Date: Thu, 26 Nov 2009 13:24:41 +0100
From: Ingo Molnar <mingo@elte.hu>
To: Christoph Hellwig <hch@infradead.org>
Cc: Oleg Nesterov <oleg@redhat.com>, Alexey Dobriyan <adobriyan@gmail.com>,
       Ananth Mavinakayanahalli <ananth@in.ibm.com>,
       "Frank Ch. Eigler" <fche@redhat.com>,
       Peter Zijlstra <peterz@infradead.org>,
       Roland McGrath <roland@redhat.com>, linux-kernel@vger.kernel.org,
       utrace-devel@redhat.com
Subject: Re: [RFC,PATCH 0/14] utrace/ptrace
Message-ID: <20091126122441.GC15189@elte.hu>
References: <20091124200127.GA5751@redhat.com>
 <20091125214818.GA4916@infradead.org>
 <20091126091052.GF1389@elte.hu>
 <20091126104722.GA8316@infradead.org>
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* Christoph Hellwig <hch@infradead.org> wrote:

> On Thu, Nov 26, 2009 at 10:10:52AM +0100, Ingo Molnar wrote:
> > > [...]  Given that's it's pretty much too later for the 2.6.33 cycle 
> > > anyway I'd suggest you make sure the remaining two major architectures 
> > > (arm and mips) get converted, and if the remaining minor architectures 
> > > don't manage to get their homework done they're left without ptrace.
> > 
> > I suspect the opinion of the ptrace maintainers matters heavily whether 
> > it's appropriate for v2.6.33. You are not going to maintain this, they 
> > are.
> 
> I am whoever like many others going to use it.  And throwing in new 
> code a few days before the merge window closes [...]

FYI, the merge window has not opened yet, so it cannot close in a few 
days.

> [...] and thus not getting any of the broad -next test coverage is a 
> pretty bad idea.  In the end it will be the maintainers ruling but 
> that doesn't make it a good idea from the engineering point of view.

FYI, it's been in -mm, that's where it's maintained.

> > Regarding porting it to even more architectures - that's pretty much 
> > the worst idea possible. It increases maintenance and testing 
> > overhead by exploding the test matrix, while giving little to end 
> > result. Plus the worst effect of it is that it becomes even more 
> > intrusive and even harder (and riskier) to merge.
> 
> But it doesn't.  Take a look at what these patches actually do, they 
> basically introduce a new utrace layer, and (conditionally) rewrite 
> ptrace to use it.  The arch support isn't actually part of these 
> patches directly but rather the cleanup of the underlying arch ptrace 
> code to use regsets, tracehooks and co so that the new ptrace code can 
> use.

( I am aware of its design, i merged the original tracehook patches for 
  x86. )

> What the patches in the current form do is to introduce two different 
> ptrace implementations, with one used on the architectures getting 
> most testing and another secondary one for left over embedded or dead 
> architectures with horrible results.  So removing the old one is much 
> better.  The arm ptrace rewrite has already been posted by Roland, btw 
> including some feedback from Russell, but nothing really happened to 
> it.

Yes. Which is a further argument to not do it like that but to do one 
arch at a time. Trying to do too much at once is bad engineering.

	Ingo
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