From: "Richard D" <richard@embunus.com>
To: "'Siva Prasad'" <sprasad@bivio.net>,
       "'Clemens Koller'" <clemens.koller@anagramm.de>,
       "'David Newall'" <david@davidnewall.com>
Cc: <linux-kernel@vger.kernel.org>
References: <D83235F0F3C86D4D889D8B9A0DA8C6D7011A8217@corpexc01.corp.networkrobots.com> <4761E289.9070007@davidnewall.com> <4762AC35.3010706@anagramm.de> <D83235F0F3C86D4D889D8B9A0DA8C6D7012AF540@corpexc01.corp.networkrobots.com>
In-Reply-To: <D83235F0F3C86D4D889D8B9A0DA8C6D7012AF540@corpexc01.corp.networkrobots.com>
Subject: RE: printf internals
Date: Sat, 22 Dec 2007 09:12:43 +0530
Message-ID: <009201c8444c$ba0d82b0$2e288810$@com>
MIME-Version: 1.0
Content-Type: text/plain;
	charset="iso-8859-1"
Content-Transfer-Encoding: 8BIT
Thread-Index: Acg+bB2ZyI+LjZ4IQKaXKiKorA2z3gEIdW2QAG+sKOA=
Content-Language: en-us
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 3052
Lines: 86

Most likely your device nodes are missing in /dev. 

-----Original Message-----
From: linux-kernel-owner@vger.kernel.org
[mailto:linux-kernel-owner@vger.kernel.org] On Behalf Of Siva Prasad
Sent: Thursday, December 20, 2007 4:03 AM
To: Clemens Koller; David Newall
Cc: linux-kernel@vger.kernel.org
Subject: RE: printf internals

Thank you very much for your response Clemens.

I tried strace on a regular system. It does not show which tty, etc., as it
uses the stdout (fd = 1) and write(1, ...) to it.

This is not a student project. I am trying to build my own kernel and
ramdisk. Kernel boots fine to a point where it starts accessing ramdisk and
executes init scripts. From there on nothing gets printed. I did some
debugging and found that prints of user land programs are not coming to the
serial console, while kernel prints are working fine. I found all the
programs getting executed, by placing a printk in execve routine and
printing the arguments.

So, I wanted to trace down the path from user program to the kernel and see
why it is not printing messages from user program. I placed a printk in
drivers/char/tty_io.c:tty_write() and it is not getting called from my file
system. I tried the same thing on my good system (say regular PC) and it
works as expected.

Any clues that can help debug this issue is highly appreciated.
How can I get access to the same printf string inside kernel.

Thanks
Siva


-----Original Message-----
From: Clemens Koller [mailto:clemens.koller@anagramm.de] 
Sent: Friday, December 14, 2007 8:16 AM
To: David Newall
Cc: Siva Prasad; linux-kernel@vger.kernel.org
Subject: Re: printf internals

David Newall schrieb:
 > Siva Prasad wrote:
 >> I am looking at how exactly does the printf in user programs succeeds in
 >> displaying characters to the serial console.
 >
 > Is it a student assignment?  This is so not the right mailing list.

Come on, are we playing hide and seek here?

You can use strace to follow a typical hello world example and
see what device it opens to feed the hello out.
I.e. it can be to the current /dev/ttyX and not to /dev/console
or if you are logged in via SSH to a machine, the device
is again different... or if you use screen, ...

Work your way from there and then use a Linux Source code
Cross Reference (lxr, ask Google for one) and follow the code.

Regards,
-- 
Clemens Koller
__________________________________
R&D Imaging Devices
Anagramm GmbH
Rupert-Mayer-Stra?e 45/1
Linhof Werksgel?nde
D-81379 M?nchen
Tel.089-741518-50
Fax 089-741518-19
http://www.anagramm-technology.com

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/