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Wed, 21 Jan 2026 14:22:43 -0800 (PST) Date: Wed, 21 Jan 2026 17:22:41 -0500 From: Peter Xu To: "Dr. David Alan Gilbert" Cc: Lukas Straub , qemu-devel@nongnu.org, Juraj Marcin , Fabiano Rosas , Markus Armbruster , Daniel P =?utf-8?B?LiBCZXJyYW5nw6k=?= , =?utf-8?B?THVrw6HFoQ==?= Doktor , Juan Quintela , Zhang Chen , zhanghailiang@xfusion.com, Li Zhijian , Jason Wang Subject: Re: [PATCH 1/3] migration/colo: Deprecate COLO migration framework Message-ID: References: <20260120110811.7df19a6c@penguin> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: Received-SPF: pass client-ip=170.10.133.124; envelope-from=peterx@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -21 X-Spam_score: -2.2 X-Spam_bar: -- X-Spam_report: (-2.2 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.069, 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_H3=0.001, RCVD_IN_MSPIKE_WL=0.001, RCVD_IN_VALIDITY_CERTIFIED_BLOCKED=0.001, RCVD_IN_VALIDITY_RPBL_BLOCKED=0.001, SPF_HELO_PASS=-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: 2.1.29 Precedence: list List-Id: qemu development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org On Wed, Jan 21, 2026 at 09:31:29PM +0000, Dr. David Alan Gilbert wrote: > * Peter Xu (peterx@redhat.com) wrote: > > On Wed, Jan 21, 2026 at 05:31:32PM +0000, Dr. David Alan Gilbert wrote: > > > Right that's true for postcopy; but then the only way to load the stream into > > > that buffer is to load it all at once because of the vmstate problem above. > > > (and because in the original postcopy we needed the original fd free > > > for page requests; you might be able to avoid that with multifd now) > > > > Only until now, I recognized that COLO wants to make sure the checkpoint is > > either completely applied or none applied. > > > > So the specialty is COLO does loadvm on top of a running VM, meanwhile COLO > > may decide to not loadvm afterwards if checkpoint wasn't correctly > > received. > > Oh yes; because if your secondary is running happily, your primary could > fail while it was sending you a new snapshot - and then the secondary > has to be able to carry on. > > > And yes, to cache all device states with current section header definition > > in the stream, we'll likely need a size. We can still parse the stream as > > you pointed out previously, but I agree a special SIZE header still makes > > sense. > > Well, *can't* parse the stream as I said; because of the get()/put() stuff > without rewriting that. Ah, yes.. -- Peter Xu