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[99.254.114.190]) by smtp.gmail.com with ESMTPSA id 586e51a60fabf-29487429433sm3044133fac.6.2024.11.04.09.18.23 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 04 Nov 2024 09:18:24 -0800 (PST) Date: Mon, 4 Nov 2024 12:18:22 -0500 From: Peter Xu To: Prasad Pandit Cc: qemu-devel@nongnu.org, Fabiano Rosas , Prasad Pandit Subject: Re: [PATCH 2/5] migration/postcopy: magic value for postcopy channel Message-ID: References: <20241029150908.1136894-1-ppandit@redhat.com> <20241029150908.1136894-3-ppandit@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: Received-SPF: pass client-ip=170.10.129.124; envelope-from=peterx@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -23 X-Spam_score: -2.4 X-Spam_bar: -- X-Spam_report: (-2.4 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.34, 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, RCVD_IN_VALIDITY_CERTIFIED_BLOCKED=0.001, RCVD_IN_VALIDITY_RPBL_BLOCKED=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: 2.1.29 Precedence: list List-Id: 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 Mon, Nov 04, 2024 at 06:02:33PM +0530, Prasad Pandit wrote: > On Fri, 1 Nov 2024 at 20:04, Peter Xu wrote: > > As we discussed internally, we can't do this unconditionally. We at least > > some compat properties. > > * ie. we define a new compat property to check if postcopy sends a > magic value or not? > > > Or we need to see whether Fabiano's handshake can > > simplify this, because the handshake will also re-design the channel > > establishment protocol. > > * May I know more about this handshake change? Is there a repository? > OR a page/document that describes what is being planned? Is it just > channel establishment change or there's more to it? After a 2nd thought, maybe we don't need a new compat property, and this should work even before handshake ready. Firstly, we'll need a way to tell mgmt that the new qemu binary supports enablement of both multifd + postcopy feature. That can be done with a "features": [ "postcopy-with-multifd-precopy" ] Flag attached to the QMP "migrate" command. Then, I think we don't need a magic for preempt channel, because new qemu binaries (after 7.2) have no issue on out-of-order connections between main / preempt channel. Preempt channel is always connected later than main. It means in the test logic of "which channel is which", it should be: - If it's a multifd channel (check multifd header match), it's a multifd channel, otherwise, - if main channel is not present yet, it must be the main channel (and we can double check the main channel magic), otherwise, - it's the preempt channel With that, I think we can drop the new magic sent here. Thanks, -- Peter Xu