linux-kernel - Re: [PATCH] tracing: Move tracepoint callbacks into DEFINE

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Message-ID: <20090818141906.GA2669@redhat.com>
Date:	Tue, 18 Aug 2009 10:19:06 -0400
From:	Jason Baron <jbaron@...hat.com>
To:	Josh Stone <jistone@...hat.com>
Cc:	linux-kernel@...r.kernel.org, fweisbec@...il.com, mingo@...e.hu,
	laijs@...fujitsu.com, rostedt@...dmis.org, peterz@...radead.org,
	mathieu.desnoyers@...ymtl.ca, jiayingz@...gle.com,
	mbligh@...gle.com, lizf@...fujitsu.com
Subject: Re: [PATCH] tracing: Move tracepoint callbacks into DEFINE

On Tue, Aug 18, 2009 at 12:23:47AM -0700, Josh Stone wrote:
> It's not strictly correct for the tracepoint reg/unreg callbacks to
> occur when a client is hooking up, because the actual tracepoint may no
> be present yet.  This happens to be fine for syscall, since that's in
> the core kernel, but it would cause problems for tracepoints defined in
> a module that hasn't been loaded yet.  It also means the reg/unreg has
> to be EXPORTed for any modules to use the tracepoint (as in SystemTap).
> 
> This patch removes DECLARE_TRACE_WITH_CALLBACK, and instead introduces
> DEFINE_TRACE_WITH_CALLBACK which stores the callbacks in struct
> tracepoint.  The callbacks are used now when the active state of the
> tracepoint changes in set_tracepoint & disable_tracepoint.
> 
> This also introduces TRACE_EVENT_WITH_CALLBACK, so those events can also
> provide callbacks if needed.
> 

this makes sense...Ingo also suggested having the two high level
tracepoints be 'TRACE_EVENT' style. That is we should be able to
register with the syscall entry and get the *all* the syscall numbers
and arguments, and likewise on exit we should be able to get *all*
syscall exit return values. see:

http://marc.info/?l=linux-kernel&m=125008740803571&w=2 

does this patch allow/do that?

thanks,

-Jason
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