From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-10.8 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 32A04C433E0 for ; Thu, 18 Feb 2021 16:11:38 +0000 (UTC) Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 68F5F64E85 for ; Thu, 18 Feb 2021 16:11:37 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 68F5F64E85 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([::1]:34612 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1lCltw-0004QL-3h for qemu-devel@archiver.kernel.org; Thu, 18 Feb 2021 11:11:36 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]:51088) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1lClsf-0003sz-62 for qemu-devel@nongnu.org; Thu, 18 Feb 2021 11:10:17 -0500 Received: from us-smtp-delivery-124.mimecast.com ([63.128.21.124]:47473) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_CBC_SHA1:256) (Exim 4.90_1) (envelope-from ) id 1lClsc-00079c-BQ for qemu-devel@nongnu.org; Thu, 18 Feb 2021 11:10:16 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1613664612; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=n33/NSoHK6zp31Y7N5nc2PoW/HfyV3ag5Yesa8cptjY=; b=CLnTQcAReXsbqEQuG/m1rx9sahdxypqyevMCwIuQ+Mw4dI/Y+V8f+fb3STse2GlyPmMGTT broZn6vaa9xP630va3VkxvdXbmRYByDDII++oF3bh7qgFPWsK1vx/d8F56FxBVaBV/GVPl /dYI/HteDhHJua3B3MiUIj5QJDuhF5w= 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-442-HJnBDLRaPrKcyIw3-g592Q-1; Thu, 18 Feb 2021 11:10:10 -0500 X-MC-Unique: HJnBDLRaPrKcyIw3-g592Q-1 Received: from smtp.corp.redhat.com (int-mx07.intmail.prod.int.phx2.redhat.com [10.5.11.22]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 7AF011005501 for ; Thu, 18 Feb 2021 16:10:09 +0000 (UTC) Received: from merkur.fritz.box (ovpn-113-86.ams2.redhat.com [10.36.113.86]) by smtp.corp.redhat.com (Postfix) with ESMTPS id A49CC10023B4; Thu, 18 Feb 2021 16:10:08 +0000 (UTC) Date: Thu, 18 Feb 2021 17:10:07 +0100 From: Kevin Wolf To: Markus Armbruster Subject: Re: [PATCH v2 4/6] qapi: Apply aliases in qobject-input-visitor Message-ID: <20210218161007.GA10998@merkur.fritz.box> References: <20210211183118.422036-1-kwolf@redhat.com> <20210211183118.422036-5-kwolf@redhat.com> <871rder9py.fsf@dusky.pond.sub.org> <20210217175026.GC5662@merkur.fritz.box> <87o8ghebrb.fsf@dusky.pond.sub.org> MIME-Version: 1.0 In-Reply-To: <87o8ghebrb.fsf@dusky.pond.sub.org> X-Scanned-By: MIMEDefang 2.84 on 10.5.11.22 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=63.128.21.124; envelope-from=kwolf@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -27 X-Spam_score: -2.8 X-Spam_bar: -- X-Spam_report: (-2.8 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, 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_H4=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: jsnow@redhat.com, qemu-devel@nongnu.org Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" Am 18.02.2021 um 14:39 hat Markus Armbruster geschrieben: > Kevin Wolf writes: > > > Am 17.02.2021 um 16:32 hat Markus Armbruster geschrieben: > >> Kevin Wolf writes: > >> > >> > When looking for an object in a struct in the external representation, > >> > check not only the currently visited struct, but also whether an alias > >> > in the current StackObject matches and try to fetch the value from the > >> > alias then. Providing two values for the same object through different > >> > aliases is an error. > >> > > >> > Signed-off-by: Kevin Wolf > >> > >> Looking just at qobject_input_try_get_object() for now. > > > > :-( > > > > This patch doesn't even feel that complicated to me. > > I suspect it's just me having an unusually obtuse week. > > The code is straightforward enough. What I'm missing is a bit of "how > does this accomplish the goal" and "why is this safe" here and there. > > > Old: Get the value from the QDict of the current StackObject with the > > given name. > > > > New: First do alias resolution (with find_object_member), which results > > in a StackObject and a name, and that's the QDict and key where you get > > the value from. > > This part I understand. > > We simultaneously walk the QAPI type and the input QObject, consuming > input as we go. > > Whenever the walk leaves a QAPI object type, we check the corresponding > QObject has been consumed completely. > > With aliases, we additionally look for input in a certain enclosing > input object (i.e. up the recursion stack). If found, consume. > > > Minor complication: Aliases can refer to members of nested objects that > > may not be provided in the input. But we want these to work. > > > > For example, my chardev series defines aliases to flatten > > SocketAddressLegacy (old syntax, I haven't rebased it yet): > > > > { 'union': 'SocketAddressLegacy', > > 'data': { > > 'inet': 'InetSocketAddress', > > 'unix': 'UnixSocketAddress', > > 'vsock': 'VsockSocketAddress', > > 'fd': 'String' }, > > 'aliases': [ > > {'source': ['data']}, > > {'alias': 'fd', 'source': ['data', 'str']} > > ]} > > > > Of course, the idea is that this input should work: > > > > { 'type': 'inet', 'hostname': 'localhost', 'port': '1234' } > > > > However, without implicit objects, parsing 'data' fails because it > > expects an object, but none is given (we specified all of its members on > > the top level through aliases). What we would have to give is: > > > > { 'type': 'inet', 'hostname': 'localhost', 'port': '1234', 'data': {} } > > > > And _that_ would work. Visiting 'data' succeeds because we now have the > > object that the visitor expects, and when visiting its members, the > > aliases fill in all of the mandatory values. > > > > So what this patch does is to implicitly assume the 'data': {} instead > > of erroring out when we know that aliases exist that can still provide > > values for the content of 'data'. > > Aliases exist than can still provide, but will they? What if input is > > {"type": "inet"} > > ? > > Your explanation makes me guess this is equivalent to > > {"type": "inet", "data": {}} > > which fails the visit, because mandatory members of "data" are missing. > Fine. Okay, if you want the gory details, then the answer is yes for this case, but it depends. If we're aliasing a single member, then we can easily check whether the alias is actually specified. If it's not in the input, no implicit object. But in our example, it is a wildcard alias and we don't know yet which aliases it will use. This depends on what the visitor for the implicit object will do (future tense). > If we make the members optional, it succeeds: qobject_input_optional() > checks both the regular and the aliased input, finds neither, and > returns false. Still fine. > > What if "data" is optional, too? Hmmm... Yes, don't use optional objects in the middle of the path of a wildcard alias unless there is no semantic difference between empty object and absent object. This is documented in the code, but it might actually still be missing from qapi-code-gen.txt. > Example: > > { 'struct': 'Outer', > 'data': { '*inner': 'Inner' }, > > { 'struct': 'Inner', > 'data': { '*true-name': 'str' } } > > For input {}, we get an Outer object with > > .has_inner = false, > .inner = NULL > > Now add > > 'aliases': [ { 'name': 'alias-name', > 'source': [ 'inner', 'true-name' ] } ] } > > What do we get now? Is it > > .has_inner = true, > .inner = { .has_true_name = false, > .true_name = NULL } > > perhaps? I think this is the result you would get if you had used a wildcard alias. But since you used a single-member alias, we would see that 'alias-name' is not in the input and actually still return the original result: .has_inner = false, .inner = NULL Kevin