linux-kernel - Re: Thinking outside the box on file systems

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Date:	Sun, 19 Aug 2007 03:57:58 +0100
From:	Al Viro <viro@....linux.org.uk>
To:	david@...g.hm
Cc:	Alan <alan@...eserver.org>, Kyle Moffett <mrmacman_g4@....com>,
	Marc Perkel <mperkel@...oo.com>, Valdis.Kletnieks@...edu,
	Michael Tharp <gxti@...tiallystapled.com>,
	LKML Kernel <linux-kernel@...r.kernel.org>,
	Lennart Sorensen <lsorense@...lub.uwaterloo.ca>
Subject: Re: Thinking outside the box on file systems

On Sat, Aug 18, 2007 at 07:03:06PM -0700, david@...g.hm wrote:
> >>I suspect you will find it somewhat hard to convince *anybody* on
> >>this list to put either a regex engine or a Perl interpreter into the
> >>kernel.  I doubt you could even get a simple shell-style pattern
> >>matcher in.  First of all, both of the former chew up enormous gobs
> >>of stack space *AND* they're NP-complete.

Eh?  regex via NFA is O(expression size * string length) time and
O(expression size) space.  If you can show that regex matching is
NP-complete, you've got a good shot at Nevanlinna Prize...

Not that it made regex in kernel a good idea, but fair is fair -
unless you can show any mentioning of backrefs upthread...[1]

>  You just can't do such
> >>matching even in polynomial time, let alone something that scales
> >>appropriately for an OS kernel like, say, O(log(n)).
> >
> >Already been done.  Take a look at "AppArmor" aka "Immunix".
> 
> don't forget the ACPI interpreter.

YAProof that bogons follow Boze statistics...
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