Programming

I need help with understanding this in C-programming style(the systemcalls only):
Three processes communicates via two pipes. (when the processes creates all stdin is the keyboard and all stdout is the screen)

This is how the communication goes:
Process 2 stdin (keyboard) and stdout goes via pipe2, this then becomes process 3:s stdin, and process 3:s stdout goes through pipe1, and then becomes Process 1:s stdin, Process 1:s stdout goes to the screen.

What is the system calls from each process(1, 2, 3)?
for example:
close(0);
dup(pipe2[0]);
etc,

(Don´t need to make a close where the need comes from the processes relationships)

Please help out! I just want the correct systemcalls, with the correct pipe and read or write end, so I get this finally :-)

If you have to connect existing processes with pipes, you'll need to use named pipes, which can be created with the mkfifo() call and opened with the open() syscall, and duplicated over the required FD's with the dup2() syscall.

What's generally done so as to use anonymous pipes, is the parent process creates the necessary pipes with the pipe() syscall, does its own redirections with dup2(), forks, then the child does its own redirections. Any unnecessary duplicates of the pipe descriptors should be closed as soon as possible so your processes don't end up waiting on them.

No that was not the answer i was looking for, I don´t think you understood my questions correct, I have example, and how the communication goes. But thank you anyway.

You're missing my point. You can't connect processes that already exist with anonymous pipes. Therefore the instructions you want, connecting any 3 processes with pipes, simply don't exist.

All of the pipes must be created in the parent first. That way, when it creates children, they will share these pipes, allowing them(and of course the parent) to redirect their I/O through them how they please. To give more detailed instructions I'll need to know which of your processes created which others.