Working with the Unix OS

Figure 43. Pushing a Module onto a Stream
I/O Subsystem
Figure 44. Windowing VT
on Physical Terminal
/* assume file descriptors 0 and 1 already refer to physical tty */
for (;;) /* loop */
{
select (input); /* wait for some line with input */
read input line;
switch (line with input data)
{
case physical tty: /* input on physical tty line */
if (control command) /* e.g. create new window */
{
open a free pseudo-tty;
fork a new process:
if (parent)
{
push a msg discipline on mpx side;
continue; /* back to for loop */
}
/* child here */
close unnecessary file descriptors;
open other member of pseudo-tty pair, get stdin, stdout, stderr;
push tty line discipline;
exec shell; /* looks like virtual tty */
}
/* "regular" data from tty coming up for virtual tty */
demultiplex data read from physical tty,
strip off headers and write to appropriate pty;
continue; /* back to for loop */
case logical tty: /* a virtual tty is writing a window */
encode header indicating what window data is for;
write header and data to physical tty;
continue; /* back to for loop */
}
}
Figure 45. Pseudo-code for
Multiplexing Windows
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