From mboxrd@z Thu Jan  1 00:00:00 1970
Received: from eggs.gnu.org ([208.118.235.92]:34297)
	by lists.gnu.org with esmtp (Exim 4.71)
	(envelope-from <pbonzini@redhat.com>) id 1SlLT0-00010r-LI
	for qemu-devel@nongnu.org; Sun, 01 Jul 2012 10:49:39 -0400
Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71)
	(envelope-from <pbonzini@redhat.com>) id 1SlLSz-0006go-1s
	for qemu-devel@nongnu.org; Sun, 01 Jul 2012 10:49:38 -0400
Received: from mx1.redhat.com ([209.132.183.28]:4881)
	by eggs.gnu.org with esmtp (Exim 4.71)
	(envelope-from <pbonzini@redhat.com>) id 1SlLSy-0006gd-Pp
	for qemu-devel@nongnu.org; Sun, 01 Jul 2012 10:49:36 -0400
Message-ID: <4FF06379.9030808@redhat.com>
Date: Sun, 01 Jul 2012 16:49:29 +0200
From: Paolo Bonzini <pbonzini@redhat.com>
MIME-Version: 1.0
References: <20120611141806.GA2737@in.ibm.com>
	<20120611142144.GD2737@in.ibm.com>
	<CAJSP0QXRdEtzqeWYSv6gzgwkP1LT+TDDUEEMpbiB1P9EbLvFAQ@mail.gmail.com>
In-Reply-To: <CAJSP0QXRdEtzqeWYSv6gzgwkP1LT+TDDUEEMpbiB1P9EbLvFAQ@mail.gmail.com>
Content-Type: text/plain; charset=ISO-8859-1
Content-Transfer-Encoding: 7bit
Subject: Re: [Qemu-devel] [RFC PATCH 3/3] block: gluster as block backend
List-Id: <qemu-devel.nongnu.org>
List-Unsubscribe: <https://lists.nongnu.org/mailman/options/qemu-devel>,
	<mailto:qemu-devel-request@nongnu.org?subject=unsubscribe>
List-Archive: <http://lists.nongnu.org/archive/html/qemu-devel>
List-Post: <mailto:qemu-devel@nongnu.org>
List-Help: <mailto:qemu-devel-request@nongnu.org?subject=help>
List-Subscribe: <https://lists.nongnu.org/mailman/listinfo/qemu-devel>,
	<mailto:qemu-devel-request@nongnu.org?subject=subscribe>
To: Stefan Hajnoczi <stefanha@gmail.com>
Cc: Kevin Wolf <kwolf@redhat.com>, Vijay Bellur <vbellur@redhat.com>, Amar Tumballi <amarts@redhat.com>, qemu-devel@nongnu.org, bharata@linux.vnet.ibm.com

Il 18/06/2012 19:35, Stefan Hajnoczi ha scritto:
>> > +    /* Use O_DSYNC for write-through caching, no flags for write-back caching,
>> > +     * and O_DIRECT for no caching. */
>> > +    if ((bdrv_flags & BDRV_O_NOCACHE))
>> > +        s->open_flags |= O_DIRECT;
>> > +    if (!(bdrv_flags & BDRV_O_CACHE_WB))
>> > +        s->open_flags |= O_DSYNC;
> Paolo has changed this recently, you might need to use
> bs->enable_write_cache instead.

At the protocol (i.e. low-level backend) level you don't need to do
anything really, if you implement bdrv_flush_to_disk correctly.

Looking at BDRV_O_CACHE_WB will do no harm, it's just dead code.

Paolo