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bh=SvUS+RcNRSWm6iC6JHkRs1whGwrng9m4HROzWFe1FpQ=; b=PyU8XgdlfhPj11qM0Cu45iZXpS+kVofzbRrMBSfPDysbDN5z1qbvwOP3g9GBu45swHlinx rmb9CwPeJgRBIyHPCxcBY8EGb03qE8/RsEaO0oE1JbZzvGmbm87n7ZTIKVy2Mmdrf5dOdN pv1g5W8NWKWzYHKGVkY/onRjzwDdY8A= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-321-mckdll2TNvKDL0IWNrIlhw-1; Mon, 15 Mar 2021 11:52:18 -0400 X-MC-Unique: mckdll2TNvKDL0IWNrIlhw-1 Received: from smtp.corp.redhat.com (int-mx01.intmail.prod.int.phx2.redhat.com [10.5.11.11]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id D9FED19057A0; Mon, 15 Mar 2021 15:52:16 +0000 (UTC) Received: from merkur.fritz.box (ovpn-115-128.ams2.redhat.com [10.36.115.128]) by smtp.corp.redhat.com (Postfix) with ESMTPS id CC90B620DE; Mon, 15 Mar 2021 15:52:07 +0000 (UTC) Date: Mon, 15 Mar 2021 16:52:06 +0100 From: Kevin Wolf To: Markus Armbruster Subject: Re: [PATCH v3 00/30] qapi/qom: QAPIfy --object and object-add Message-ID: References: <90130a0c-7f96-f344-b185-b790c5d6b78a@redhat.com> <20210310173044.GF6076@merkur.fritz.box> <87ft12q8kf.fsf@dusky.pond.sub.org> <87h7lhbx6b.fsf@dusky.pond.sub.org> <10fd7cbf-9ee5-3869-22fd-352e42a980ba@redhat.com> <871rck7pqw.fsf@dusky.pond.sub.org> <87lfarrx37.fsf@dusky.pond.sub.org> <87im5se8v4.fsf@dusky.pond.sub.org> MIME-Version: 1.0 In-Reply-To: <87im5se8v4.fsf@dusky.pond.sub.org> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.11 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=kwolf@redhat.com 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=216.205.24.124; envelope-from=kwolf@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=-0.25, 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: lvivier@redhat.com, thuth@redhat.com, Peter Krempa , ehabkost@redhat.com, qemu-block@nongnu.org, libvir-list@redhat.com, jasowang@redhat.com, qemu-devel@nongnu.org, mreitz@redhat.com, kraxel@redhat.com, Paolo Bonzini , dgilbert@redhat.com Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" Am 15.03.2021 um 16:26 hat Markus Armbruster geschrieben: > Kevin Wolf writes: > > > Am 13.03.2021 um 14:40 hat Markus Armbruster geschrieben: > >> Markus Armbruster writes: > >> > >> > Paolo Bonzini writes: > >> > > >> >> On 11/03/21 15:08, Markus Armbruster wrote: > >> >>>> I would rather keep the OptsVisitor here. Do the same check for JSON > >> >>>> syntax that you have in qobject_input_visitor_new_str, and whenever > >> >>>> you need to walk all -object arguments, use something like this: > >> >>>> > >> >>>> typedef struct ObjectArgument { > >> >>>> const char *id; > >> >>>> QDict *json; /* or NULL for QemuOpts */ > >> >>>> QSIMPLEQ_ENTRY(ObjectArgument) next; > >> >>>> } > >> >>>> > >> >>>> I already had patches in my queue to store -object in a GSList of > >> >>>> dictionaries, changing it to use the above is easy enough. > >> >>> > >> >>> I think I'd prefer following -display's precedence. See my reply to > >> >>> Kevin for details. > >> >> > >> >> Yeah, I got independently to the same conclusion and posted patches > >> >> for that. I was scared that visit_type_ObjectOptions was too much for > >> >> OptsVisitor but it seems to work... > >> > > >> > We have reason to be scared. I'll try to cover this in my review. > >> > >> The opts visitor has serious limitations. From its header: > >> > >> * The Opts input visitor does not implement support for visiting QAPI > >> * alternates, numbers (other than integers), null, or arbitrary > >> * QTypes. It also requires a non-null list argument to > >> * visit_start_list(). > >> > >> This is retro-documentation for hairy code. I don't trust it. Commit > >> eb7ee2cbeb "qapi: introduce OptsVisitor" hints at additional > >> restrictions: > >> > >> The type tree in the schema, corresponding to an option with a > >> discriminator, must have the following structure: > >> > >> struct > >> scalar member for non-discriminated optarg 1 [*] > >> list for repeating non-discriminated optarg 2 [*] > >> wrapper struct > >> single scalar member > >> union > >> struct for discriminator case 1 > >> scalar member for optarg 3 [*] > >> list for repeating optarg 4 [*] > >> wrapper struct > >> single scalar member > >> scalar member for optarg 5 [*] > >> struct for discriminator case 2 > >> ... > > > > Is this a long-winded way of saying that it has to be flat, except that > > it allows lists, i.e. there must be no nested objects on the "wire"? > > I think so. > > > The difference between structs and unions, and different branches inside > > the union isn't visible for the visitor anyway. > > Yes, only the code using the visitor deals with that. > > >> The "type" optarg name is fixed for the discriminator role. Its schema > >> representation is "union of structures", and each discriminator value must > >> correspond to a member name in the union. > >> > >> If the option takes no "type" descriminator, then the type subtree rooted > >> at the union must be absent from the schema (including the union itself). > >> > >> Optarg values can be of scalar types str / bool / integers / size. > >> > >> Unsupported visits are treated as programming error. Which is a nice > >> way to say "they crash". > > > > The OptsVisitor never seems to crash explicitly by calling something > > like abort(). > > > > It may crash because of missing callbacks that are called without a NULL > > check, like v->type_null. > > Correct. > > > This case should probably be fixed in > > qapi/qapi-visit-core.c to do the check and simply return an error. > > I retro-documented what I inherited: qapi-visit-core.c code expects the > visitors to implement the full visitor-impl.h interface, but some > visitors don't. So I documented "method must be set to visit FOOs" in > visitor-impl.h, and for the visitors that don't, I documented "can't > visit FOOs". > > If the crashing behavior we've always had gets in the way, there are two > ways to change it: > > 1. Complicate qapi-visit-core.c slightly to cope with incomplete visitor > implementations. > > 2. Complete the visitor implementations: add dummy callbacks that fail. > > I prefer 2., because I feel it keeps the visitor-impl.h interface > simpler, and puts the extra complications where they belong. I suggested making the callbacks optional because I expected that there might be more than one visitor that doesn't support a callback and I wouldn't like duplicating dummy callbacks in multiple places. But if it's only the OptsVisitor, then we wouldn't get any duplication either way and it becomes a matter of taste. Kevin