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Wed, 5 Aug 2020 10:47:25 +0000 (UTC) Date: Wed, 5 Aug 2020 11:47:23 +0100 From: "Dr. David Alan Gilbert" To: Peter Maydell Subject: Re: [PATCH 02/18] migration/vmstate: Introduce vmstate_no_state_to_migrate Message-ID: <20200805104723.GC3004@work-vm> References: <20200703201911.26573-1-f4bug@amsat.org> <20200703201911.26573-3-f4bug@amsat.org> MIME-Version: 1.0 In-Reply-To: User-Agent: Mutt/1.14.6 (2020-07-11) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 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=iso-8859-1 Content-Transfer-Encoding: 8bit Content-Disposition: inline Received-SPF: pass client-ip=205.139.110.61; envelope-from=dgilbert@redhat.com; helo=us-smtp-delivery-1.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/08/05 04:10:11 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] X-Spam_score_int: -40 X-Spam_score: -4.1 X-Spam_bar: ---- X-Spam_report: (-4.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-1, 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=-1, 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: Laurent Vivier , Gerd Hoffmann , Daniel =?iso-8859-1?Q?P=2E_Berrang=E9?= , Eduardo Habkost , Juan Quintela , Andrew Jeffery , Mark Cave-Ayland , Philippe =?iso-8859-1?Q?Mathieu-Daud=E9?= , Andrew Baumann , QEMU Developers , qemu-arm , =?iso-8859-1?Q?C=E9dric?= Le Goater , Paolo Bonzini , Subbaraya Sundeep , Philippe =?iso-8859-1?Q?Mathieu-Daud=E9?= , Artyom Tarasenko , Joel Stanley Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" * Peter Maydell (peter.maydell@linaro.org) wrote: > On Fri, 3 Jul 2020 at 21:19, Philippe Mathieu-Daudé wrote: > > > > Introduce a special state to indicate when an object doesn't > > have anything in its state to migrate. > > > > Suggested-by: Peter Maydell > > Signed-off-by: Philippe Mathieu-Daudé > > --- > > include/migration/vmstate.h | 1 + > > migration/vmstate.c | 7 +++++++ > > 2 files changed, 8 insertions(+) > > > > diff --git a/include/migration/vmstate.h b/include/migration/vmstate.h > > index af7d80cd4e..0922bc8efa 100644 > > --- a/include/migration/vmstate.h > > +++ b/include/migration/vmstate.h > > @@ -195,6 +195,7 @@ struct VMStateDescription { > > }; > > > > extern const VMStateDescription vmstate_dummy; /* Exclusively for linux-user */ > > +extern const VMStateDescription vmstate_no_state_to_migrate; > > > > extern const VMStateInfo vmstate_info_bool; > > > > diff --git a/migration/vmstate.c b/migration/vmstate.c > > index bafa890384..d640cafad3 100644 > > --- a/migration/vmstate.c > > +++ b/migration/vmstate.c > > @@ -20,6 +20,13 @@ > > #include "trace.h" > > #include "qjson.h" > > > > +const VMStateDescription vmstate_no_state_to_migrate = { > > + .name = "empty-state", > > + .fields = (VMStateField[]) { > > + VMSTATE_END_OF_LIST() > > + } > > +}; > > Does this definitely not put any data into the migration stream? > We don't want to change what's on the wire for machines that > use devices that start using this. (If it does by default, it > would be easy to make the migration code special case the > magic symbol to act like "no vmsd specified"). I'd need to test it to be sure, but I think if we added a .needed to vmstate_no_state_to_migrate with a function that always returned false, then I think the stream would stay unchanged. Dave > thanks > -- PMM > -- Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK