PTY SOC:
A simple paradigm for attaching shells to a context.

SUMMARY:
    From the context you want to access use "pty @" command to create a control 
    node (FIFO) for your prefered shell. Recommended path is /run/<context>.pty
    ex) pty @ /run/init.pty /bin/bash

    The command does not exit. It will keep listening on the control node.
    You will have to daemonize the command yourself.

    Then from the restricted context (such as a PID namespace), use soc to connect
    to the pty process. You can use Ctrl-d to exit.
    ex) soc /run/init.pty
    
    It is possible to connect multible shells to pty @ at the same time.

    Programs that want to implment a soc in-process should implement functionality
    mirroring the pty @ command. Shell scripts can use the "pty @" command directly.

USAGE:

soc <file>
    1. opens a pty 
    2. write slave path to <file>
    3. waits for something else to open the slave pty
    4. pipes calling context's tty to the master port of the pty
    5. actively mediates pipe untill slave pty is closed or signal recieved

pty </dev/pts/N> <command>
    1. opens the specified pts
    2. forks off process to run command under the pty
    2. waits for child process to finish

pty @ <path> <command>
    1. creates fifo at <path>, deleting any existing fifo
    2. reads lines from fifo, for each line:
        a. interpret line as path to pty slave
        b. open the pty slave
        c. fork process to run command under the pty
    3. reads untill SIGINT, reaps dead children (SIGCHLD)

CREDITS:
author: Erich Spaker [November 2020]
derived from: https://github.com/abligh/pty