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[79.176.44.197]) by smtp.gmail.com with ESMTPSA id w12sm5091891wre.57.2020.12.08.10.48.13 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 08 Dec 2020 10:48:14 -0800 (PST) Date: Tue, 8 Dec 2020 13:48:12 -0500 From: "Michael S. Tsirkin" To: Daniel =?iso-8859-1?Q?P=2E_Berrang=E9?= Subject: Re: [PATCH v2 01/27] migration: Network Failover can't work with a paused guest Message-ID: <20201208134711-mutt-send-email-mst@kernel.org> References: <20201202061641-mutt-send-email-mst@kernel.org> <20201202112639.GE2360260@redhat.com> <20201202063656-mutt-send-email-mst@kernel.org> <20201202120121.GF2360260@redhat.com> <20201203061907-mutt-send-email-mst@kernel.org> <20201203113253.GD2952498@redhat.com> <20201203063452-mutt-send-email-mst@kernel.org> <20201203114341.GB2919@work-vm> <20201203070339-mutt-send-email-mst@kernel.org> <20201203121624.GG2952498@redhat.com> MIME-Version: 1.0 In-Reply-To: <20201203121624.GG2952498@redhat.com> Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=mst@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit Received-SPF: pass client-ip=216.205.24.124; envelope-from=mst@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: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Eduardo Habkost , Juan Quintela , Jason Wang , qemu-devel@nongnu.org, "Dr. David Alan Gilbert" , Paolo Bonzini Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Thu, Dec 03, 2020 at 12:16:24PM +0000, Daniel P. Berrangé wrote: > On Thu, Dec 03, 2020 at 07:11:17AM -0500, Michael S. Tsirkin wrote: > > On Thu, Dec 03, 2020 at 11:43:41AM +0000, Dr. David Alan Gilbert wrote: > > > Another way to solve this would be to remove the unplugging from the > > > migration layer and leave it as a problem for the management layer to do > > > the unplug. > > > > Daniel described the problem with modular management tools which expect > > pausing or slowing down guest to cause migration to converge. > > > > Point is, it actually *will* make it converge but only if you > > pause it after unplug. > > > > As it is, these tools fundamentally can not handle failover > > requiring guest cooperation. Moving code between layers won't help. > > Introducing failure modes as this patch does won't help either > > especially since Daniel wrote there are countless tools like this. > > We just break them all but have no resources to fix them, > > this does not help at all. > > > > We can just leave the situation as is. > > > > Or if we do want to be nice to these tools, how about we > > unpause the guest until unplug, then pause it again? > > This actually addresses the problem instead of > > shifting the blame, does it not? > > This is a very bad idea because it changes the execution status of the > guest behind the apps/admins back, and that cannot be assumed to be a > safe thing todo. > > Regards, > Daniel My question is this: management gets an error since guest was paused presumably by someone (admin?) outside its control. How does it know when it is unpaused? > -- > |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| > |: https://libvirt.org -o- https://fstop138.berrange.com :| > |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|