From owner-freebsd-hackers@FreeBSD.ORG  Thu Oct 28 08:11:32 2010
Return-Path: <owner-freebsd-hackers@FreeBSD.ORG>
Delivered-To: freebsd-hackers@freebsd.org
Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34])
	by hub.freebsd.org (Postfix) with ESMTP id 955CF106564A;
	Thu, 28 Oct 2010 08:11:32 +0000 (UTC)
	(envelope-from perryh@pluto.rain.com)
Received: from agora.rdrop.com (agora.rdrop.com [IPv6:2607:f678:1010::34])
	by mx1.freebsd.org (Postfix) with ESMTP id 3BB0B8FC0A;
	Thu, 28 Oct 2010 08:11:32 +0000 (UTC)
Received: from agora.rdrop.com (66@localhost [127.0.0.1])
	by agora.rdrop.com (8.13.1/8.12.7) with ESMTP id o9S8BVFr069241
	(version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-SHA bits=256 verify=NOT);
	Thu, 28 Oct 2010 01:11:31 -0700 (PDT)
	(envelope-from perryh@pluto.rain.com)
Received: (from uucp@localhost)
	by agora.rdrop.com (8.13.1/8.12.9/Submit) with UUCP id o9S8BVKe069240; 
	Thu, 28 Oct 2010 01:11:31 -0700 (PDT)
Received: from fbsd61 by pluto.rain.com (4.1/SMI-4.1-pluto-M2060407)
	id AA13450; Thu, 28 Oct 10 01:02:13 PDT
Date: Thu, 28 Oct 2010 01:01:53 -0700
From: perryh@pluto.rain.com
To: ivoras@freebsd.org
Message-Id: <4cc92df1.Z0CRaJOCdvd/ZJSL%perryh@pluto.rain.com>
References: <20101026213618.GA3013@freebsd.org> <ia7nln$piv$1@dough.gmane.org>
	<4cc7ea44.ApOaxS8Xr4Sxu+0x%perryh@pluto.rain.com>
	<20101027111124.00007450@unknown> <ia8u9l$46j$1@dough.gmane.org>
In-Reply-To: <ia8u9l$46j$1@dough.gmane.org>
User-Agent: nail 11.25 7/29/05
Mime-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Transfer-Encoding: 7bit
Cc: freebsd-hackers@freebsd.org
Subject: Re: fsync(2) manual and hdd write caching
X-BeenThere: freebsd-hackers@freebsd.org
X-Mailman-Version: 2.1.5
Precedence: list
List-Id: Technical Discussions relating to FreeBSD
	<freebsd-hackers.freebsd.org>
List-Unsubscribe: <http://lists.freebsd.org/mailman/listinfo/freebsd-hackers>, 
	<mailto:freebsd-hackers-request@freebsd.org?subject=unsubscribe>
List-Archive: <http://lists.freebsd.org/pipermail/freebsd-hackers>
List-Post: <mailto:freebsd-hackers@freebsd.org>
List-Help: <mailto:freebsd-hackers-request@freebsd.org?subject=help>
List-Subscribe: <http://lists.freebsd.org/mailman/listinfo/freebsd-hackers>,
	<mailto:freebsd-hackers-request@freebsd.org?subject=subscribe>
X-List-Received-Date: Thu, 28 Oct 2010 08:11:32 -0000

Ivan Voras <ivoras@freebsd.org> wrote:

> ... The problem is actually pretty hard - since AFAIK SoftUpdates
> doesn't have "checkpoints" in the sense that it groups writes and
> all data "before" can guaranteed to be on-disk, the problem is
> *when* to issue BIO_FLUSH requests.

Seems to me the originally-stated problem -- making fsync(2)
do what it claims to do -- is not hard at all.  Just issue a
BIO_FLUSH request as the final step in handling fsync(2).

While we're at it, perhaps do the same in close(2).
I _hope_ we are already doing it in unmount(2).