/*
 * Example of using memory-mapped I/O.
 *
 * Change all upper case in a text file to lower case, in place.
 * Name of file supplied as command-line argument.
 */
#include <sys/mman.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <ctype.h>

int main(int argc, char * argv[]) {

    if (argc != 2) {
        fprintf(stderr, "usage:  %s filename\n", argv[0]);
        return EXIT_FAILURE;
    }

    int fd = open(argv[1], O_RDWR);
    if (fd == -1) {
        perror("open");
        return EXIT_FAILURE;
    }

    struct stat file_stats;
    if (fstat(fd, &file_stats) == -1) {
        perror("fstat");
        return EXIT_FAILURE;
    }

    off_t length = file_stats.st_size;

    char * mapped = mmap(NULL, length, PROT_READ | PROT_WRITE, 
            MAP_SHARED, fd, 0);
    if (mapped == MAP_FAILED) {
        perror("mmap");
        return EXIT_FAILURE;
    }

    long count = 0;
    for (off_t i = 0; i < length; ++i) {
        char ch = mapped[i];
        if (isupper(ch)) {
            mapped[i] = tolower(ch);
            count += 1;
        }
    }
    if (msync(mapped, length, MS_SYNC) == -1) {
        perror("msync");
        return EXIT_FAILURE;
    }
    if (munmap(mapped, length) == -1) {
        perror("munmap");
        return EXIT_FAILURE;
    }
    close(fd);

    printf("%ld characters changed\n", count);

    return EXIT_SUCCESS;
}