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[99.254.114.190]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-20c138b047fsm74322475ad.44.2024.10.09.12.06.55 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 09 Oct 2024 12:06:57 -0700 (PDT) Date: Wed, 9 Oct 2024 15:06:53 -0400 From: Peter Xu To: Steven Sistare Cc: Fabiano Rosas , qemu-devel@nongnu.org, David Hildenbrand , Marcel Apfelbaum , Eduardo Habkost , Philippe Mathieu-Daude , Paolo Bonzini , "Daniel P. Berrange" , Markus Armbruster Subject: Re: [PATCH V2 13/13] migration: cpr-transfer mode Message-ID: References: <1727725244-105198-1-git-send-email-steven.sistare@oracle.com> <1727725244-105198-14-git-send-email-steven.sistare@oracle.com> <87ed4qtpo1.fsf@suse.de> <877caitno5.fsf@suse.de> <8b92a6ee-19f7-4483-9766-6b849cc04017@oracle.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <8b92a6ee-19f7-4483-9766-6b849cc04017@oracle.com> 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=-0.151, 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_RPBL_BLOCKED=0.001, RCVD_IN_VALIDITY_SAFE_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 Wed, Oct 09, 2024 at 02:43:44PM -0400, Steven Sistare wrote: > On 10/8/2024 3:48 PM, Peter Xu wrote: > > On Tue, Oct 08, 2024 at 04:11:38PM -0300, Fabiano Rosas wrote: > > > As of half an hour ago =) We could put a feature branch up and work > > > together, if you have more concrete thoughts on how this would look like > > > let me know. > > > > [I'll hijack this thread with one more email, as this is not cpr-relevant] > > > > I think I listed all the things I can think of in the wiki, so please go > > ahead. > > > > One trivial suggestion is we can start from the very simple, which is the > > handshake itself, with a self-bootstrap protocol, probably feature-bit > > based or whatever you prefer. Then we set bit 0 saying "this QEMU knows > > how to handshake". > > > > Comparing to the rest requirement, IMHO we can make the channel > > establishment the 1st feature, then it's already good for merging, having > > feature bit 1 saying "this qemu understands named channel establishment". > > > > Then we add new feature bits on top of the handshake feature, by adding > > more feature bits. Both QEMUs should first handshake on the feature bits > > they support and enable only the subset that all support. > > > > Or instead of bit, feature strings, etc. would all work which you > > prefer. Just to say we don't need to impl all the ideas there, as some of > > them might take more time (e.g. device tree check), and that list is > > probably not complete anyway. > > While writing a qtest for cpr-transfer, I discovered a problem that could be > solved with an early migration handshake, prior to cpr_save_state / cpr_load_state. > > There is currently no way to set migration caps on dest qemu before starting > cpr-transfer, because dest qemu blocks in cpr_state_load before creating any > devices or monitors. It is unblocked after the user sends the migrate command > to source qemu, but then the migration starts and it is too late to set migration > capabilities or parameters on the dest. > > Are you OK with that restriction (for now, until a handshake is implemented)? > If not, I have a problem. > > I can hack the qtest to make it work with the restriction. Hmm, the test case is one thing, but if it's a problem, then.. how in real life one could set migration capabilities on dest qemu for cpr-transfer? Now a similar question, and also what I overlooked previously, is how cpr-transfer should support "-incoming defer". We need that because that's what Libvirt uses.. with an upcoming migrate_incoming QMP command. -- Peter Xu