linux-kernel - Re: printf internals

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Message-ID: <1a9da18c0712191604u5a230382t5ad99a6f464416e5@mail.gmail.com>
Date:	Wed, 19 Dec 2007 16:04:30 -0800
From:	"Masoud Sharbiani \"مسعود شربیانی\"" 
	<masouds@...oud.ir>
To:	"Siva Prasad" <sprasad@...io.net>
Cc:	"Scott Russell" <catfather@...poo.net>,
	"Clemens Koller" <clemens.koller@...gramm.de>,
	"David Newall" <david@...idnewall.com>,
	linux-kernel@...r.kernel.org
Subject: Re: printf internals

On 12/19/07, Siva Prasad <sprasad@...io.net> wrote:
>
> Yes!... this is a embedded system, and will not have monitor. So, serial
> is the default console.
>
> I pass cmdline as "root=/dev/ram rw console=ttyS0,115200"

Adding a CONSOLE=/dev/ttyS0 works for me on both Debian and Redhat;
You also want a inittab entry for console on serial device. (use
google and find it yourself).
cheers,
Masoud

> Thanks
> Siva
>
>
> -----Original Message-----
> From: Scott Russell [mailto:catfather@...poo.net]
> Sent: Wednesday, December 19, 2007 3:31 PM
> To: Siva Prasad
> Cc: Clemens Koller; David Newall; linux-kernel@...r.kernel.org
> Subject: RE: printf internals
>
>
> On Wed, 2007-12-19 at 14:33 -0800, Siva Prasad wrote:
> > 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.
>
> This sounds like you're printing out the serial console instead.
>
> --
> Scott <catfather@...poo.net>
> AIM: BlueCame1
>
> --
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