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Thu, 21 Jan 2021 08:23:05 +0100 (CET) From: Markus Armbruster To: John Snow Subject: Re: [PATCH v3 05/17] qapi: pass QAPISchemaModule to visit_module instead of str References: <20210119180242.1570753-1-jsnow@redhat.com> <20210119180242.1570753-6-jsnow@redhat.com> <87eeifu805.fsf@dusky.pond.sub.org> <3e43fe6d-b718-af82-598e-e277f9104cbc@redhat.com> <000bd3b7-1342-d26a-5cc9-3191efe0b0ec@redhat.com> Date: Thu, 21 Jan 2021 08:23:05 +0100 In-Reply-To: <000bd3b7-1342-d26a-5cc9-3191efe0b0ec@redhat.com> (John Snow's message of "Wed, 20 Jan 2021 11:16:19 -0500") Message-ID: <87ft2ulpnq.fsf@dusky.pond.sub.org> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/27.1 (gnu/linux) MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 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=216.205.24.124; envelope-from=armbru@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -29 X-Spam_score: -3.0 X-Spam_bar: --- X-Spam_report: (-3.0 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.167, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_LOW=-0.7, 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: =?utf-8?Q?Marc-Andr=C3=A9?= Lureau , qemu-devel@nongnu.org, Eduardo Habkost , Cleber Rosa Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" John Snow writes: > On 1/20/21 11:02 AM, Eric Blake wrote: >> On 1/20/21 6:07 AM, Markus Armbruster wrote: >>> John Snow writes: >>> >>>> Modify visit_module to pass the module itself instead of just its >>>> name. This allows for future patches to centralize some >>>> module-interrogation behavior within the QAPISchemaModule class itself, >>>> cutting down on duplication between gen.py and schema.py. >>> >>> We've been tempted to make similar changes before (don't worry, I'm not >>> building a case for "no" here). >>> >>> When I wrote the initial version of QAPISchemaVisitor (commit 3f7dc21be, >>> 2015), I aimed for a loose coupling of backends and the internal >>> representation. Instead of >>> >>> def visit_foo(self, foo): >>> pass >>> >>> where @foo is a QAPISchemaFooBar, I wrote >>> >>> def visit_foo_bar(self, name, info, [curated attributes of @foo]): >>> pass >>> >>> In theory, this is nice: the information exposed to the backends is >>> obvious, and the backends can't accidentally mutate @foo. >>> >>> In practice, it kind of failed right then and there: >>> >>> def visit_object_type(self, name, info, base, members, variants): >>> pass >>> >>> We avoid passing the QAPISchemaObjectType (loose coupling, cool!), only >>> to pass member information as List[QAPISchemaObjectTypeMember]. >>> >>> Morever, passing "curated atttibutes" has led to visit_commands() taking >>> a dozen arguments. Meh. >>> >>> This had made Eric and me wonder whether we should write off the >>> decoupling idea as misguided, and just pass the object instead of >>> "curated attributes", always. Thoughts? >> I'm open to the idea of passing just the larger object instead of >> the >> curated list of relevant attributes. It's a bit more coupling, but I >> don't see any of our qapi code being reused outside its current scope >> where the extra coupling will bite us. But I'm not volunteering for the >> refactoring work, because I'm not an expert on python typing hints. If >> consolidating parameters into the larger object makes for fewer >> parameters and easier typing hints, I'm assuming the work can be done as >> part of static typing; but if leaving things as they currently are is >> manageable, that's also fine by me. >> > > Yeah, it can definitely be left as-is for now. I've already gone > through all the effort of typing out all of the interfaces, so it's > not really a huge ordeal to just leave it as-is. > > Passing the objects might be nicer for the future, though, as routing > new information or features will involve less churn. (And the > signatures will be a lot smaller.) > > I suppose it does open us up to callers mutating the schema in the > visitors, but they could already do that for the reasons that Markus > points out. It's possible that the visitor dispatch could be modified > to make deep copies of schema objects, but that adds overhead. > > I can just revert this change for now and leave the topic for another day. Works for me. Thanks!