linux-kernel - Re: [Drbd-dev] [PATCH -next] drbd: trace depends on TRACING

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Date:	Wed, 30 Sep 2009 10:02:21 +0200
From:	Lars Ellenberg <lars.ellenberg@...bit.com>
To:	Christoph Hellwig <hch@...radead.org>
Cc:	Philipp Reisner <philipp.reisner@...bit.com>,
	Randy Dunlap <randy.dunlap@...cle.com>,
	Stephen Rothwell <sfr@...b.auug.org.au>,
	LKML <linux-kernel@...r.kernel.org>, linux-next@...r.kernel.org,
	akpm <akpm@...ux-foundation.org>, drbd-dev@...ts.linbit.com
Subject: Re: [Drbd-dev] [PATCH -next] drbd: trace depends on TRACING

On Tue, Sep 29, 2009 at 11:37:47AM -0400, Christoph Hellwig wrote:
> On Tue, Sep 29, 2009 at 05:32:50PM +0200, Philipp Reisner wrote:
> > On Saturday 26 September 2009 01:03:04 Randy Dunlap wrote:
> > > From: Randy Dunlap <randy.dunlap@...cle.com>
> > >
> > > DRBD_TRACE should depend on TRACING.
> > > It's also possible that TRACEPOINTS should depend on TRACING.
> > >
> > 
> > Hi Randy,
> > 
> > I tried to figure out in which way that should be done. By looking
> > at "BLK_DEV_IO_TRACE" I got the impression that this should
> > be done by adding "select GENERIC_TRACER".
> 
> Neither really.  The only way of tracing that should be used is the
> TRACE_EVENT macros, which compile away to nothing if tracing is
> disabled, so no dependency is needed at all.

TRACE_EVENT macros depend on, and use TRACE_POINTS.
And those trace points are what compiles away if !CONFIG_TRACEPOINTS, no?

kernel/trace/Kconfig says
# All tracer options should select GENERIC_TRACER. [...]

If one uses tracepoints without trace_events, they still compile away.

If using tracepoints directly, not using the (admittedly elegant)
trace-events macro system, is in fact not wanted anymore, then
Documentation/trace/* should be changed accordingly.

So what is the plan, going forward?

-- 
: Lars Ellenberg
: LINBIT | Your Way to High Availability
: DRBD/HA support and consulting http://www.linbit.com

DRBD® and LINBIT® are registered trademarks of LINBIT, Austria.
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