S01_PLIKI_05

/*
Powtórz zadanie trzecie używając fcntl() i blokując wybrane fragmenty pliku.
*/

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

#define BUFFER_SIZE 128

int main(int argc, char *argv[])
{
    char *filename = (char *)malloc(sizeof(strlen(argv[0]) + strlen(".c") + 1));
    filename = strcat(argv[0], ".c");

    int first_fd, second_fd;
    char buffer[BUFFER_SIZE];
    int result;
    struct flock file_lock;

    if((first_fd = open(filename, O_RDONLY | 0600)) == -1) {
        perror("open");
        return EXIT_FAILURE;
    }

    if((second_fd = fcntl(first_fd, F_DUPFD)) == -1) {
        perror("fcntl_1");
        return EXIT_FAILURE;
    }

    file_lock.l_type = F_RDLCK;
    file_lock.l_whence = SEEK_SET;
    file_lock.l_start = 16;
    file_lock.l_len = 64;

    if(fcntl(second_fd, F_SETLKW, &file_lock) == -1) {
        perror("fcntl_2");
        return EXIT_FAILURE;
    }

    printf("Odczytywanie pliku za pomoca skopiowanego deskryptora: \n");

    for(;;) {
        memset(buffer, '\0', BUFFER_SIZE);
        result = read(second_fd, buffer, BUFFER_SIZE-1);
        if(result == -1) {
            perror("read");
            return EXIT_FAILURE;
        }
        else if(result == 0)
            break;
        else
            printf("%s", buffer);
    }

    printf("\n");

    file_lock.l_type = F_UNLCK;

    if(fcntl(second_fd, F_SETLK, &file_lock) == -1) {
        perror("fnctl_3");
        return EXIT_FAILURE;
    }

    if(close(first_fd) || close(second_fd)) {
        perror("close");
        return EXIT_FAILURE;
    }

    return EXIT_SUCCESS;
}