Pipe creation through functions - c

Question

I was wondering if someone can help me modify my current code....
Currently it creates my process using fork() and takes a pointer to a function which executes that childs code block.
I wanted to play around with pipes and attempt to now have Process Y send its pid to Process X and then i want to send it back to the Main...
Heres what i have currently
#include <unistd.h>
#include <stdio.h>
#include <signal.h>
#include <stdlib.h> // exit
#include <fcntl.h>
#include <sys/wait.h>
void processX();
void processY();
pid_t addChild(void (*childPtr) (), int fileDes[2]) {
pid_t cpid;
if((cpid=fork()) == 0) {
pipe(fileDes);
childPtr(fileDes);
wait(NULL);
exit(0);
} else if (cpid < 0) {
printf("failed to fork");
exit(1);
} else {
}
return cpid;
}
void processY(int fileDes[2]) {
printf("Child Y[%d] Created of Parent X[%d]\n", getpid(), getppid());
printf("We are now going to write Y PID to process X\n");
pid_t a = getpid();
char buf[1024]; // child reads from pipe() to buffer
close(fileDes[0]); // close reading end of the pipe
write(fileDes[1], &a, sizeof(buf) / sizeof(int));
}
void processX(int fileDes[2]) {
printf("Child X[%d] Created of parent Main[%d]\n", getpid(), getppid());
int status;
pid_t Y = addChild(processY, fileDes);
wait(&status);
pid_t new_val = 5;
close(fileDes[1]); // closing the writing end of the pipe.
read(fileDes[0], &new_val, sizeof(new_val));
printf("Message read with number %d: \n", new_val);
}
int main() {
int status;
int fd[2];
printf("Main process[%d]\n", getpid());
pid_t root = addChild(processX, fd);
wait(&status);
printf("We are going to read from X to Main and then return the Value we got from Y\n");
return 0;
}
I dont know to create a pipe from Y - X and then X - Main....
Y---->send pid ----> X received Y pid ----- send new info to main --->Main print received data...

Answer 1

My answer i came up with
#include <unistd.h>
#include <stdio.h>
#include <signal.h>
#include <stdlib.h> // exit
#include <fcntl.h>
#include <sys/wait.h>
void processX();
void processY();
pid_t addChild(void (*childPtr) (), int fileDes[2], int backToMainFd[2]) {
pid_t cpid;
if(childPtr != *processX //prevents the the pipe from main to x from recreating
pipe(fileDes);
if((cpid=fork()) == 0) {
if(childPtr == *processX) {
childPtr(fileDes, backToMainFd);
} else {
childPtr(fileDes);
}
wait(NULL);
exit(0);
} else if (cpid < 0) {
printf("failed to fork");
exit(1);
} else {
}
return cpid;
}
void processY(int fileDes[2]) {
printf("[PROCESS Y]: Child Y[%d] Created of Parent X[%d]\n", getpid(), getppid());
pid_t a = getpid();
char buf[1024]; // child reads from pipe() to buffer
close(fileDes[0]); // close reading end of the pipe
write(fileDes[1], &a, sizeof(buf) / sizeof(int));
}
void processX(int fileDes[2], int BackToMainFd[2]) {
printf("[PROCESS X]: Child X[%d] Created of parent Main[%d]\n", getpid(), getppid());
int status;
pid_t Y = addChild(processY, fileDes, NULL);
wait(&status);
pid_t new_val = 5;
close(fileDes[1]); // closing the writing end of the pipe.
read(fileDes[0], &new_val, sizeof(new_val));
printf("[PROCESS X]: We got Ys' PID as:%d from [PROCESS Y]\n", new_val);
close(BackToMainFd[0]); // close reading end of the pipe
char buf[1024]; // child reads from pipe() to buffer
write(BackToMainFd[1], &new_val, sizeof(buf) / sizeof(pid_t));
}
int main() {
int status;
int fd[2];
int backToMainFD[2];
printf("Main process[%d]\n", getpid());
pipe(backToMainFD);
pid_t root = addChild(processX, fd, backToMainFD);
wait(&status);
pid_t new_val = 5;
close(backToMainFD[1]); // closing the writing end of the pipe.
read(backToMainFD[0], &new_val, sizeof(new_val));
printf("[MAIN]: We got Ys' PID as:%d from [PROCESS X]\n", new_val);
printf("Send sig kills too Y and root\n");
kill(new_val, SIGKILL);
kill(root, SIGKILL);
printf("Terminate program.\n");
return 0;
}