linux-kernel - Re: move gfs2 tracepoints to inclue/trace/events dir

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Message-ID: <20091025162913.GC20391@elte.hu>
Date:	Sun, 25 Oct 2009 17:29:13 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Christoph Hellwig <hch@...radead.org>
Cc:	Steven Whitehouse <swhiteho@...hat.com>,
	Jason Baron <jbaron@...hat.com>, cluster-devel@...hat.com,
	linux-kernel@...r.kernel.org, rostedt@...dmis.org
Subject: Re: move gfs2 tracepoints to inclue/trace/events dir


* Christoph Hellwig <hch@...radead.org> wrote:

> On Mon, Oct 12, 2009 at 12:00:37PM +0200, Ingo Molnar wrote:
>
> > yeah. I have no objection to adding it to include/trace/. 
> > Tracepoints are a fundamentally global business.
> > 
> > Subsystems can opt to hide their tracepoints locally, but it's 
> > better to have a global view about what's out there, so that it can 
> > be extended coherently, etc.
> 
> We're lacking quite a bit coherence even with it.  The originally 
> reason why there were global was that the infrastructure couldn't cope 
> with having the either in modules or elsewhere in the source tree at 
> all.
> 
> We have managed to avoid global directories for drivers/filesystems 
> for as much as we can lately.  Having everything in a directory makes 
> sure it's self-contained and people don't use it accidentally from 
> other modules, which also applies to trace events - we don't want 
> people accidentally use gfs2 tracepoints from a driver (and if you 
> think that's far fetched look at the recent example of a driver using 
> debugging macros from the networking code that got pulled in 
> accidentally somewhere).

Tracepoints are closer to documentation than to filesystem 
functionality. And you are wrong when you say that everything related to 
filesystems is 'modular' - we have all documentation concentrated in 
Documentation/filesystems/ - and that is good so.

Just like we have library functions for filesystems concentrated in 
fs/*.c.

I think you are looking at it way too rigidly without considering the 
other side of the equation. Modularity has its costs: it hides details 
and makes it harder to compare implementations.

	Ingo
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