linux-kernel - Re: [GIT PULL] tracing: make signal tracepoints more useful

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Message-ID: <20120118115938.GA14863@elte.hu>
Date:	Wed, 18 Jan 2012 12:59:38 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	Steven Rostedt <rostedt@...dmis.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Ingo Molnar <mingo@...hat.com>,
	Masami Hiramatsu <mhiramat@...hat.com>,
	Seiji Aguchi <saguchi@...hat.com>,
	linux-kernel@...r.kernel.org,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
Subject: Re: [GIT PULL] tracing: make signal tracepoints more useful


* Oleg Nesterov <oleg@...hat.com> wrote:

> On 01/17, Ingo Molnar wrote:
> >
> > Any tool that requests the signal trace event, and copies 
> > the full (and now larger) record it got in the ring-buffer, 
> > without expanding the target record's size accordingly will 
> > *BREAK*.
> >
> > I do not claim that tools will break in practice - i'm 
> > raising the *possibility* out of caution and i'm frustrated 
> > that you *STILL* don't understand how ABIs are maintained in 
> > Linux.
> 
> OK, but what if we rename the tracepoint?
> 
> IOW, add the new tracepoint and remove the old one. Of course, 
> this can confuse the users of the current "signal_generate", 
> but this is safe. b413d48a does this...
> 
> Or this is not allowed too?

Everything is allowed that makes sense and does not break apps, 
with a strong preference towards the simplest possible variant.

I.e. your patch.

Thanks,

	Ingo
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