From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:34268) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1UzUa8-0005mR-TR for qemu-devel@nongnu.org; Wed, 17 Jul 2013 12:28:01 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1UzUa8-0002qB-3Y for qemu-devel@nongnu.org; Wed, 17 Jul 2013 12:28:00 -0400 Received: from mx1.redhat.com ([209.132.183.28]:53087) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1UzUa7-0002og-SR for qemu-devel@nongnu.org; Wed, 17 Jul 2013 12:28:00 -0400 Message-ID: <51E6C5FC.1030304@redhat.com> Date: Wed, 17 Jul 2013 18:27:40 +0200 From: Paolo Bonzini MIME-Version: 1.0 References: <1373885375-13601-1-git-send-email-pl@kamp.de> <1373885375-13601-5-git-send-email-pl@kamp.de> <20130717084648.GD2458@dhcp-200-207.str.redhat.com> <51E66ACD.70706@redhat.com> <20130717102551.GF2458@dhcp-200-207.str.redhat.com> In-Reply-To: Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [PATCH 4/4] qemu-img: conditionally discard target on convert List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: ronnie sahlberg Cc: Kevin Wolf , Peter Lieven , qemu-devel , Stefan Hajnoczi Il 17/07/2013 17:54, ronnie sahlberg ha scritto: > I think it is reasonable to assume that IF LBPRZ==1 and IF it is an > "optimal unmap request" then the blocks will become unmapped and they > will read back as 0. Yes, but it is not reasonable to assume that bdrv_discard will only receive "optimal" requests. Thus, using WRITE SAME for LBPRZ=1, and not exposing LBPRZ=1 if LBPWS=0 (may also use LBPWS10 depending on the capacity), is the safer thing to do. Paolo