crashinfo doesn't support compressed crashdumps - which way forward?

[Mark Johnston]

On Thu, Jul 12, 2018 at 09:09:02AM -0700, John Baldwin wrote:
> On 7/12/18 7:31 AM, Mark Johnston wrote:
> > On Thu, Jul 12, 2018 at 02:14:09PM +0200, Alexander Leidinger wrote:
> >> Hi,
> >>
> >> the crashinfo script doesn't know how to handle compressed coredumps.  
> >> What would be acceptable behavior (ordered by my preferrence)?
> >>   1) decompress in /var/crash and then proceed normally (already  
> >> implemented locally)
> >>   2) decompress to CRASHTMPDIR:/var/tmp/xxx and delete when finished
> >>   3) keep it like it is
> >>   4) teach tools to understand compressed dumps (gzip / zstd)
> >>
> >> Implicitly there is the question what what is the purpose of  
> >> compressing crashdumps, to have more RAM than space in dumpdev (which  
> >> is valid in my case), or to save space in /var/crash (which I don't  
> >> care much about).
> > 
> > I think jhb has a patch which implements 2).  I do not have strong
> > feelings on which is the right way forward, but I mildly prefer 2) to
> > 1).  It looks like crashinfo can be disabled in rc.conf, so users who
> > are space-constrained in /var/crash can take the additional step of
> > setting crashinfo_enable=NO.  FWIW, when I committed the compression
> > support, my use-case involved both a small dump device and a small
> > /var filesystem.
> 
> Yes, here's the patch for 2 which has been tested.  4) is pretty hard
> to do in practice as you have to basically decompress into RAM when
> reading the core to do anything useful as opposed to a format that
> only compressed certain parts (e.g. if the page tables were not
> compressed only the payload in a minidump, and if it were compressed
> on some kind of block boundaries so that you could locate a given
> block and decompress it when reading specific data).  Coming up with
> such a format would be more useful but requires more work.

That patch looks ok to me, FWIW.  As I pointed out, it's easy enough to
just disable crashinfo if one doesn't want the extraction to take place.