Re: [Crash-utility] [RFC] Crash extension for SystemTap

[Dave Anderson <anderson at redhat dot com>]

Satoru MORIYA wrote:
> Hi,
>
> Here is an extension(shared object) of the crash to retrieve the trace
> data of systemtap scripts.

Hi Satoru,

I think you also meant to attach the stplog.c (and its own Makefile?)
to your post?

Is the format of the trace data used by systemtap always the same?
I.e., is it always a kernel buffer filled with ASCII data?

You mention that the command makes a file in a subdirectory of the
running crash session.  Wouldn't it be more flexible to dump the
output to the terminal?  And then if you want to save it to a file,
just do something like this:

 crash> stplog -m mod_name > outputfile

Anyway, I think it's time that I create a repository for extensions
on my people site...

Thanks,
  Dave


> I'd like to analyze what caused the kernel panic by using the systemtap.
> However, currently the systemtap's trace data can't be retrieved from a
> dumped image easily. So, I developed a crash's extension which retrieves
> the data recorded by systemtap from the dumped image.
> Here is a brief document of this extension. This extension supports the new
> utt-based buffer as well as the bulk-mode buffer of old systemtap module.
>
> I have tested this extention on the following system.
>   * FC6, i386, kernel-2.6.21, systemtap-0.5.14, crash-4.0-1.1
>   * FC6, i386, kernel-2.6.20, systemtap-0.5.13/14, crash-4.0-1.1
>   * RHEL5, i386, kernel-2.6.18-8.el5, systemtap-0.5.12, crash-4.0-3.14
>
>
> Preparation
> ==============
> (A) Build the shared-object(stplog.so).
>
> 1. Put Makefile and stplog.c into a directory ($DIR)
>     $ cd $DIR
>
> 2. Make the symbolic link to the crash source code directory
>     $ ln -s $WHERE_CRASH_PLACED crash
>
> 3. Build
>     $ make
>
> (B) Make the crash dump which includes SystemTap trace data.
>     (*)If you analyze the live system memory, ignore this section.
>
> 1. Install kdump
>      If you use FC6, see following URL.
>      http://fedoraproject.org/wiki/FC6KdumpKexecHowTo?highlight=%28kdump%29
>
> 2. Use SystemTap
>     $ stap foo.stp
>
> 3. Panic
>     $ echo c > /proc/sysrq-trigger
>
> How to use
> ==============
> 1. start crash
>     $ crash vmlinux vmcore
>     (*) If you analyze the live system memory, you don't need "vmcore".
>          $ crash vmlinux
>
> 2. load the shared-object
>     crash> extend $(WHERE_OBJ_PLACED)/stplog.so
>
> 3. retrieve the data
>     crash> stplog -m <mod_name>
>     (*) <mod_name> is the name of trace module from which you retrieve data.
>
> 4. You can get output files under the directory whose name is <mod_name>.
>
> Output
> ==============
> stplog command makes a file per channel buffer of relayfs(equivalent to per cpu).
> And it also removes padding bytes.
>
>
> I believe this command is very useful for system administrators
> if they monitor their systems with SystemTap.
>
> Best Regards,
>
> ---
> Satoru MORIYA
> Linux Technology Center
> Hitachi, Ltd., Systems Development Laboratory
> E-mail: satoru.moriya.br@hitachi.com
>
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