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[188.85.150.151]) by smtp.gmail.com with ESMTPSA id o19-20020a05600c4fd300b004060f0a0fd5sm1654414wmq.13.2023.10.17.07.11.18 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 17 Oct 2023 07:11:18 -0700 (PDT) From: Juan Quintela To: "Michael S. Tsirkin" Cc: qemu-devel@nongnu.org, Leonardo Bras , Peter Xu , Jiri Denemark , Avihai Horon , Fiona Ebner , Daniel P . =?utf-8?Q?Berrang=C3=A9?= Subject: Re: [PATCH v3 2/3] migration/docs: How to migrate when hosts have different features In-Reply-To: <20230517062128-mutt-send-email-mst@kernel.org> (Michael S. Tsirkin's message of "Wed, 17 May 2023 06:23:26 -0400") References: <20230515083201.55060-1-quintela@redhat.com> <20230515083201.55060-3-quintela@redhat.com> <20230517062128-mutt-send-email-mst@kernel.org> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/28.3 (gnu/linux) Date: Tue, 17 Oct 2023 16:11:18 +0200 Message-ID: <87wmvlz6d5.fsf@secure.mitica> MIME-Version: 1.0 Content-Type: text/plain Received-SPF: pass client-ip=170.10.133.124; envelope-from=quintela@redhat.com; helo=us-smtp-delivery-124.mimecast.com 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_H3=0.001, RCVD_IN_MSPIKE_WL=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: , Reply-To: quintela@redhat.com Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org "Michael S. Tsirkin" wrote: > On Mon, May 15, 2023 at 10:32:00AM +0200, Juan Quintela wrote: >> Sometimes devices have different features depending of things outside >> of qemu. For instance the kernel. Document how to handle that cases. >> >> Signed-off-by: Juan Quintela > > yes, e.g. vhost features are exactly like this. Yeap, I know that. But not in enough detail to get a good example. [...] >> +In this section we have considered that we are using the same QEMU >> +binary in both sides of the migration. If we use different QEMU >> +versions process, then we need to have into account all other >> +differences and the examples become even more complicated. > > How do people know what to do? They need to: - know their hardware/device/driver. - how they can do it in qemu. I can help with the second, not with the 1st. > How about a tool that will help you get data from hosts > and then tell you how to configure qemu to make them > compatible? This is the holy gray of migration. I would like to be able to create machines from QMP. That way, I can transport the configuration over the migration channel, instead of hoping that it is the same. Troubles so far: - we are very far away of being able to create machines with QMP (not migration related). - we have properties that can be different on source and destination. For instance, the path to the file that implements a device can be different on both systems. We could add some keyword to the part of the configuration that can be different. As said, we can say that destination/QMP can give us a new path for a block device. But we need to be able to mark number of CPU's as required to be the same. - For devices/state that can't be seen from inside qemu, I don't know have a good idea. It can be related that I am not an expert on that type of devices. Perhaps someone that knows more about they can give some insights. Later, Juan.