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Mon, 20 Jul 2020 15:59:56 +0000 (UTC) Date: Mon, 20 Jul 2020 11:59:55 -0400 From: Eduardo Habkost To: Markus Armbruster Subject: Re: sysbus_create_simple Vs qdev_create Message-ID: <20200720155955.GV1274972@habkost.net> References: <87365t18mp.fsf@dusky.pond.sub.org> <87lfjkvo81.fsf@dusky.pond.sub.org> <20200716222130.GO1274972@habkost.net> <87tuy6k9pa.fsf@dusky.pond.sub.org> <20200717162312.GR1274972@habkost.net> <87r1t6hc0f.fsf@dusky.pond.sub.org> MIME-Version: 1.0 In-Reply-To: <87r1t6hc0f.fsf@dusky.pond.sub.org> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Received-SPF: pass client-ip=207.211.31.81; envelope-from=ehabkost@redhat.com; helo=us-smtp-delivery-1.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/07/19 21:45:06 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] X-Spam_score_int: -30 X-Spam_score: -3.1 X-Spam_bar: --- X-Spam_report: (-3.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-1, 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=-0.01, RCVD_IN_MSPIKE_WL=-0.01, 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: Paolo Bonzini , Daniel =?iso-8859-1?Q?P=2E_Berrang=E9?= , qemu-devel@nongnu.org, Pratik Parvati , Philippe =?iso-8859-1?Q?Mathieu-Daud=E9?= Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Mon, Jul 20, 2020 at 09:38:24AM +0200, Markus Armbruster wrote: > Eduardo Habkost writes: > > > On Fri, Jul 17, 2020 at 07:10:57AM +0200, Markus Armbruster wrote: > >> Eduardo Habkost writes: > >> > >> > I'd also note that the use of "parent" in the code is also > >> > ambiguous. It can mean: > >> > > >> > * QOM parent type, i.e. TypeInfo.parent. Related fields: > >> > * parent_class members of class structs > >> > * parent_obj members of object structs > >> > >> I hate the use of "parent" and "child" for a super- / subtype relation. > >> > >> Correcting the terminology there would be short term pain for long term > >> gain. Worthwhile? > > > > I don't know. It looks like the terminology came from GObject. > > > >> > >> > * QOM composition tree parent object, i.e. Object::parent > >> > * qdev device parent bus, i.e. DeviceState::parent_bus > >> > * parent device of of qdev bus, i.e. BusState::parent > >> > >> These are tree relations. Use of "parent" and "child" is perfectly > >> fine. > > > > The terms are fine but still ambiguous, as devices belong to two > > separate trees at the same time (the QOM composition tree, and > > the qdev tree). > > > > I never understood why we have two separate independent object > > trees. > > When we rebased qdev onto QOM, we left the qdev tree alone, we did not > embed it into the QOM composition tree. > > The qdev tree edge from bus to device providing the bus is commonly > mirrored in the QOM composition tree: both are QOM objects, and the bus > is commonly a QOM composition child of the device providing it. I hedge > with "commonly", because nothing enforces this as far as I know. > > We do not mirror the edge from device to the bus it's plugged into. I > believe we could have. I guess we could mirror it as a link even now > (but note links are not children). They are already mirrored as links, and guess what's the link name: "child[...]". > > I don't know why the rebase of qdev onto QOM was done that way. Perhaps > Paolo remembers. I'm guessing this is because QOM parent/child relationships represent ownership, while there's no ownership relationship between buses and devices. -- Eduardo