From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([140.186.70.92]:50260) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1QDA0w-0006J4-Ku for qemu-devel@nongnu.org; Fri, 22 Apr 2011 02:38:51 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1QDA0v-0000W3-QL for qemu-devel@nongnu.org; Fri, 22 Apr 2011 02:38:50 -0400 Received: from verein.lst.de ([213.95.11.211]:34105 helo=newverein.lst.de) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1QDA0v-0000Vw-Hn for qemu-devel@nongnu.org; Fri, 22 Apr 2011 02:38:49 -0400 Date: Fri, 22 Apr 2011 08:38:48 +0200 From: Christoph Hellwig Message-ID: <20110422063848.GA11449@lst.de> References: <4db09239.0b968e0a.4145.ffffada2@mx.google.com> <20110422040852.GA9493@lst.de> <20110422061347.GA11066@lst.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Subject: Re: [Qemu-devel] iSCSI support for QEMU, update List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: ronnie sahlberg Cc: kwolf@redhat.com, Christoph Hellwig , stefanha@linux.vnet.ibm.com, qemu-devel@nongnu.org On Fri, Apr 22, 2011 at 04:35:11PM +1000, ronnie sahlberg wrote: > Ok, I am confused And this time it's my fault, sorry. > I have to set FUA if the WB(I guessed this meant write-back) flag is set? > Not the opposite (I assume opposite of write-back is write-through) ? Sorry, I meant exactly the opposite. You do not have to set FUA if either of those two flags is present, so: if (flags & (BDRV_O_CACHE_WB|BDRV_O_NOCACHE)) caching is ok, write with FUA=0 else caching is NOT ok, write with FUA=1