From owner-freebsd-arch  Thu Jan  4 15:52:58 2001
From owner-freebsd-arch@FreeBSD.ORG  Thu Jan  4 15:52:55 2001
Return-Path: <owner-freebsd-arch@FreeBSD.ORG>
Delivered-To: freebsd-arch@freebsd.org
Received: from fw.wintelcom.net (ns1.wintelcom.net [209.1.153.20])
	by hub.freebsd.org (Postfix) with ESMTP id B39F937B400
	for <arch@FreeBSD.ORG>; Thu,  4 Jan 2001 15:52:55 -0800 (PST)
Received: (from bright@localhost)
	by fw.wintelcom.net (8.10.0/8.10.0) id f04Nqli13376;
	Thu, 4 Jan 2001 15:52:47 -0800 (PST)
Date: Thu, 4 Jan 2001 15:52:47 -0800
From: Alfred Perlstein <bright@wintelcom.net>
To: Tony Finch <dot@dotat.at>
Cc: arch@FreeBSD.ORG
Subject: Re: Reinstatement of CIRCLEQ
Message-ID: <20010104155247.G292@fw.wintelcom.net>
References: <20010104001943.T292@fw.wintelcom.net> <200101041708.JAA05731@beastie.mckusick.com> <20010104222519.Y2140@hand.dotat.at> <20010104154404.F292@fw.wintelcom.net>
Mime-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
User-Agent: Mutt/1.2.5i
In-Reply-To: <20010104154404.F292@fw.wintelcom.net>; from bright@wintelcom.net on Thu, Jan 04, 2001 at 03:44:04PM -0800
Sender: bright@fw.wintelcom.net
Sender: owner-freebsd-arch@FreeBSD.ORG
Precedence: bulk
X-Loop: FreeBSD.ORG

* Alfred Perlstein <bright@wintelcom.net> [010104 15:44] wrote:
> * Tony Finch <dot@dotat.at> [010104 14:25] wrote:
> > Kirk McKusick <mckusick@mckusick.com> wrote:
> > >	From: Alfred Perlstein <bright@wintelcom.net>
> > >
> > >	You're right, I'm wondering though, would it be possible
> > >	to change TAILQ_PREV(elm, headname, field) to TAILQ_PREV(elm,
> > >	field) by using the offset of 'field' into the struct?
> > >	You could subtract the offset of 'field' from the tqe_prev
> > >	of the next struct right?
> > >
> > >You are correct that your suggested change is exactly the
> > >unportability/headache that I am trying to avoid.
> > 
> > The Apache Group needed a linked list structure that would allow
> > insertions before and after a given element without knowing the
> > address of the list header. Although I wanted to use sys/queue.h it
> > didn't quite have that functionality so I wrote some "ring" macros
> > based on code by Dean Gaudet.
> 
> Why not just use "LIST" then?

Oh, actually for TAILQ one doesn't need the listhead, just a dummy
struct declaration:

TAILQ_HEAD(wizbangheadp, wizbang);

which expands to this:

struct wazbangheadp {
        struct wizbang *tqh_first;
        struct wizbang **tqh_last;
}

TAILQ_PREV then just needs these args:

TAILQ_PREV(&mywizbang, -> wazbangheadp <-, field);

---------------------------^^^

just the struct name.

Yes, it's icky and it's C's fault for not having "typeof()" in
the standard.

-- 
-Alfred Perlstein - [bright@wintelcom.net|alfred@freebsd.org]
"I have the heart of a child; I keep it in a jar on my desk."


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