From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([140.186.70.92]:52566) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1QqJfa-0004J7-Lx for qemu-devel@nongnu.org; Mon, 08 Aug 2011 02:50:39 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1QqJfZ-0002dN-Kh for qemu-devel@nongnu.org; Mon, 08 Aug 2011 02:50:38 -0400 Received: from e28smtp02.in.ibm.com ([122.248.162.2]:50393) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1QqJfY-0002d8-O2 for qemu-devel@nongnu.org; Mon, 08 Aug 2011 02:50:37 -0400 Received: from d28relay05.in.ibm.com (d28relay05.in.ibm.com [9.184.220.62]) by e28smtp02.in.ibm.com (8.14.4/8.13.1) with ESMTP id p786oV9o018739 for ; Mon, 8 Aug 2011 12:20:31 +0530 Received: from d28av05.in.ibm.com (d28av05.in.ibm.com [9.184.220.67]) by d28relay05.in.ibm.com (8.13.8/8.13.8/NCO v10.0) with ESMTP id p786oTOi1179872 for ; Mon, 8 Aug 2011 12:20:29 +0530 Received: from d28av05.in.ibm.com (loopback [127.0.0.1]) by d28av05.in.ibm.com (8.14.4/8.13.1/NCO v10.0 AVout) with ESMTP id p786oSjY016301 for ; Mon, 8 Aug 2011 16:50:29 +1000 Message-ID: <4E3F89FC.8090109@linux.vnet.ibm.com> Date: Mon, 08 Aug 2011 12:32:20 +0530 From: Supriya Kannery MIME-Version: 1.0 References: <4E3BB203.5060703@redhat.com> <20110805131247.GC6201@redhat.com> <20110805142812.GB17323@lst.de> <4E3C0FAA.2080303@redhat.com> <4E3C1117.8000009@codemonkey.ws> In-Reply-To: <4E3C1117.8000009@codemonkey.ws> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] Safely reopening image files by stashing fds Reply-To: supriyak@linux.vnet.ibm.com List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Anthony Liguori Cc: Kevin Wolf , Stefan Hajnoczi , qemu-devel , Christoph Hellwig , Paolo Bonzini On 08/05/2011 09:19 PM, Anthony Liguori wrote: > On 08/05/2011 10:43 AM, Kevin Wolf wrote: >> Am 05.08.2011 17:24, schrieb Stefan Hajnoczi: >>> On Fri, Aug 5, 2011 at 3:28 PM, Christoph Hellwig wrote: >>>> On Fri, Aug 05, 2011 at 02:12:48PM +0100, Daniel P. Berrange wrote: >>>>>> Because you cannot change O_DIRECT on an open fd :(. This is why >>>>>> we're going through this pain. >>>>> >>>>> Hmm, I remember hearing that before, but looking at the current >>>>> fcntl() >>>>> manpage, it claims you *can* change O_DIRECT using SET_FL. Perhaps >>>>> this >>>>> is a newish feature, but it'd be nicer to use it if possible ? >>>> >>>> It's been there since day 1 of O_DIRECT support. >>> >>> Sorry, my bad. So for Linux we could just use fcntl for >>> block_set_hostcache and not bother with reopening. However, we will >>> need to reopen should we wish to support changing O_DSYNC. >> >> We do wish to support that. >> >> Anthony thinks that allowing the guest to toggle WCE is a prerequisite >> for making cache=writeback the default. And this is something that I >> definitely want to do for 1.0. > > Indeed. > We discussed the following so far... 1. How to safely reopen image files 2. Dynamic hostcache change 3. Support for dynamic change of O_DSYNC Since 2 is independent of 1, shall I go ahead implementing hostcache change using fcntl. Implementation for safely reopening image files using "BDRVReopenState" can be done separately as a pre-requisite before implementing 3 Thanks, Supriya > Regards, > > Anthony Liguori > >> Kevin >> > >