linux-kernel - Re: [PATCH 0/3] ftrace: overrun accounting and trace

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Date:	Tue, 22 Apr 2008 20:58:15 -0400 (EDT)
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Pekka Paalanen <pq@....fi>
cc:	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...e.hu>,
	akpm@...l.org, Peter Zijlstra <peterz@...radead.org>,
	Soeren Sandmann Pedersen <sandmann@...hat.com>
Subject: Re: [PATCH 0/3] ftrace: overrun accounting and trace_pipe headers


On Tue, 22 Apr 2008, Pekka Paalanen wrote:

> Excellent!

Thanks ;-)

>
> On Mon, 21 Apr 2008 17:09:35 -0400
> Steven Rostedt <rostedt@...dmis.org> wrote:
>
> > The first patch in this series adds accounting to record overruns. That is
> > where the writing catches up to the reading of the buffer. This really
> > only matters for trace_pipe since that's a consumer / producer output file.
>
> This takes me some thinking how to make the best of it, but looks like it
> allows me to relay the overrun events into the trace log. Very good.
>
> > The next patch adds new methods for the plugins to hook into the
> > open_pipe and open_read, to let a plugin produce a header.
> > The open_read method can also be used to do something when overruns
> > are detected.
>
> You mean pipe_open() and read()? :-)
> And read() is pipe specific?

Yeah the read API is pipe specific (for now). I'll have to think about
whether or not we should have a generic "read" and a "pipe_read"

> Ah, now I see what you mean by read() can be used to notice overruns:
> it is called for every read syscall, not just in the beginning.

Right!

>
> > The last patch is a test patch AND SHOULD NOT BE APPLIED. It is just an
> > example in how to use the new methods to produce a header. It simply
> > makes the ftrace tracer produce a simple "Test header" before any
> > output.
>
> In function_read(), shouldn't I be doing something with filp and/or ppos?

Probably, that's why I said not to apply it ;-)

Thanks,

-- Steve

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