From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.5 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,T_HK_NAME_DR,USER_AGENT_MUTT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 7C6ABC04AB4 for ; Tue, 14 May 2019 15:19:21 +0000 (UTC) Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1 with cipher AES256-SHA (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 4FFFD2085A for ; Tue, 14 May 2019 15:19:21 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 4FFFD2085A Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([127.0.0.1]:49746 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1hQZD6-0008Pt-BT for qemu-devel@archiver.kernel.org; Tue, 14 May 2019 11:19:20 -0400 Received: from eggs.gnu.org ([209.51.188.92]:52171) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1hQZC7-000865-Gm for qemu-devel@nongnu.org; Tue, 14 May 2019 11:18:20 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1hQZC6-0007CK-Ij for qemu-devel@nongnu.org; Tue, 14 May 2019 11:18:19 -0400 Received: from mx1.redhat.com ([209.132.183.28]:37672) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1hQZC6-0007Aw-DM for qemu-devel@nongnu.org; Tue, 14 May 2019 11:18:18 -0400 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.phx2.redhat.com [10.5.11.13]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id B1D0381F0C; Tue, 14 May 2019 15:18:17 +0000 (UTC) Received: from work-vm (ovpn-117-232.ams2.redhat.com [10.36.117.232]) by smtp.corp.redhat.com (Postfix) with ESMTPS id B22B7608AB; Tue, 14 May 2019 15:18:16 +0000 (UTC) Date: Tue, 14 May 2019 16:18:14 +0100 From: "Dr. David Alan Gilbert" To: Wei Yang Message-ID: <20190514151813.GL2753@work-vm> References: <20190424004700.12766-1-richardw.yang@linux.intel.com> <20190424004700.12766-3-richardw.yang@linux.intel.com> <0eb5e5a5-593e-f4a2-7e2d-a9fed481ab6c@gmail.com> <20190426005133.GB25513@richard> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline In-Reply-To: <20190426005133.GB25513@richard> User-Agent: Mutt/1.11.4 (2019-03-13) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.27]); Tue, 14 May 2019 15:18:17 +0000 (UTC) Content-Transfer-Encoding: quoted-printable X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] X-Received-From: 209.132.183.28 Subject: Re: [Qemu-devel] [PATCH 2/4] migration/savevm: use migration_is_blocked to validate X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.21 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Daniel Henrique Barboza , qemu-devel@nongnu.org, quintela@redhat.com Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" * Wei Yang (richardw.yang@linux.intel.com) wrote: > On Thu, Apr 25, 2019 at 05:55:15PM -0300, Daniel Henrique Barboza wrote= : > > > > > >On 4/23/19 9:46 PM, Wei Yang wrote: > >> migration_is_blocked() is used in migrate_prepare() and > >> save_snapshot(), this is more proper to use this instead of > >> qemu_savevm_state_blocked() in qemu_loadvm_state(). > > > > > >migration_is_blocked() does an additional verification: > > > >"if (migration_blockers)" > > > >comparing to what was previously done in qemu_loadvm_state. > > > >I've checked what migration_blockers does and it is a GList used > >for callers to block the migration process. This is used via > >'migration_add_blocker', from migration.c. > > > >'migration_add_blocker' is called all over the place, most notably > >in=A0 _realize() functions=A0 and _open() functions from block. > > > >Thus, I am not sure if this change will impact the use of > >qemu_loadvm_state() from load_snapshot() (i.e. can load_snapshot > >be called with migration_blockers?). It's better to someone > >with a better understanding of this code to comment on that. > > >=20 > Well, when you look into the source side of migration: >=20 > qmp_migrate > migrate_prepare > migration_is_blocked >=20 > This means if migration_is_blocked fails, the source will not start mig= ration. > And it is the same as save_snapshot. >=20 > From my understanding, when we load a vm, it should check the same > requirement. I've been thinking about this, and I think I agree with Daniel on this. The 'migration_blockers' list tells you that something about the *current* state of a device means that it can't be migrated - e.g. a 9pfs with a mounted filesystem can't be migrated. If we're about to reload the state from a snapshot, then the saved snapshot's state must have been migratable, so that's OK. (Whether all the device code is actually OK about being reset in that state is a different question; but I think it should be). Dave > --=20 > Wei Yang > Help you, Help me -- Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK