linux-kernel - Re: Q: tracing: can we change trace_signal

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Date:	Mon, 21 Nov 2011 21:21:10 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	Frederic Weisbecker <fweisbec@...il.com>,
	Ingo Molnar <mingo@...hat.com>, Jiri Olsa <jolsa@...hat.com>,
	Masami Hiramatsu <mhiramat@...hat.com>,
	Seiji Aguchi <saguchi@...hat.com>, linux-kernel@...r.kernel.org
Subject: Re: Q: tracing: can we change trace_signal_generate() signature?

On 11/21, Steven Rostedt wrote:
>
> On Mon, 2011-11-21 at 20:19 +0100, Oleg Nesterov wrote:
> > Hello,
> >
> > Is it possible to change trace_signal_generate()'s args or this
> > is the part of the kernel ABI?
>
> As Linus said. It's only part of the ABI if a tool is using it. If you
> change it and no one complains, then it should be good to go.

I only I knew if it is used (and how) or not...

> > IOW. Ignoring the changes in include/trace/events/signal.h,
> > can the patch below work or the changes like this are not
> > allowed?
>
> I say change it and see who screams.

Heh. How can I do this? The only thing I can do is: send the patch
to the maintainer - you ;)

OK. I'll send the patch "officially" tomorrow, let's see who nacks it.

> > +enum {
> > +	TRACE_SIGNAL_DELIVERED,
> > +	TRACE_SIGNAL_IGNORED_OR_BLOCKED,

(can't understand why I added _OR_BLOCKED, it should be
 TRACE_SIGNAL_IGNORED)

> > @@ -1095,14 +1106,15 @@ static int __send_signal(int sig, struct siginfo *info, struct task_struct *t,
> >  			 * signal was rt and sent by user using something
> >  			 * other than kill().
> >  			 */
> > -			trace_signal_overflow_fail(sig, group, info);
> > -			return -EAGAIN;
> > +			result = TRACE_SIGNAL_OVERFLOW_FAIL;
> > +			ret = -EAGAIN;
> > +			goto ret;
> >  		} else {
> >  			/*
> >  			 * This is a silent loss of information.  We still
> >  			 * send the signal, but the *info bits are lost.
> >  			 */
> > -			trace_signal_lose_info(sig, group, info);
> > +			result = TRACE_SIGNAL_LOSE_INFO;
> 
> Hmm, all this result manipulation added for tracing that doesn't occur
> in 99.99% of all machines?

Not sure I understand...

With this patch trace_signal_generate() also reports "result" which
allows to know was the signal actually delivered or not. And, if not,
why it wasn't delivered.

TRACE_SIGNAL_OVERFLOW_FAIL and TRACE_SIGNAL_LOSE_INFO are not really
needed, but this way we can kill trace_signal_overflow_fail() and
trace_signal_lose_info() and simplify the code.

Oleg.

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