From mboxrd@z Thu Jan 1 00:00:00 1970 From: Konrad Rzeszutek Wilk Subject: Re: blkif discard attributes Date: Mon, 7 Jul 2014 14:40:58 -0400 Message-ID: <20140707184058.GC30717@laptop.dumpdata.com> References: <53B5298D020000780001FF48@mail.emea.novell.com> <53B525B4.7080606@citrix.com> <53B547BC0200007800020148@mail.emea.novell.com> <53B52DB9.9000301@citrix.com> <53B54B7E02000078000201AC@mail.emea.novell.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Received: from mail6.bemta4.messagelabs.com ([85.158.143.247]) by lists.xen.org with esmtp (Exim 4.72) (envelope-from ) id 1X4Dqd-0000Ng-Nr for xen-devel@lists.xenproject.org; Mon, 07 Jul 2014 18:41:08 +0000 Content-Disposition: inline In-Reply-To: <53B54B7E02000078000201AC@mail.emea.novell.com> List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xen.org Errors-To: xen-devel-bounces@lists.xen.org To: Jan Beulich Cc: xen-devel , Boris Ostrovsky , David Vrabel List-Id: xen-devel@lists.xenproject.org On Thu, Jul 03, 2014 at 11:24:30AM +0100, Jan Beulich wrote: > >>> On 03.07.14 at 12:17, wrote: > > On 03/07/14 11:08, Jan Beulich wrote: > >>>>> On 03.07.14 at 11:43, wrote: > >>> On 03/07/14 08:59, Jan Beulich wrote: > >>>> discard_zeroes_data also be communicated from backend to frontend? > >>> > >>> Perhaps. But how would you handle a guest that used to have > >>> discard_zeroes_data but is restored with different storage that no > >>> longer has this property? > >> > >> Don't these attributes gets re-evaluated after restore anyway? > > > > I don't see how that helps. What if a discard request was submitted > > before the suspend, expecting the discard to zero and on restore the > > requests is queued for the new backend which then might not zero. > > Hmm, good point. So it's then indeed better to not communicate this. > Albeit similar issues arise with the existing attributes we communicate: > What if the new backend doesn't satisfy the assumptions on the old > one? Possibly the request may get failed, but possibly it may also get > executed wrongly. Neither of which is very desirable. That is OK with discard operations. It is OK if they fail intermediately. > > Jan >