linux-kernel - Re: request for assistance: accessing ttys from kernel space

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Message-ID: <20100126133958.49e660a5@lxorguk.ukuu.org.uk>
Date:	Tue, 26 Jan 2010 13:39:58 +0000
From:	Alan Cox <alan@...rguk.ukuu.org.uk>
To:	Samuel Thibault <samuel.thibault@...-lyon.org>
Cc:	William Hubbs <w.d.hubbs@...il.com>, linux-kernel@...r.kernel.org,
	linux-serial@...r.kernel.org, gregkh@...e.de,
	Chris Brannon <cmbrannon79@...il.com>,
	Kirk Reiser <kirk@...sers.ca>
Subject: Re: request for assistance:  accessing ttys from kernel space

> Is there another way to set up a line discipline from the kernel itself
> without the need from userland intervention, even before any / is
> mounted?

There is no fundamental reason you can't do that once the tty object
itself exists. Currently there is no path for doing it in the kernel.

> Maybe the early serial console support layer could be extended a bit so
> speakup can use it first during the boot?  For now it's quite tied to
> just printing the printk logs. drivers/accessibility/braille_console.c
> does manage do make something else, but it happens that the
> serial_core.c's uart_console_write puts additional \rs before \ns, which
> can be a problem.
> 
> Also, for proper speech flow, speakup would need to be able to read
> characters from the device.

Some debugger folk want that too.

I've been trying to get to the point where each tty consists of a
tty_struct which is the instance of an opened tty device, and a tty_port
which is a common struct instance for each physical port. That then has
some operations attached to it.

However at the moment most of the operation paths are not pushed into
tty_port, not every device yet has a tty_port and many of the paths that
need pushing into tty_port reference material that is in struct tty but
probably also needs moving.

So there is an awful lot of work to be done.

I guess the quick 'get it working' hack for the moment would be to add a
'raw' flag to the console output routines and use those (where raw=1
would mean 'don't tamper with the formatting')

Alan
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