MAP_FAILED);

    one = map_one;
    two = map_two;
    printf ("one=%c\n", one[10]);
    printf ("two=%c\n", two[10]);    
    one[10] = 'Y';
    msync (map_one, stat_buffer.st_size, MS_SYNC);
    printf ("one=%c\n", one[10]);
    printf ("two=%c\n", two[10]);    


    retval = munmap (map_one, stat_buffer.st_size);
    assert (retval != -1);
    retval = munmap (map_two, stat_buffer.st_size);
    assert (retval != -1);
  }


  return 0;
}