Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755701Ab0GIKys (ORCPT ); Fri, 9 Jul 2010 06:54:48 -0400 Received: from smtp.ctxuk.citrix.com ([62.200.22.115]:58295 "EHLO SMTP.EU.CITRIX.COM" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753687Ab0GIKyr (ORCPT ); Fri, 9 Jul 2010 06:54:47 -0400 X-IronPort-AV: E=Sophos;i="4.53,563,1272844800"; d="scan'208";a="816299" Date: Fri, 9 Jul 2010 11:54:24 +0100 From: Stefano Stabellini X-X-Sender: sstabellini@kaball-desktop To: Ian Campbell CC: "ddutile@redhat.com" , Stefano Stabellini , "jeremy@goop.org" , "xen-devel@lists.xensource.com" , "stefano@stabellini.net" , "linux-kernel@vger.kernel.org" , "sheng@linux.intel.com" Subject: Re: [Xen-devel] Re: [PATCH 12/13] Unplug emulated disks and nics In-Reply-To: <1278662546.28432.602.camel@zakaz.uk.xensource.com> Message-ID: References: <1277136847-13266-12-git-send-email-stefano@stabellini.net> <4C2CEF56.4050008@redhat.com> <4C34DD1B.3010601@redhat.com> <4C362DC3.7000101@redhat.com> <1278624583.12109.15.camel@localhost.localdomain> <4C364A3F.8020900@redhat.com> <1278662546.28432.602.camel@zakaz.uk.xensource.com> User-Agent: Alpine 2.00 (DEB 1167 2008-08-23) MIME-Version: 1.0 Content-Type: text/plain; charset="US-ASCII" Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1905 Lines: 44 On Fri, 9 Jul 2010, Ian Campbell wrote: > > > > > Any guest which uses xvda in its configuration file today will be using > > > emulated devices but I think that with Stefano's patch and your proposed > > > change in default on a Xen system without support for unplug will start > > > using PV devices without unplugging the emulated ones first. > > > > > Well, Stefano requires the admin to add unplug switch to kernel cmd line, > > In the case where the host platform does not support the unplug protocol > this is correct and requiring explicit admin action to allow the PV > frontends to activate is the only safe option WRT the users data. > > However if the host platform does support the unplug protocol then this > is incorrect. In that case the default (in the absence of the command > line option) is to automatically unplug any device for which a PV driver > is available and so no command line option will be required in the > common case. (see xen_unplug_emulated_devices() under the comment "Set > the default value of xen_emul_unplug depending on...") > that's right: on host platforms supporting unplug no command line options are required; on the other hand if the host platform does not support unplug then xen_emul_unplug=ignore is required to use PV drivers anyway. > > so I don't see the harm in defaulting to unplug... > > As I described in my previous mail this is unsafe on host platforms > which do not support unplug. As I describe above it is unnecessary on > host platforms which do support unplug > yep, keep in mind the copy and paste example. If you are happy about the patch, I'll include it in my next version. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/