Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756457Ab0GINni (ORCPT ); Fri, 9 Jul 2010 09:43:38 -0400 Received: from mx1.redhat.com ([209.132.183.28]:44154 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755834Ab0GINnh (ORCPT ); Fri, 9 Jul 2010 09:43:37 -0400 Message-ID: <4C372743.6070003@redhat.com> Date: Fri, 09 Jul 2010 09:42:27 -0400 From: Don Dutile Reply-To: ddutile@redhat.com User-Agent: Thunderbird 2.0.0.18 (X11/20081113) MIME-Version: 1.0 To: Stefano Stabellini CC: Ian Campbell , "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 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> In-Reply-To: Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2398 Lines: 57 Stefano Stabellini wrote: > 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. > > I see by looking at xen_unplug_emulated_devices() closer, that the default unplugs emulated ide & emulated nic: if (xen_platform_pci_enabled && !xen_emul_unplug) I had to work around the fact that xen_platform_pci_enabled would not be set on rhel5-dom0 (no emul-unplug), so I hadn't looked at this default so closely. >>> 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. > Yes, the patch seems like a reasonable solution for running on older qemu-dm's. Thanks for the clarification(s). - Don -- 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/