linux-kernel - Re: [PATCH v10 04/12] tracing: Add 'snapshot' event trigger command

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Date:	Fri, 11 Oct 2013 09:04:28 -0500
From:	Tom Zanussi <tom.zanussi@...ux.intel.com>
To:	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
Cc:	rostedt@...dmis.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v10 04/12] tracing: Add 'snapshot' event trigger command

On Fri, 2013-10-11 at 22:47 +0900, Masami Hiramatsu wrote:
> (2013/10/11 9:48), Tom Zanussi wrote:
> >  /**
> > + * tracing_alloc_snapshot - allocate snapshot buffer.
> > + *
> > + * This only allocates the snapshot buffer if it isn't already
> > + * allocated - it doesn't also take a snapshot.
> > + *
> > + * This is meant to be used in cases where the snapshot buffer needs
> > + * to be set up for events that can't sleep but need to be able to
> > + * trigger a snapshot.
> > + */
> > +int tracing_alloc_snapshot(void)
> > +{
> > +	struct trace_array *tr = &global_trace;
> > +	int ret;
> > +
> > +	ret = alloc_snapshot(tr);
> > +	WARN_ON(ret < 0);
> > +
> > +	return ret;
> > +}
> > +EXPORT_SYMBOL_GPL(tracing_alloc_snapshot);
> 
> Out of curiously, why this symbol is exported to modules?
> The functions which are called directly from trace_event macros
> should be exported because those macros can be used in module code,
> but I couldn't find this in such code, at a glance.
> 

tracing_alloc_snapshot() goes along with tracing_snapshot() and
tracing_snapshot_alloc() which are already exported - you should be able
to take a snapshot from a module, or do a combined snapshot/alloc or
(now) just the alloc.

Tom

> Thank you,
> 
> 
> 


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