Messages in this thread |  | | Date | Thu, 21 Mar 2019 11:20:13 +0100 | From | Petr Mladek <> | Subject | Re: [PATCH] printk: Add caller information to printk() output. |
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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
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