/*
 * writer.c
 */

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

int main(int argc, char *argv[])
{
    char *file_data;
    struct stat sb;
    int fd;
    char buf[1];

    /* open the file */
    if((fd = open("test-file", O_RDWR)) < 0) {
        perror("open");
        exit(1);
    }

    /* get file metadata, most especially its size */
    if(fstat(fd, &sb) < 0) {
        perror("fstat");
        exit(2);
    }

    /* set up the mapping */
    file_data = mmap(NULL, sb.st_size, PROT_READ | PROT_WRITE, MAP_PRIVATE, fd, 0);

    /* pause */
    write(1, "hit enter to write\n", 19);
    read(0, buf, 1);

    /* modify the file by messing with the mapped memory */
    memcpy(file_data + 8, "MINE", 4);

    printf("in memory now: \"%s\"\n", file_data);

    /* pause */
    write(1, "hit enter to munmap file\n", 25);
    read(0, buf, 1);

    /* clean up after ourselves */
    munmap(file_data, sb.st_size);
    close(fd);
}