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

int main(int argc, char *argv[])
{
    if (argc < 2) {
        printf("no file\n");
        return 1;
    }

    int fd = open(argv[1], O_RDONLY);

    if (fd < 0) {
        perror("file open error");
        return 1;
    }

    struct stat s;
    if (fstat(fd, &s) < 0) {
        perror("cannot stat file");
        return 1;
    }

    long a = 0;

    void *addr = mmap(NULL, s.st_size, PROT_READ, MAP_PRIVATE, fd, 0);

    if (addr == MAP_FAILED) {
        perror("cannot map file");
        return 1;
    }

    for (off_t i = 0; i < s.st_size; ++i) {
        if (((char *)addr)[i] == 'a')
            ++a;
    }

    printf("Result: %ld\n", a);

    munmap(addr, s.st_size);
    close(fd);

    return 0;
}