linux-kernel - Re: CONFIG

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Date:	Wed, 23 Jan 2008 09:48:12 -0500
From:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
To:	"Frank Ch. Eigler" <fche@...hat.com>
Cc:	Jon Masters <jcm@...hat.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Rusty Russell <rusty@...tcorp.com.au>,
	Christoph Hellwig <hch@...radead.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: CONFIG_MARKERS

* Frank Ch. Eigler (fche@...hat.com) wrote:
> Hi -
> 
> On Tue, Jan 22, 2008 at 11:17:40PM -0500, Jon Masters wrote:
> > On Tue, 2008-01-22 at 22:10 -0500, Mathieu Desnoyers wrote:
> > > [...]
> > > > > Is this an attempt to not set a marker for proprietary modules? [...]
> > > > 
> > > > I can't seem to find any discussion about this aspect.  If this is the
> > > > intent, it seems misguided to me.  There may instead be a relationship
> > > > to TAINT_FORCED_{RMMOD,MODULE}.  Mathieu?
> 
> > > On my part, its mostly a matter of not crashing the kernel when someone
> > > tries to force modprobe of a proprietary module (where the checksums
> > > doesn't match) on a kernel that supports the markers. Not doing so
> > > causes the markers to try to find the marker-specific information in
> > > struct module which doesn't exist and OOPSes.
> 
> But you have the wrong target: it is not proprietary modules that have
> this risk but those built out-of-tree without checksums.  Maybe
> oopsing in this case is not so bad; or the check could just limit itself to
> FORCED_MODULE.
> 

I guess that for this one I could have a :

if (!mod->taints & TAINT_FORCED_MODULE)
 ...


> 
> > > Christoph's point of view is rather more drastic than mine : it's not
> > > interesting for the kernel community to help proprietary modules writers,
> > > so it's a good idea not to give them marker support. (I CC'ed him so he
> > > can clarify his position).
> > Right. I thought that was your collective opinion
> 
> Another way of looking at this though is that by allowing/encouraging
> proprietary module writers to include markers, we and their users get
> new diagnostic capabilities.  It constitutes a little bit of opening
> up, which IMO we should reward rather than punish.
> 
> 

This specific one is a kernel policy matter, and I personally don't
have a strong opinion about it. I agree that you raise a good counter
argument : it can be useful to proprietary modules users to be able to
extract tracing information from those modules to argue with their
vendors that their driver/hardware is broken (a tracer is _very_ useful
in that kind of situation). However, it is also useful to proprieraty
module writers who can benefit from the merged kernel/modules traces.
Do we want to give them this ability ? It would surely help writing
better proprieraty kernel modules. Do we want this, or rather prefer to
put more pressure on them so they open their code ?

I will let others fight in the mud on this one. :)

for this one, we could add, instead :

if (!mod->taints & (TAINT_FORCED_MODULE | TAINT_PROPRIETARY_MODULE))

Mathieu

> - FChE

-- 
Mathieu Desnoyers
Computer Engineering Ph.D. Student, Ecole Polytechnique de Montreal
OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F  BA06 3F25 A8FE 3BAE 9A68
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