Why child process pipe is showing in parent process with different pipe details

Question

I am learning c program fork and pipe. I create a fork shown below.

parent=> child1=>child2

In parent we are creating a pipe.And the file descriptor are stored in parentpip.

In Child1 also i am creating a pipe. And the file descriptor are stored in child1pip.

Now when i check the process id fd in /proc//fd. Below things are getting displayed.

If i do ls -l /proc/15585/fd .. This is for parent

lrwx------ 1 vipin vipin 64 Jan 14 17:33 0 -> /dev/pts/1
lrwx------ 1 vipin vipin 64 Jan 14 17:33 1 -> /dev/pts/1 
lrwx------ 1 vipin vipin 64 Jan 14 17:33 2 -> /dev/pts/1 
lr-x------ 1 vipin vipin 64 Jan 14 17:33 3 -> 'pipe:[354240]' 
l-wx------ 1 vipin vipin 64 Jan 14 17:33 4 -> 'pipe:[354240]' 
lr-x------ 1 vipin vipin 64 Jan 14 17:33 5 -> 'pipe:[354241]' 
l-wx------ 1 vipin vipin 64 Jan 14 17:33 6 -> 'pipe:[354241]' 

If i do ls -l /proc/15586/fd .. This is for child1

 lrwx------ 1 vipin vipin 64 Jan 14 17:33 0 -> /dev/pts/1
lrwx------ 1 vipin vipin 64 Jan 14 17:33 1 -> /dev/pts/1
 lrwx------ 1 vipin vipin 64 Jan 14 17:33 2 -> /dev/pts/1
lr-x------ 1 vipin vipin 64 Jan 14 17:33 3 -> 'pipe:[354240]'
l-wx------ 1 vipin vipin 64 Jan 14 17:33 4 -> 'pipe:[354240]'
lr-x------ 1 vipin vipin 64 Jan 14 17:33 5 -> 'pipe:[357693]'
l-wx------ 1 vipin vipin 64 Jan 14 17:33 6 -> 'pipe:[357693]'

If i do ls -l /proc/15587/fd .. This is for child2

lrwx------ 1 vipin vipin 64 Jan 14 17:33 0 -> /dev/pts/1
lrwx------ 1 vipin vipin 64 Jan 14 17:33 1 -> /dev/pts/1
lrwx------ 1 vipin vipin 64 Jan 14 17:33 2 -> /dev/pts/1
lr-x------ 1 vipin vipin 64 Jan 14 17:33 3 -> 'pipe:[354240]'
l-wx------ 1 vipin vipin 64 Jan 14 17:33 4 -> 'pipe:[354240]'
lr-x------ 1 vipin vipin 64 Jan 14 17:33 5 -> 'pipe:[357693]'
l-wx------ 1 vipin vipin 64 Jan 14 17:33 6 -> 'pipe:[357693]'

Here filedescriptor 3 and 4 is belong to parentpip. So same pipe among all the process pipe:[354240] and pipe:[354240]

When we see filedescriptor 5 and 6 child2 and child1 hold the same child1pip. pipe:[357693] and pipe:[357693]

But i can see 5 and 6 in parent also Why also in parent. And the pip is pipe:[354241] and pipe:[354241]

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


int main(int argc,char * argv[])
{

    int parentpip[2];

    pipe(parentpip);

    int child1pid =fork();

    int child1pip[2];
    pipe(child1pip);

    if(child1pid==0)
    {
        printf("This child1");
        int child2pid2=fork();
        if(child2pid2==0)
        {
          printf("This child2");
        }
        sleep(20*60);
    }
    else
    {
        printf("This parent");
        sleep(20*60) ;
    }

    return 0;
}

Answer 1

You have these things happening.

1. parent creates pipe 354240 stored in parentpip
2. child1 is forked from parent, inheriting pipe 354240
3. parent creates pipe 354241 stored in child1pip
4. child1 creates pipe 357693 stored in child1pip
5. child2 is forked from child1, inheriting pipe 354240 and 357693

Note in point 3, the parent also runs the line of code: pipe(child1pip); creating a new pipe - and so does the child1 process - both these processes creates their own pipes since this happens after fork().

You probably only need child1 to run pipe(child1pip); so change this code:

int child1pip[2];
pipe(child1pip);

if(child1pid==0)
{

To this code:

if(child1pid==0)
{
     int child1pip[2];
     pipe(child1pip