Terminal I/O routines - Kernel or User

[David W. Vezie]

I would like to hear what people think about this question:  I am
writing a shell that does some esoteric stuff with the terminal.  It
could either do it in cooked mode (making good use of the t_brkc (4.2
BSD in this case)) or in cbreak mode (where it does all the erase word
kill line kill in user mode in the process itself).  My question is
this:  which is faster?  And which is "cleaner?" Is it better to put it
in the kernel and let the kernel worry about erase/kill stuff along
with my own stuff (possibly adding a second t_brkc (for those of you
who don't know (I'm not sure if brkc is in SysV), brkc is a character
that operates in cooked mode and acts as a newline (terminating the
line, gets echoed, and gets passed back to the user))), or is it better
to make the user program worry about the all the normal input editing
stuff (basically imitate the kernel in cooked mode) as well as the
additional stuff?

There are advantages of both, I think.  To put it in user mode is
cleaner (it doesn't entail any kernel changes, and keeps the kernel
as empty as possible), while to put it in the kernel would probably
be faster (only one context switch per normal line as opposed to
every character).

Comments?

-- 
David W. Vezie		 /!well!dv - Whole Earth 'Lectronics Link, Sausalito, CA
	    {dual|hplabs}
(4 lines, 166 chars)	 \!unicom!dave - College of Marin, Kentfield, CA