From owner-freebsd-arch@FreeBSD.ORG  Thu Apr 17 13:44:56 2008
Return-Path: <owner-freebsd-arch@FreeBSD.ORG>
Delivered-To: freebsd-arch@freebsd.org
Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34])
	by hub.freebsd.org (Postfix) with ESMTP id D0AE1106567D;
	Thu, 17 Apr 2008 13:44:56 +0000 (UTC) (envelope-from jhb@freebsd.org)
Received: from elvis.mu.org (elvis.mu.org [192.203.228.196])
	by mx1.freebsd.org (Postfix) with ESMTP id C2CB58FC27;
	Thu, 17 Apr 2008 13:44:56 +0000 (UTC) (envelope-from jhb@freebsd.org)
Received: from zion.baldwin.cx (unknown [208.65.89.154])
	by elvis.mu.org (Postfix) with ESMTP id 2E1AC1A4D8B;
	Thu, 17 Apr 2008 06:44:56 -0700 (PDT)
From: John Baldwin <jhb@freebsd.org>
To: Pawel Jakub Dawidek <pjd@freebsd.org>
Date: Thu, 17 Apr 2008 09:33:45 -0400
User-Agent: KMail/1.9.7
References: <20071218092222.GA9695@freebsd.org>
	<200804161014.41025.jhb@freebsd.org>
	<20080416165612.GA31094@garage.freebsd.pl>
In-Reply-To: <20080416165612.GA31094@garage.freebsd.pl>
MIME-Version: 1.0
Content-Type: text/plain;
  charset="iso-8859-15"
Content-Transfer-Encoding: 7bit
Content-Disposition: inline
Message-Id: <200804170933.45477.jhb@freebsd.org>
Cc: kib@freebsd.org, Roman Divacky <rdivacky@freebsd.org>, rwatson@freebsd.org,
	freebsd-arch@freebsd.org
Subject: Re: final decision about *at syscalls
X-BeenThere: freebsd-arch@freebsd.org
X-Mailman-Version: 2.1.5
Precedence: list
List-Id: Discussion related to FreeBSD architecture <freebsd-arch.freebsd.org>
List-Unsubscribe: <http://lists.freebsd.org/mailman/listinfo/freebsd-arch>,
	<mailto:freebsd-arch-request@freebsd.org?subject=unsubscribe>
List-Archive: <http://lists.freebsd.org/pipermail/freebsd-arch>
List-Post: <mailto:freebsd-arch@freebsd.org>
List-Help: <mailto:freebsd-arch-request@freebsd.org?subject=help>
List-Subscribe: <http://lists.freebsd.org/mailman/listinfo/freebsd-arch>,
	<mailto:freebsd-arch-request@freebsd.org?subject=subscribe>
X-List-Received-Date: Thu, 17 Apr 2008 13:44:56 -0000

On Wednesday 16 April 2008 12:56:12 pm Pawel Jakub Dawidek wrote:
> On Wed, Apr 16, 2008 at 10:14:40AM -0400, John Baldwin wrote:
> > On Saturday 12 April 2008 07:20:19 am Pawel Jakub Dawidek wrote:
> > > From what you write John, #1 is a better choice than #2. If you want to
> > > avoid races, you can pass already locked vnode. In case of file
> > > descriptors, if p_fd is not locked another thread can close and open
> > > different directory under the same descriptor number.
> >
> > Did you read Robert's paper?  Do you not realize that the kernel copying
> > data in from userland multiple times and having it change in between is
> > very bug prone?
>
> Believe me I'm fully aware of the problems Robert described in his
> paper. With vnode approach where do you have more data copying between
> kernel and userland?

Only because it was explicitly mentioned in the original e-mail:

> CONs of #1
> 
>         o       some very small code duplication (the translation is done in every 
>                 kern_fooat() function)
>         o       there is a race between the name translation and the actual use of the result
>                 of the translation that needs to be handled, the "path_to_file" string is copied
>                 to the kernel space twice hence a race

-- 
John Baldwin