From owner-freebsd-hackers  Mon Jan 29  8:58: 5 2001
Delivered-To: freebsd-hackers@freebsd.org
Received: from iguana.aciri.org (iguana.aciri.org [192.150.187.36])
	by hub.freebsd.org (Postfix) with ESMTP id 2B16737B69C
	for <hackers@FreeBSD.ORG>; Mon, 29 Jan 2001 08:57:45 -0800 (PST)
Received: (from rizzo@localhost)
	by iguana.aciri.org (8.11.1/8.11.1) id f0TGveG33419;
	Mon, 29 Jan 2001 08:57:40 -0800 (PST)
	(envelope-from rizzo)
From: Luigi Rizzo <rizzo@aciri.org>
Message-Id: <200101291657.f0TGveG33419@iguana.aciri.org>
Subject: Re: [kernel patch] fcntl(...) to close many descriptors
In-Reply-To: <4.3.0.20010129151413.023e03a0@pop.free.fr> from mouss at "Jan 29, 2001  3:17:22 pm"
To: usebsd@free.fr (mouss)
Date: Mon, 29 Jan 2001 08:57:40 -0800 (PST)
Cc: rizzo@aciri.org, drosih@rpi.edu, hackers@FreeBSD.ORG,
	wollman@khavrinen.lcs.mit.edu
X-Mailer: ELM [version 2.4ME+ PL43 (25)]
MIME-Version: 1.0
Content-Type: text/plain; charset=US-ASCII
Content-Transfer-Encoding: 7bit
Sender: owner-freebsd-hackers@FreeBSD.ORG
Precedence: bulk
X-Loop: FreeBSD.ORG

hi,
i have to admit i am not too much into theory of hashing, but i am
unclear on how a perfect hash function can be simpler than "the
obvious method" when the namespace is changing dynamically because
modules are added or deleted.
(the obvious method would be a cheap hash on 2-4 chars of
the name followed by a scan of the list in each hash slot.)

Hopefully the number of functions using this method is
small enough not to worry about the depth of the lists,
and the type of calls using this method is one where the amt
of work in the syscall itself is way larger than the matching cost.

	cheers
	luigi

> >         generic_syscall("fdcloseall", ....);
> >
> >In this way it would be clear what the non-portable pieces of code
> >are, and the mechanism would be extensible with no changes to
> >libraries and syscalls. You could even have dynamically-loaded
> >modules implementing new "syscalls".
> 
> I see a meachanism like
>          new_syscall(str, args) = syscall(hash(str), args)
> where hash() is chosen to guarantee unicity (that wouldn't be hard to find).
> we then have both performance (working with indexes instead of comparing
> strings) like what is currently available, and the flexibility of strings.
> 
> Note that this goes in the same dynamic "wind" than loadable modules and
> the like: static gets old...
> 
> 
> cheers,
> mouss


To Unsubscribe: send mail to majordomo@FreeBSD.org
with "unsubscribe freebsd-hackers" in the body of the message