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([2001:b07:6468:f312:c8dd:75d4:99ab:290a]) by smtp.gmail.com with ESMTPSA id z12sm621940ejr.17.2020.12.03.03.11.41 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 03 Dec 2020 03:11:41 -0800 (PST) To: Kevin Wolf , Eduardo Habkost References: <20201201193528.GC6264@merkur.fritz.box> <3449b5d6-d094-84c8-a0ea-4cd25364db2d@redhat.com> <20201201220854.GC3836@habkost.net> <17afbbfe-209f-e4b2-e9e1-b50abe1fce3c@redhat.com> <20201202125124.GD3836@habkost.net> <69dff34f-d87b-3a8d-640f-35f6bf5db75c@redhat.com> <20201202135451.GE3836@habkost.net> <20201202151713.GE16765@merkur.fritz.box> <20201202160554.GG3836@habkost.net> <20201202173506.GH16765@merkur.fritz.box> From: Paolo Bonzini Subject: Re: [PATCH 00/18] qapi/qom: QAPIfy object-add Message-ID: <54637ad5-0662-24ea-d738-1d53e054a103@redhat.com> Date: Thu, 3 Dec 2020 12:11:40 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.4.0 MIME-Version: 1.0 In-Reply-To: <20201202173506.GH16765@merkur.fritz.box> Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=pbonzini@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 8bit Received-SPF: pass client-ip=63.128.21.124; envelope-from=pbonzini@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -35 X-Spam_score: -3.6 X-Spam_bar: --- X-Spam_report: (-3.6 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-1.495, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, NICE_REPLY_A=-0.001, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H4=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=unavailable 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: lvivier@redhat.com, thuth@redhat.com, pkrempa@redhat.com, berrange@redhat.com, qemu-block@nongnu.org, libvir-list@redhat.com, jasowang@redhat.com, armbru@redhat.com, qemu-devel@nongnu.org, kraxel@redhat.com, mreitz@redhat.com Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 02/12/20 18:35, Kevin Wolf wrote: >> Could we have an intermediate state that doesn't require any >> duplication and thus have no separate code paths that could >> diverge? > > The one requirement we have for an intermediate state is that it > supports both interfaces: The well-know create/set properties/realize > dance, and a new DeviceClass method, say .create(), that takes the > configuration in parameters instead of relying on previously set > properties. > > I assumed two separate implementations of transferring the configuration > into the internal state. On second thought, this assumption is maybe > wrong. > > You can implement the new method as wrapper around the old way: It could > just set all the properties and call realize. Of course, you don't win > much in terms of improving the class implementation this way, but just > support the new interface, but I guess it can be a reasonable > intermediate step to resolve complicated dependencies etc. I sketched something at https://wiki.qemu.org/Features/QOM-QAPI_integration. The main difference with what we discussed so far is that it doesn't subsume the complete/realize step, only the setting of properties. The idea is that user_creatable_add_type does the following: - calls an oc->configure method on every superclass of the object - takes what's left of the input visitor and uses it to set properties - then calls ucc->complete So in the end the only new step is the first. If the first two steps are bundled in a new function object_configure, they can be reused for devices, machines and accelerators. The QAPI code generator can also easily wrap them into a C API for QOM object creation. I glossed completely over the generation of properties within the QAPI code generator. Making properties read-only (or, in the field-properties world, having a default allow_set of "return false") is already a nice improvement over > It would be much nicer to do the wrapper the other way round, i.e. > setting properties before the device is realized would update a > configuration struct and realize would then call .create() with that > struct. To me, this sounds much harder, though also a more useful state. This sounds much harder. However, based on the RngEgd sample, going from a basic QAPI struct to a full conversion is not too hard and makes code shorter. So it's win-win even though it's human work. Paolo