[PATCH] drm: Funnel drm logs to tracepoints

[Pekka Paalanen]

On Tue, 3 Dec 2019 22:20:14 +0100
Daniel Vetter <daniel.vetter at ffwll.ch> wrote:

> On Tue, Dec 3, 2019 at 8:10 PM Sean Paul <sean at poorly.run> wrote:
> >
> > On Thu, Oct 17, 2019 at 10:22:16AM +0300, Pekka Paalanen wrote:  
> > > On Wed, 16 Oct 2019 15:23:45 +0200
> > > Thomas Zimmermann <tzimmermann at suse.de> wrote:
> > >  
> > > > Hi
> > > >
> > > > Am 16.10.19 um 15:05 schrieb Pekka Paalanen:  
> > >  
> > > > > specifically be available in production. So a new file in some fs
> > > > > somewhere it should be, and userspace in production can read it at will
> > > > > to attach to a bug report.
> > > > >
> > > > > Those semantics, "only use this content for attaching into a bug
> > > > > report" should be made very clear in the UAPI.  
> > > >
> > > > Has this ever worked? As soon as a userspace program starts depending on
> > > > the content of this file, it becomes kabi. From the incidents I know,
> > > > Linus has always been quite strict about this. Even for broken interfaces.  
> > >
> > > The kernel log content is not kabi, is it? I've seen it change plenty
> > > during the years. This would be just another similar log with free-form
> > > text.
> > >  
> >
> > Ok, so given the more structured version of this set [1] was not well received,
> > are we all comfortable going with the freeform approach in this version?  
> 
> Imo yes. It's still uabi, so someone will have regrets about it. But
> given that dmesg has been around forever, and causes rather little
> breakage, I think we should be fairly ok.
> 
> I still think that figuring out the drm_dev logging bikeshed might be
> good, while we noodle around in here.

Hi,

one more wacky idea: have a flight recorder buffer(s) in the kernel,
but do not expose them as is to userspace. Instead, create a trigger
somewhere (/proc?) that causes the flight recorder buffers to be
flushed into dmesg. That way the amount of new UABI is reduced to just
the trigger. Obviously this spams dmesg and would need the rights to
access dmesg to actually collect the logs. I'm not sure if that's good
or bad, but it would re-use dmesg.


Thanks,
pq
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