/* 
 * mmap() example 4.
 *
 * mmap over our own data segment, making global variables
 * persistent.
 *
 * G. Back CS 3214 Fall 2009
 */
#include <sys/types.h>
#include <sys/mman.h>
#include <sys/wait.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <stdio.h>
#include <fcntl.h>
#include <assert.h>
#include <stdbool.h>

#define PGSIZE 4096

char persistent_data[PGSIZE] __attribute__((aligned(PGSIZE)));

/* Make variable 'variableaddr' of size 'size' persistent
 * in file 'filename'
 */
static void
persist(const char *filename, void *variableaddr, 
        size_t size)
{
    assert (size % getpagesize() == 0);
    int fd = open(filename, O_RDWR | O_CREAT, 0666);
    assert (fd != -1);
    assert (ftruncate(fd, size) == 0);

    void *addr = mmap(variableaddr, size,
                      PROT_READ | PROT_WRITE, 
                      MAP_FIXED | MAP_SHARED, fd, 0);
    assert (addr == variableaddr);
    assert (close(fd) == 0);
}

int
main(int ac, char *av[])
{
    int i, do_read = ac < 2 || strcmp(av[1], "-read") == 0;

    persist(".persistent_data", persistent_data, sizeof (persistent_data));

    if (do_read) {
        for (i = 0; persistent_data[i] != 0 && i < PGSIZE; i++)
            fputc(persistent_data[i], stdout);
    } else {
        int c;
        for (i = 0; i < PGSIZE && (c = fgetc(stdin)) != -1; i++)
            persistent_data[i] = c;

        memset(persistent_data + i, 0, PGSIZE - i); // zero rest
    }
    return 0;
}