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Date: Wed, 4 Mar 2009 13:12:59 +0100
From: Frederic Weisbecker <fweisbec@gmail.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Ingo Molnar <mingo@elte.hu>, Steven Rostedt <rostedt@goodmis.org>,
       =?iso-8859-1?B?VPZy9ms=?= Edwin <edwintorok@gmail.com>,
       Jason Baron <jbaron@redhat.com>, lkml <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH -v2] tracing: lockdep tracepoints
Message-ID: <20090304121258.GD6032@nowhere>
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On Wed, Mar 04, 2009 at 12:58:03PM +0100, Peter Zijlstra wrote:
> On Wed, 2009-03-04 at 12:43 +0100, Ingo Molnar wrote:
> > 
> > > +TRACE_FORMAT(lock_contended,
> > > +     TPPROTO(struct lockdep_map *lock, unsigned long ip),
> > > +     TPARGS(lock, ip),
> > > +     TPFMT("%s", lock->name)
> > > +     );
> > 
> > Would it be possible to use the C syntax tracepoints perhaps? 
> > They are bigger:
> > 
> >      TRACE_EVENT_FORMAT(sched_switch,
> >         TPPROTO(struct rq *rq, struct task_struct *prev,
> >                 struct task_struct *next),
> >         TPARGS(rq, prev, next),
> >         TPFMT("task %s:%d ==> %s:%d",
> >               prev->comm, prev->pid, next->comm, next->pid),
> >         TRACE_STRUCT(
> >                 TRACE_FIELD(pid_t, prev_pid, prev->pid)
> >                 TRACE_FIELD(int, prev_prio, prev->prio)
> >                 TRACE_FIELD_SPECIAL(char next_comm[TASK_COMM_LEN],
> >                                     next_comm,
> >                                     TPCMD(memcpy(TRACE_ENTRY->next_comm,
> >                                                  next->comm,
> >                                                  TASK_COMM_LEN)))
> >                 TRACE_FIELD(pid_t, next_pid, next->pid)
> >                 TRACE_FIELD(int, next_prio, next->prio)
> >         ),
> >         TPRAWFMT("prev %d:%d ==> next %s:%d:%d")
> >         );
> 
> I'm not quite sure how to do strings with those. The IRQ tracepoints
> cheat and omit the string, and the sched tracepoints cheat and use this
> static sized comm array.
> 


The TRACE_FIELD_SPECIAL is only used in case of complex assignment,
those that can't be done in a simple "=" expression.

All you need is simply:

TRACE_FORMAT(lock_contended,
     TPPROTO(struct lockdep_map *lock, unsigned long ip),
     TPARGS(lock, ip),
     TPFMT("%s", lock->name)
     TRACE_STRUCT(
	TRACE_FIELD(char *, name, lock->name)
     )
     TPRAWFMT("%s");
);

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