From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mailman by lists.gnu.org with tmda-scanned (Exim 4.43) id 1M1TRp-00068M-0P for qemu-devel@nongnu.org; Tue, 05 May 2009 18:49:13 -0400 Received: from exim by lists.gnu.org with spam-scanned (Exim 4.43) id 1M1TRj-00066e-IQ for qemu-devel@nongnu.org; Tue, 05 May 2009 18:49:11 -0400 Received: from [199.232.76.173] (port=53650 helo=monty-python.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1M1TRj-00066a-DK for qemu-devel@nongnu.org; Tue, 05 May 2009 18:49:07 -0400 Received: from mail2.shareable.org ([80.68.89.115]:56851) by monty-python.gnu.org with esmtps (TLS-1.0:RSA_AES_256_CBC_SHA1:32) (Exim 4.60) (envelope-from ) id 1M1TRj-0006SP-3S for qemu-devel@nongnu.org; Tue, 05 May 2009 18:49:07 -0400 Date: Tue, 5 May 2009 23:49:04 +0100 From: Jamie Lokier Subject: Re: [Qemu-devel] barriers: block layer preparations Message-ID: <20090505224904.GI7574@shareable.org> References: <20090505120804.GA30651@lst.de> <20090505120817.GA30721@lst.de> <4A00446B.7070404@redhat.com> <20090505205716.GA24320@lst.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20090505205716.GA24320@lst.de> List-Id: qemu-devel.nongnu.org List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Christoph Hellwig Cc: Avi Kivity , qemu-devel@nongnu.org Christoph Hellwig wrote: > > A barrier for read can be meaningful if the guest wishes to read a > > known-to-be-stable write. I don't think any guest can make use of this > > though. > > I don't know of any storage standard having anything like this or any > OS taking advantage of it. I'd be happy to review anything like that, > though. Several OSes have O_RSYNC, meaning reads hit the storage instead of the OS cache. I don't know if they bypass storage caches, but the purpose seems to be to verify writes, and they will certainly bypass storage caches if the OS or user turns off the storage caches. -- Jamie