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Thu, 6 Aug 2020 05:58:07 +0000 (UTC) Received: by blackfin.pond.sub.org (Postfix, from userid 1000) id 787DC1132801; Thu, 6 Aug 2020 07:58:06 +0200 (CEST) From: Markus Armbruster To: Eduardo Habkost Subject: Re: [PATCH] ide: Get rid of IDEDrive struct References: <20200805194812.1735218-1-ehabkost@redhat.com> <20200805221417.GC1700540@habkost.net> Date: Thu, 06 Aug 2020 07:58:06 +0200 In-Reply-To: <20200805221417.GC1700540@habkost.net> (Eduardo Habkost's message of "Wed, 5 Aug 2020 18:14:17 -0400") Message-ID: <877ducb9jl.fsf@dusky.pond.sub.org> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/26.3 (gnu/linux) MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=armbru@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain Received-SPF: pass client-ip=205.139.110.61; envelope-from=armbru@redhat.com; helo=us-smtp-delivery-1.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/08/06 00:07:42 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] X-Spam_score_int: -40 X-Spam_score: -4.1 X-Spam_bar: ---- X-Spam_report: (-4.1 / 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_H2=-1, 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: Peter Maydell , =?utf-8?Q?Daniel_P=2E_Berrang=C3=A9?= , Qemu-block , QEMU Developers , Gerd Hoffmann , John Snow Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" Eduardo Habkost writes: > On Wed, Aug 05, 2020 at 09:41:25PM +0100, Peter Maydell wrote: >> On Wed, 5 Aug 2020 at 20:49, Eduardo Habkost wrote: >> > >> > The struct had a single field (IDEDevice dev), and is only used >> > in the QOM type declarations and property lists. We can simply >> > use the IDEDevice struct directly instead. >> > >> > Signed-off-by: Eduardo Habkost >> > @@ -327,7 +323,6 @@ static void ide_hd_class_init(ObjectClass *klass, void *data) >> > static const TypeInfo ide_hd_info = { >> > .name = "ide-hd", >> > .parent = TYPE_IDE_DEVICE, >> > - .instance_size = sizeof(IDEDrive), >> > .class_init = ide_hd_class_init, >> > }; >> >> This is one of those areas where this change works and reduces >> amount of code, but on the other hand it means the QOM type >> doesn't follow the common pattern for a leaf type of: >> * it has a struct >> * it has cast macros that cast to that struct >> * the typeinfo instance_size is the size of that struct >> (it wasn't exactly following this pattern before, of course). > > Is this really a pattern that exists and we want to follow? > I don't see why that pattern would be useful for simple leaf > types. I think the pattern exists, but we deviate from it in quite a few places, probably just because it's so much boilerplate. Related: Daniel's "[PATCH 0/4] qom: reduce boilerplate required for declaring and defining objects". Perhaps Daniel has an opinion on taking shortcuts with leaf types. > Also, in this case the code wasn't even following that pattern: > it was using the same IDEDrive struct for all TYPE_IDE_DEVICE > subtypes. Rule of thumb: hw/ide/ is a bad example. I don't mean to belittle the efforts of quite a few people over the years. It used to be worse. >> We define in https://wiki.qemu.org/Documentation/QOMConventions >> (in the 'When to create class types and macros' bit at the bottom) >> what we expect for whether to provide class cast macros/a >> class struct/class_size in the TypeInfo, essentially recommending >> that types follow one of two patterns (simple leaf class with no >> methods or class members, vs everything else) even if in a >> particular case you could take a short-cut and not define >> everything. We haven't really defined similar "this is the >> standard pattern, provide it all even if you don't strictly >> need it" rules for the instance struct/macros. Maybe we should? > > I think we should include the instance struct/macros in the > recommendations there, but I would expect those recommendations > to apply only to non-leaf types. I'm fine with having a separate convention for leaf types if that helps, but please let's have a convention. I like my QOM boilerplate uncreative. >> Just a thought, not a nak; I know we have quite a number >> of types that take this kind of "we don't really need to >> provide all the standard QOM macros/structs/etc" approach >> (some of which I wrote!). >> >> thanks >> -- PMM >>