enhance makedumpfile to dump process list from vmcore

[HAGIO KAZUHITO(萩尾 一仁)]

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

Thanks,
Kazu