linux-kernel - Best way to do kernel only ldisc without user-space ldisc attaching?

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Date:	Tue, 13 Apr 2010 10:56:19 +0200
From:	Florian Fainelli <florian@...nwrt.org>
To:	linux-kernel@...r.kernel.org
Cc:	alan@...rguk.ukuu.org.uk, gregkh@...e.de
Subject: Best way to do kernel only ldisc without user-space ldisc attaching?

Hello,

I have a line discpline driver for a custom protocol over an UART. This driver 
implements the following callbacks: open/close, receive_buf/write_wakeup.

So far, I have an ugly hack, which opens the /dev/tty<N> in the kernel, and 
directly uses the f_op and unlocked_ioctl functions to do the ldisc number to 
TTY device binding:

[snip]
struct file *f;

filp_open("/dev/ttyS1", 0, 0);

f->f_op->unlocked_ioctl(f, TCFLSH, 0x2);
memset(&tio, 0, sizeof(tio));
tio.c_cflag = my_flags;
tio.c_iflag = IGNPAR | ICRNL;
f->f_op->unlocked_ioctl(f, TCSETS, (long unsigned int)&tio);
f->f_op->unlocked_ioctl(f, TIOCSETD, (long unsigned int)&ldisc_nr);
set_fs(oldfs);
[snip]

This prevents me from rmmoding the module. However, I would like to avoid an 
user-space program from having to bind the TTY device to the ldisc number if 
possible.

Thank you very much for your answer.
--
Florian
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