linux-kernel - Virutal tty device settings problem.

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Date:	Mon, 31 Oct 2011 16:21:32 +0100
From:	"dpc@...re.info" <dpc@...re.info>
To:	linux-kernel@...r.kernel.org
Subject: Virutal tty device settings problem.

Hi,

I'm writing a virtual console driver for paravirtualized setup.

Use case: being able to access paravirtualized guest consoles from "domain 0".

It's similar to HVCS, as I've been analyzing how it works.

Basically in my driver there's a frontend and backend. Backend is used
by domain 0 exposing tty devices: each for every other guest. One can
attach cu/minicom to such device and access guest console.

The frontend is working on the other guest side and communicate via
shared memory/virtual IRQs with backend. It exposes on tty device for
system console / getty.

Little illustration:

|               GUEST 0               |                  |
 GUEST 1                 |
tty device <--> kernel backend driver <--> magic here <--> kernel
frontend driver <--> tty device
(minicom/cu)
                  (getty)

I have the communication working and my driver transmits bytes between
domain 0 and other systems. So the "magic here" can be considered a
bytestream. But I'm lost with all the modes, cr/nl etc. conversions.

I don't understand which part of the kernel is responsible for NL / CR
conversions, what modes should I use on each side of the driver and
stuff like this. At the moment, from what I understand it seems that
some of termios flags are handled above tty driver layer, and other
should be handled inside/below it. Can anyone point me to documents
explaining this things or explain how should I handle this so that the
scenario from the illustration is working seamlessly?

Any help will be much appreciated.
-- 
Dawid Ciężarkiewicz
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