lkml.org 
[lkml]   [2019]   [Mar]   [21]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH] printk: Add caller information to printk() output.
On Thu 2019-03-21 13:59:53, Michael Ellerman wrote:
> Hi Tetsuo,
>
> Thanks for implementing this, it's really helpful.
>
> Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp> writes:
> ...
> > From 91f85d2bd494df2f73c605d8b4747e8cc0a61ae2 Mon Sep 17 00:00:00 2001
> > From: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
> > Date: Tue, 18 Dec 2018 05:53:04 +0900
> > Subject: [PATCH] printk: Add caller information to printk() output.
> >
> > Sometimes we want to print a series of printk() messages to consoles
> > without being disturbed by concurrent printk() from interrupts and/or
> > other threads. But we can't enforce printk() callers to use their local
> > buffers because we need to ask them to make too much changes. Also, even
> > buffering up to one line inside printk() might cause failing to emit
> > an important clue under critical situation.
> >
> > Therefore, instead of trying to help buffering, let's try to help
> > reconstructing messages by saving caller information as of calling
> > log_store() and adding it as "[T$thread_id]" or "[C$processor_id]"
> > upon printing to consoles.
> >
> > Some examples for console output:
> >
> > [ 1.222773][ T1] x86: Booting SMP configuration:
> > [ 2.779635][ T1] pci 0000:00:01.0: PCI bridge to [bus 01]
> > [ 5.069193][ T268] Fusion MPT base driver 3.04.20
> > [ 9.316504][ C2] random: fast init done
> > [ 13.413336][ T3355] Initialized host personality
> >
> > Some examples for /dev/kmsg output:
> >
> > 6,496,1222773,-,caller=T1;x86: Booting SMP configuration:
> > 6,968,2779635,-,caller=T1;pci 0000:00:01.0: PCI bridge to [bus 01]
> > SUBSYSTEM=pci
> > DEVICE=+pci:0000:00:01.0
> > 6,1353,5069193,-,caller=T268;Fusion MPT base driver 3.04.20
> > 5,1526,9316504,-,caller=C2;random: fast init done
> > 6,1575,13413336,-,caller=T3355;Initialized host personality
> >
> > Note that this patch changes max length of messages which can be printed
> > by printk() or written to /dev/kmsg interface from 992 bytes to 976 bytes,
> > based on an assumption that userspace won't try to write messages hitting
> > that border line to /dev/kmsg interface.
>
> Do you have any plans to update dmesg or other userspace tools to show
> the caller information?

dmesg already works via the syslog interface, try dmesg -S.

The current implementation does not pass the information into
the /dev/kmsg interface. It has the following format:

"<level>,<sequnum>,<timestamp>,<contflag>[,additional_values, ... ];<message text>\n"

It would be possible to add it as an additional value. To be hones
I am not sure how they are handled by userspace tools.

Best Regards,
Petr

\
 
 \ /
  Last update: 2019-03-21 11:21    [W:0.162 / U:2.408 seconds]
©2003-2018 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site