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Wed, 2 Sep 2020 07:55:18 +0000 (UTC) Received: by blackfin.pond.sub.org (Postfix, from userid 1000) id 6BAB0113C418; Wed, 2 Sep 2020 09:55:17 +0200 (CEST) From: Markus Armbruster To: Daniel P. =?utf-8?Q?Berrang=C3=A9?= Subject: Re: [PATCH v8 1/8] Introduce yank feature References: <874kohsgsp.fsf@dusky.pond.sub.org> <20200901152259.GO345480@redhat.com> Date: Wed, 02 Sep 2020 09:55:17 +0200 In-Reply-To: <20200901152259.GO345480@redhat.com> ("Daniel P. =?utf-8?Q?Be?= =?utf-8?Q?rrang=C3=A9=22's?= message of "Tue, 1 Sep 2020 16:22:59 +0100") Message-ID: <87a6y8oboa.fsf@dusky.pond.sub.org> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/27.1 (gnu/linux) MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.84 on 10.5.11.23 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=armbru@redhat.com X-Mimecast-Spam-Score: 0.002 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable Received-SPF: pass client-ip=205.139.110.120; envelope-from=armbru@redhat.com; helo=us-smtp-1.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/09/02 02:26:30 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H2=-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: Kevin Wolf , Lukas Straub , qemu-block , Juan Quintela , qemu-devel , Max Reitz , =?utf-8?Q?Marc-Andr=C3=A9?= Lureau , Paolo Bonzini , "Dr. David Alan Gilbert" Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" Daniel P. Berrang=C3=A9 writes: > On Tue, Sep 01, 2020 at 04:38:46PM +0200, Markus Armbruster wrote: >> One more question... >>=20 >> Lukas Straub writes: >>=20 >> > The yank feature allows to recover from hanging qemu by "yanking" >> > at various parts. Other qemu systems can register themselves and >> > multiple yank functions. Then all yank functions for selected >> > instances can be called by the 'yank' out-of-band qmp command. >> > Available instances can be queried by a 'query-yank' oob command. >> > >> > Signed-off-by: Lukas Straub >> > Acked-by: Stefan Hajnoczi >> [...] >> > diff --git a/qapi/misc.json b/qapi/misc.json >> > index 9d32820dc1..7de330416a 100644 >> > --- a/qapi/misc.json >> > +++ b/qapi/misc.json >> > @@ -1615,3 +1615,65 @@ >> > ## >> > { 'command': 'query-vm-generation-id', 'returns': 'GuidInfo' } >> > >> > +## >> > +# @YankInstances: >> > +# >> > +# @instances: List of yank instances. >> > +# >> > +# A yank instance can be yanked with the "yank" qmp command to recove= r from a >> > +# hanging qemu. >> > +# >> > +# Yank instances are named after the following schema: >> > +# "blockdev:" refers to a block device. Currently only nbd= block >> > +# devices are implemented. >> > +# "chardev:" refers to a chardev. Currently only socket= chardevs >> > +# are implemented. >> > +# "migration" refers to the migration currently in progress. >> > +# >> > +# Currently implemented yank instances: >> > +# -nbd block device: >> > +# Yanking it will shutdown the connection to the nbd server without >> > +# attempting to reconnect. >> > +# -socket chardev: >> > +# Yanking it will shutdown the connected socket. >> > +# -migration: >> > +# Yanking it will shutdown all migration connections. >>=20 >> How is yanking migration related to command migrate_cancel? > > migrate_cancel will do a shutdown() on the primary migration socket only. > In addition it will toggle the migration state. > > Yanking will do a shutdown on all migration sockets (important for > multifd), but won't touch migration state or any other aspect of QEMU > code. > > Overall yanking has less potential for things to go wrong than the > migrate_cancel method, as it doesn't try to do any kind of cleanup > or migration. Thanks. Would it make sense to work this into the documentation?