linux-kernel - Re: linux-next: add utrace tree

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Date:	Mon, 25 Jan 2010 12:42:22 -0800 (PST)
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Mark Wielaard <mjw@...hat.com>
cc:	"Frank Ch. Eigler" <fche@...hat.com>,
	Stephen Rothwell <sfr@...b.auug.org.au>,
	Kyle Moffett <kyle@...fetthome.net>, tytso@....edu,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Peter Zijlstra <peterz@...radead.org>,
	Fr??d??ric Weisbecker <fweisbec@...il.com>,
	Oleg Nesterov <oleg@...hat.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	linux-next@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>, utrace-devel@...hat.com
Subject: Re: linux-next: add utrace tree

On Mon, 25 Jan 2010, Mark Wielaard wrote:
> 
> And all these users have wishes to extend the current ptrace interface
> mess. But nobody dares to extend ptrace in any direction because
> fixing/cleaning up one of these use cases might break the others in
> subtle and not so subtle ways. Which is why the utrace series of patches
> is cleaning up all this stuff first.

I call bullshit.

You can clean up ptrace without introducing odd new interfaces and trying 
to sell it as some revolutionary new kernel interface that can do 
anything.

I also call bullshit on the "ptrace() is so horribly nasty" argument. Yes, 
I've seen the code that uses ptrace in user space, and yes, it's nasty, 
but it's invariably _not_ nasty so much because ptrace itself is nasty, 
but because it's full of #ifdef so-and-so-os/so-and-so-arch, and the code 
is never cleaned up.

There are a couple of obvious cases of ptrace being uglier-than-it-needs- 
to-be. Like the traditional ptrace read/write interface being purely "word 
at a time", and that clearly is not pretty. Several architectures already 
do "copy range" kind of versions on it, though, so that's just a detail, 
and if anybody wanted to clean it up, they could have.

The more fundamental problem is the use of signals (while at the same time 
wanting to _trap_ non-ptrace signals), without any model for a "connection 
state", which is why you can have only one tracer. But again, that's 
largely a user interface issue, and apparently utrace does _nothing_ for 
that problem at all.

So I do agree that ptrace is not a great interface. However: repeating 
that statement over and over in _no_ way excuses some totally unrelated 
code that doesn't have anything what-so-ever to do with the actual 
problems of ptrace.

		Linus
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