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[82.29.237.198]) by smtp.gmail.com with ESMTPSA id r67sm6187364wma.6.2021.07.14.11.39.48 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 14 Jul 2021 11:39:49 -0700 (PDT) Date: Wed, 14 Jul 2021 19:39:46 +0100 From: "Dr. David Alan Gilbert" To: Kunkun Jiang Subject: Re: [PATCH 1/2] qapi/run-state: Add a new shutdown cause 'migration-completed' Message-ID: References: <20210705123653.1315-1-jiangkunkun@huawei.com> <20210705123653.1315-2-jiangkunkun@huawei.com> <7b8324e9-85d8-1b14-4e63-308ea2563d56@huawei.com> MIME-Version: 1.0 In-Reply-To: User-Agent: Mutt/2.0.7 (2021-05-04) Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=dgilbert@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit Received-SPF: pass client-ip=170.10.133.124; envelope-from=dgilbert@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -34 X-Spam_score: -3.5 X-Spam_bar: --- X-Spam_report: (-3.5 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.699, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H4=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Daniel =?iso-8859-1?Q?P=2E_Berrang=E9?= , Juan Quintela , "open list:All patches CC here" , Markus Armbruster , wanghaibin.wang@huawei.com, Paolo Bonzini , Eric Blake Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" * Kunkun Jiang (jiangkunkun@huawei.com) wrote: > On 2021/7/6 18:27, Dr. David Alan Gilbert wrote: > > * Kunkun Jiang (jiangkunkun@huawei.com) wrote: > > > Hi Daniel, > > > > > > On 2021/7/5 20:48, Daniel P. Berrangé wrote: > > > > On Mon, Jul 05, 2021 at 08:36:52PM +0800, Kunkun Jiang wrote: > > > > > In the current version, the source QEMU process does not automatic > > > > > exit after a successful migration. Additional action is required, > > > > > such as sending { "execute": "quit" } or ctrl+c. For simplify, add > > > > > a new shutdown cause 'migration-completed' to exit the source QEMU > > > > > process after a successful migration. > > > > IIUC, 'STATUS_COMPLETED' state is entered on the source host > > > > once it has finished sending all VM state, and thus does not > > > > guarantee that the target host has successfully received and > > > > loaded all VM state. > > > Thanks for your reply. > > > > > > If the target host doesn't successfully receive and load all VM state, > > > we can send { "execute": "cont" } to resume the soruce in time to > > > ensure that VM will not lost? > > Yes, that's pretty common at the moment; the failed migration can > > happen at lots of different points: > > a) The last part of the actual migration stream/loading the devices > > - that's pretty easy, since the destination hasn't actually got > > the full migration stream. > > > > b) If the migration itself completes, but then the management system > > then tries to reconfigure the networking/storage on the destination, > > and something goes wrong in that, then it can roll that back and > > cont on the source. > > > > So, it's a pretty common type of failure/recovery - the management > > application has to be a bit careful not to do anything destructive > > until as late as possible, so it knows it can switch back. > Okay， I see. > > > > Typically a mgmt app will need to directly confirm that the > > > > target host QEMU has succesfully started running, before it > > > > will tell the source QEMU to quit. > > > 'a mgmt app', such as libvirt? > > Yes, it's currently libvirt that does that; but any of the control > > things could (it's just libvirt has been going long enough so it knows > > about lots and lots of nasty cases of migration failure, and recovering > > properly). > > > > Can you explain why did you want to get the source to automatically > > quit? In a real setup where does it help? > Sorry, my thoughts on live migration scenarios are not comprehensive enough. That's OK; it takes a little while to understand all of the recovery and error cases; people *really* want to recover from a failed migration; so we try and be very careful about not throwing away the source. Dave > Thanks, > Kunkun Jiang > > Dave > > > > > > > Thanks, > > > Kunkun Jiang > > > > So, AFAICT, this automatic exit after STATUS_COMPLETED is > > > > not safe and could lead to total loss of the running VM in > > > > error scenarios. > > > > > > > > > > > > > > > > > Signed-off-by: Kunkun Jiang > > > > > --- > > > > > migration/migration.c | 1 + > > > > > qapi/run-state.json | 4 +++- > > > > > 2 files changed, 4 insertions(+), 1 deletion(-) > > > > > > > > > > diff --git a/migration/migration.c b/migration/migration.c > > > > > index 4228635d18..16782c93c2 100644 > > > > > --- a/migration/migration.c > > > > > +++ b/migration/migration.c > > > > > @@ -3539,6 +3539,7 @@ static void migration_iteration_finish(MigrationState *s) > > > > > case MIGRATION_STATUS_COMPLETED: > > > > > migration_calculate_complete(s); > > > > > runstate_set(RUN_STATE_POSTMIGRATE); > > > > > + qemu_system_shutdown_request(SHUTDOWN_CAUSE_MIGRATION_COMPLETED); > > > > > break; > > > > > case MIGRATION_STATUS_ACTIVE: > > > > > diff --git a/qapi/run-state.json b/qapi/run-state.json > > > > > index 43d66d700f..66aaef4e2b 100644 > > > > > --- a/qapi/run-state.json > > > > > +++ b/qapi/run-state.json > > > > > @@ -86,12 +86,14 @@ > > > > > # ignores --no-reboot. This is useful for sanitizing > > > > > # hypercalls on s390 that are used during kexec/kdump/boot > > > > > # > > > > > +# @migration-completed: Reaction to the successful migration > > > > > +# > > > > > ## > > > > > { 'enum': 'ShutdownCause', > > > > > # Beware, shutdown_caused_by_guest() depends on enumeration order > > > > > 'data': [ 'none', 'host-error', 'host-qmp-quit', 'host-qmp-system-reset', > > > > > 'host-signal', 'host-ui', 'guest-shutdown', 'guest-reset', > > > > > - 'guest-panic', 'subsystem-reset'] } > > > > > + 'guest-panic', 'subsystem-reset', 'migration-completed'] } > > > > > ## > > > > > # @StatusInfo: > > > > > -- > > > > > 2.23.0 > > > > > > > > > > > > > > Regards, > > > > Daniel > > > > -- Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK