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

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Message-Id: <1238491062.28248.2046.camel@twins>
Date:	Tue, 31 Mar 2009 11:17:42 +0200
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
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 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 ;-)

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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