Ping pong a byte over pipes and measure the exchanges (xv6 1.6 exercise)

pingpong.c

#include <unistd.h>
#include <stdio.h>
#include <signal.h>
#include <stdlib.h>

size_t n_read;

void handle_alarm(int signum) {
    printf("n_read = %lu\n", n_read);
    fflush(NULL);
    n_read = 0;
    alarm(1);
}

int main(int argc, char **argv)
{
    int p2c[2];
    int c2p[2];

    n_read = 0;

    if (pipe(p2c) == -1) {
        perror("pipe");
        exit(1);
    }

    if (pipe(c2p) == -1) {
        perror("pipe");
        exit(1);
    }

    pid_t p = fork();

    if (p == -1) {
        perror("fork");
        exit(1);
    }

    if (p == 0) {
        close(p2c[1]);
        close(c2p[0]);
        signal(SIGALRM, handle_alarm);
        alarm(1);
        while (1) {
            unsigned char c;

            if (read(p2c[0], &c, 1) == -1) {
                perror("child read");
                exit(1);
            }

            if (write(c2p[1], &c, 1) == -1) {
                perror("child write");
                exit(1);
            }

            n_read++;
        }
    }

    unsigned char c = 'X';
    signal(SIGALRM, handle_alarm);
    alarm(1);
    while (1) {
        if (write(p2c[1], &c, 1) == -1) {
            perror("parent write");
            exit(1);
        }

        if (read(c2p[0], &c, 1) == -1) {
            perror("parent read");
            exit(1);
        }

        n_read++;
    }
}