linux-kernel - Re: [PATCH 3/3] utrace-based ftrace "process" engine, v2

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Date:	Tue, 31 Mar 2009 13:27:56 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Theodore Tso <tytso@....edu>, oleg@...hat.com, adobriyan@...il.com,
	mingo@...e.hu, torvalds@...ux-foundation.org, fche@...hat.com,
	roland@...hat.com, rostedt@...dmis.org, utrace-devel@...hat.com,
	linux-kernel@...r.kernel.org, tglx@...utronix.de,
	Christoph Hellwig <hch@...radead.org>,
	Jeff Dike <jdike@...toit.com>
Subject: Re: [PATCH 3/3] utrace-based ftrace "process" engine, v2

On Tue, 2009-03-31 at 11:17 +0200, Peter Zijlstra wrote:
> On Mon, 2009-03-30 at 15:18 -0700, Andrew Morton wrote:
> > So we need to work out what to do about utrace and I feel a need to hit
> > the reset button on all this.  Largely because I've forgotten
> > everything and it was all confusing anyway.
> 
> Right, from my POV something like utrace is desirable, since its
> basically a huge multiplexer for the debugger state, eventually allowing
> us to have multiple debuggers attached to the same process.
> 
> So in that respect its a very nice feature.
> 
> > Could those who object to utrace please pipe up and summarise their
> > reasons?
> 
> Christoph used to have an opinion on this matter, so I've added him to
> the CC.
> 
> Last time when I looked at the code, it needed a bit more care and
> comments wrt lifetimes and such. I know Roland has done a lot on that
> front -- so I'll need to re-inspect.
> 
> As to in-kernel users, currently we only have ptrace, and no full
> conversion to utrace is in a mergeable shape afaik.
> 
> UML (Jeff CC'ed) might want to use this.
> 
> I know the Systemtap people need this (fche). But that isn't really
> moving towards mainline any time soon afaict.
> 
> Then there is this little thing called frysk which uses it, no idea what
> kind of kernel space that needs, nor where it lives -- or for that
> matter, wth it really does ;-)

And Frank reminded me we have an ftrace tracer that utilizes utrace.

> Anyway, long story short, once people have had a little time to go over
> the code, and a few in-kernel users are lined-up, I think we should
> consider merging it.
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