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SubjectRe: design-question serial-driver + predefined ldisc - Nuber
   Date: 	Tue, 8 Aug 2000 14:29:20 +0200
From: Michael Westermann <mw@microdata-pos.de>

I hav a projekt for POS-Systeme with a few driver's that
all use a protokoll over the serial device.
I think it is a goo idea when i use the ldisc mechanism
from the tty driver.

My problem is that the ldiscs array in tty_io.c is static
predefined. I have 3 to 10 protokoll's over this mechnism.

I think it is a good idea, to create a dynamic part on the ldiscs
structure.

So your idea is to have a range of line discplines from N_LDDYN and
NR_LDISCS would be dynamically allocated? It seems like a good concept,
but (a) not for Linux 2.4, (b) don't overload the return value of
tty_register_ldisc (it's ugly, ugly, ugly), and (c) the dynamic line
discplines (and arguably all of the other line discplines, in the long
run) should probably use an ASCII string instead of a number to address
them.

Linus hates magic numbers, and while in some cases they are necessary,
line discplines are a perfect example of where a new ioctl where you
pass in a 32 byte character array containing a null-terminated string
naming the line discpline you want is almost certainly the Right Thing.
Unfortunately, it's not for 2.4, but that's probably the right approach
to use, and hopefully we can merge a patch like that in once the 2.5
development opens.

- Ted


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