linux-kernel - Re: [PATCH -v2] ftrace: Documentation

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Date:	Mon, 14 Jul 2008 21:43:46 -0400 (EDT)
From:	Steven Rostedt <rostedt@...dmis.org>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Randy Dunlap <randy.dunlap@...cle.com>,
	Elias Oltmanns <eo@...ensachen.de>,
	LKML <linux-kernel@...r.kernel.org>, Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>,
	Peter Zijlstra <peterz@...radead.org>,
	Clark Williams <clark.williams@...il.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Jon Masters <jonathan@...masters.org>
Subject: Re: [PATCH -v2] ftrace: Documentation


On Mon, 14 Jul 2008, Eric W. Biederman wrote:

>
> Steven Rostedt <rostedt@...dmis.org> writes:
>
> > Actually it is a /debug (or /sys/mount/debug if you prefer) file.
>
> Got it.  I haven't ever actually seen anyone use debugfs.
>
> > I'd be interested in knowing who would want namespaces in traces. I've
> > basically only used tracing to see "what's happening in the kernel here?".
> > Where I only use the pid to differentiate between the tasks I know are
> > running.
>
> > Hence, tracing is much like printk. Does it really matter with these
> > outputs. But ftrace is pluggable, pid namespaces may matter in future
> > plugins.

Bare with me, I'm new to the namespace concept of pids.

>
> So it would not be hard to capture the pid namespace in mount or
> even look at current to get it (although the last is a little odd).

>From userspace or from with the kernel (doing the trace)

>
> I'm not at all certain if it makes sense.  If this is something
> an ordinary user could use then we definitely want to do something.
>
> Is tracing possible without inserting kernel modules?

The tracer is built into the kernel (no module needed).

-- Steve

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