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Date: Tue, 31 Oct 2006 22:39:06 +0000
From: Al Viro <viro@ftp.linux.org.uk>
To: Valdis.Kletnieks@vt.edu
Cc: Dave Jones <davej@redhat.com>, ray-gmail@madrabbit.org,
       "Martin J. Bligh" <mbligh@google.com>,
       Linus Torvalds <torvalds@osdl.org>, Andrew Morton <akpm@osdl.org>,
       Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
       "Jun'ichi Nomura" <j-nomura@ce.jp.nec.com>
Subject: Re: Linux 2.6.19-rc4
Message-ID: <20061031223906.GR29920@ftp.linux.org.uk>
References: <Pine.LNX.4.64.0610302019560.25218@g5.osdl.org> <20061030213454.8266fcb6.akpm@osdl.org> <Pine.LNX.4.64.0610310737000.25218@g5.osdl.org> <45477668.4070801@google.com> <2c0942db0610310834i6244c0abm10c81e984565ed8a@mail.gmail.com> <20061031165133.GB23354@redhat.com> <200610312126.k9VLQtCB003616@turing-police.cc.vt.edu>
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On Tue, Oct 31, 2006 at 04:26:55PM -0500, Valdis.Kletnieks@vt.edu wrote:
> On Tue, 31 Oct 2006 11:51:33 EST, Dave Jones said:
> > On Tue, Oct 31, 2006 at 08:34:23AM -0800, Ray Lee wrote:
> >  > On 10/31/06, Martin J. Bligh <mbligh@google.com> wrote:
> >  > > > At some point we should get rid of all the "politeness" warnings, just
> >  > > > because they can end up hiding the _real_ ones.
> >  > >
> >  > > Yay! Couldn't agree more. Does this mean you'll take patches for all the
> >  > > uninitialized variable crap from gcc 4.x ?
> >  > 
> >  > What would be useful in the short term is a tool that shows only the
> >  > new warnings that didn't exist in the last point release.
> > 
> > git clone git://git.kernel.org/pub/scm/linux/kernel/git/viro/remapper.git
> 
> As somebody proves me wrong on the fact it's not easy.  Of course, it's
> Al's git tree, which is probably saying something. :)

It is easy, actually.  Key observation: unidiff with 0 context lines contains
everything you need to find out which lines survive and where do they move;
just ignore the actual changes in the diff and look at @@... and diff headers.
There are two parts - one takes such diff and generates a fate map for lines
(basically, "this range gets shifted to this place, this range doesn't make it
at all" + file removals + file renames if diff has been generated by git-diff
and contains that information).  Another is a very simple filter; it takes
map file as argument, reads it and uses the map to massage lines it reads
from stdin.  When we see <affected pathname>:<number> in the beginning of the
line or after a space, see if that line is in surviving range; if it is,
replace pathname and shift line number, otherwise add a prefix ("O:" by
default).  That's it.  About 10K of sparse C - both filter and map generator.

	Two-clause BSD license, so feel free to use it in any way you want.
I don't think there will be serious changes down the road; I'll need to
sit down and turn a description of that puppy into a proper manpage, but
that's about it.
-
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