linux-kernel - Re: Print long messages to console from kernel module

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Message-ID: <Pine.LNX.4.61.0802251722400.2031@chaos.analogic.com>
Date:	Mon, 25 Feb 2008 17:27:37 -0500
From:	"linux-os (Dick Johnson)" <linux-os@...logic.com>
To:	"Arvid Brodin" <arvid.brodin@...a.com>
Cc:	<linux-kernel@...r.kernel.org>
Subject: Re: Print long messages to console from kernel module

On Mon, 25 Feb 2008, Arvid Brodin wrote:

> I need to write messages > 1023 characters long to the console from a module*. printk() is limited to 1023 characters, and splitting the message over several printk()'s results in a line break and "Month hh:mm:ss host kernel:" being inserted in my text.
>
> I tried including <linux/console.h> and using the console_drivers declared there, but get
> "WARNING: "console_drivers" [<path>/log.ko] undefined!" when compiling and
> "insmod: error inserting 'log.ko': -1 Unknown symbol in module" when insmodding.
>
> I guess this is because non EXPORT_SYMBOL'd symbols are only accessible to statically linked code, and not to modules? I see in printk.c that console_drivers is set up there, and I haven't been able to find any other interface to console_drivers.
>
> In short: is there any way to print messages to the console from a kernel module, except printk()? Is opening /dev/tty and writing to it the way to go?
>
>
> * I'm writing an in-memory logger to be included in a module. The log can be several megabytes. The idea is to use SysRq to print the contents of the log to console after a kernel panic or otherwise when writing to disk might not work.
>
> -- 
> Arvid Brodin
> Enea LCC

Write the data to a kernel buffer. Impliment read() or ioctl() and
poll(). Have a user-mode task sleep in poll, waiting for data to
become available. That user-mode task can do anything it wants,
unrestricted, with the data including writing it to files or any
tty it wants to open.

Cheers,
Dick Johnson
Penguin : Linux version 2.6.22.1 on an i686 machine (5588.28 BogoMips).
My book : http://www.AbominableFirebug.com/
_

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