/*
 * Copyright 2002-2019 Intel Corporation.
 * 
 * This software is provided to you as Sample Source Code as defined in the accompanying
 * End User License Agreement for the Intel(R) Software Development Products ("Agreement")
 * section 1.L.
 * 
 * This software and the related documents are provided as is, with no express or implied
 * warranties, other than those that are expressly stated in the License.
 */

#include <sched.h>
#include <unistd.h>
#include <fcntl.h>
#include <cstdlib>
#include <cstdio>
#include <cstring>
#include <cerrno>


/* Stack size for cloned child */
#define STACK_SIZE (1024 * 1024)

#define errExit(msg)    do { perror(msg); exit(EXIT_FAILURE); \
                        } while (0)

/* Pipe for connection between main process and child */
int myPipe[2];

/* Start function for cloned child */
static int childFunc(void *arg)
{
    /* Close unused read side */
    close(myPipe[0]);

    /* Write to the pipe */
    write(myPipe[1], "child wrote!!", strlen("child wrote!!"));

    /* exit() closes the write side */
    exit(EXIT_SUCCESS);
}

/* main function */
int main(int argc, char *argv[])
{
    char * stack = NULL;
    char * stackTop = NULL;
    char buf = '\0';
    int oldStatus = -1;
    pid_t pid = -1;

    /* Allocate stack for child */
    stack = (char*)malloc(STACK_SIZE);
    if (NULL == stack)
    {
        errExit("malloc");
    }
    stackTop = stack + STACK_SIZE;

    /* Inialize pipe */
    if (-1 == pipe(myPipe))
    {
        errExit("pipe");
    }

    /* Set read side to fail if the write side still empty */
    oldStatus = fcntl(myPipe[0], F_GETFL);
    if (-1 == oldStatus)
    {
        errExit("fcntl");
    }
    fcntl(myPipe[0], F_SETFL, oldStatus|O_NONBLOCK);

    /* Create child */
    pid = clone(childFunc, stackTop, CLONE_VFORK, NULL);
    if (-1 == pid)
    {
        errExit("clone");
    }

    /* Close unused write side */
    close(myPipe[1]);

    /* Try to read from pipe, the child should already wrote to the pipe */
    if (-1 == read(myPipe[0], &buf, 1))
    {
        errExit("nonBlocking read failed!");
    }

    /* Close read side */
    close(myPipe[0]);

    free(stack);

    exit(EXIT_SUCCESS);
}