Help with line disciplines

[Kenneth Almquist]

Unfortunately, line disciplines are not well documented.  As I recall,
l_open is called every time an open system call is done on the device,
and l_close is called when a close system call is done and nothing else
has the device open.  When a program is run from the shell, the tty is
not opened (instead it inherits its file descriptors from the shell) so
the l_open routine is not called.

I'm not sure it is "correct" to access the u structure from within a
device driver, but it should word as the routine accessing the structure
was invoked from a system call rather than an interrupt.

To find all the processes in a process group, you have to search the
process table.  This is an array of proc structures (defined in sys/proc.h)
named proc.  There is also a routine (gsignal, I think) that will send
a signal to all processes in a process group.
				Kenneth Almquist