enhance makedumpfile to dump process list from vmcore

[Dave Young]

Hi Kazu,

On Wed, 19 Jun 2024 at 13:45, HAGIO KAZUHITO(萩尾　一仁) <k-hagio-ab at nec.com> wrote:
>
> On 2024/06/06 3:10, Prasad Koya wrote:
> > Hi
> >
> > We use makedumpfile to read the dmesg buffer from the vmcore. We are
> > working on adding a feature to makedumpfile to extract the "process
> > list" from /proc/vmcore. Our main use case is to save the processes
> > that were running at the time of kernel crash to a file on the
> > permanent storage from the kdump kernel. We intend to read a handful
> > of useful data for each running task: pid, parent pid, real parent
> > pid, priority, nice value, RSS, VM size, command, utime, stime, OOM
> > score.
> >
> > Process list from vmcore can probably be read using crash utility, but
> > in our embedded system using makedumpfile to do that job makes sense
> > for us.
> >
> > If such an option is useful for the general users of makedumpfile,
> > we'd like to get more inputs and contribute to this feature.
>
> Hi Prasad,
>
> thank you for sharing the idea.  But sorry, currently we are not
> interested in implementing such a big function in makedumpfile.
>
> The dmesg buffer is the most important information to be able to
> determine the cause of a crash only with it, so the --dump-dmesg option
> was implemented in makedumpfile first once upon a time.  But now we have
> handier vmcore-dmesg command in kexec-tools, so we don't intend to add
> other functions to makedumpfile than making a dumpfile.
>
> I'm not sure whether these are doable, but I would suggest a few ideas
> instead:
> - make e.g. vmcore-process-list command like vmcore-dmesg.

Not sure if this is worth either.    I guess it can be done with some
crash tool scripts or a crash plugin?

> - use panic notifier to dump process list to the dmesg buffer before
> kdump, and use vmcore-dmesg to get it.

It is not recommended to add these before kdump if people still want a
reliable kdump.

>
> Thanks,
> Kazu
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Thanks
Dave
> kexec at lists.infradead.org
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>