linux-kernel - Re: [PATCH] ftrace: add an fsync tracer

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Message-ID: <20081106131348.68f8858e@infradead.org>
Date:	Thu, 6 Nov 2008 13:13:48 -0800
From:	Arjan van de Ven <arjan@...radead.org>
To:	fche@...hat.com (Frank Ch. Eigler)
Cc:	Steven Rostedt <rostedt@...dmis.org>,
	Peter Zijlstra <peterz@...radead.org>,
	linux-kernel@...r.kernel.org, mingo@...e.hu, alan@...hat.com,
	jbaron@...hat.com
Subject: Re: [PATCH] ftrace: add an fsync tracer

On Thu, 06 Nov 2008 15:19:48 -0500
fche@...hat.com (Frank Ch. Eigler) wrote:

> Arjan van de Ven <arjan@...radead.org> writes:
> 
> > [...]
> > what is the real need is
> > 1) Have a trace point in the source
> > 2) Associate a "formatting function" with that point 
> >    (which basically transforms the trace parameters to, say, a
> > string) 3) A way to turn the trace point on/off.
> 
> For 1 and 2, it may be worth considering a plain trace_mark() in
> do_sync().  The complication that makes this uglier than a one-liner

no why is that?

what you really need is to be able to provide a callback function
pointer that will do the formatting,
or as Peter wants it, a format string.

(and we can easily make a format string that knows how to print a
struct file, no big deal, I suspect that is a common thing actually)

Doing this like you propose is just too complex and too specialistic;
the reality is that merely formatting the arguments of a trace point is
the common case, and I suspect for 99.9% of the cases we can get away
with a standard default formatting.

We should make THAT easy. Not complex or ugly. But easy.

And then if I or some tool wants to see a tracepoint, we have some
standard way to enumerate them and turn individual ones on with their
standard formatting ... and that's it.
no iffs or buts

-- 
Arjan van de Ven 	Intel Open Source Technology Centre
For development, discussion and tips for power savings, 
visit http://www.lesswatts.org
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