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 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 smtp.lore.kernel.org (Postfix) with ESMTPS id DA430C433F5 for ; Tue, 10 May 2022 10:22:56 +0000 (UTC) Received: from localhost ([::1]:45674 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1noN15-0003ec-MV for qemu-devel@archiver.kernel.org; Tue, 10 May 2022 06:22:55 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:35324) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1noMpU-0000nO-7O for qemu-devel@nongnu.org; Tue, 10 May 2022 06:10:56 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]:36491) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1noMpR-00082P-Rs for qemu-devel@nongnu.org; Tue, 10 May 2022 06:10:55 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1652177452; h=from:from:reply-to: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=5407T1nhVDz0ycKzR+0Tfj2tnb/MkAKBxK1Z1597Bi4=; b=ZglmfXyHVTaPARJ2GPPwlb1T5JqC6miYGfmQQnoM6airm0J6bJZmQ1kFJ5nx6wvRHqNvaG tvq6adpZCv51KdHTn88Y4elRPNfDd2C+XdGD02RvfVL45uuu1Jyd8dswGeh+GcndIP9rWe E6IZILyqSOu2nSWHV5ygaO+TjOchkUU= Received: from mimecast-mx02.redhat.com (mimecast-mx02.redhat.com [66.187.233.88]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-460-HkLKLSwdO66krURd1dBdrw-1; Tue, 10 May 2022 06:10:51 -0400 X-MC-Unique: HkLKLSwdO66krURd1dBdrw-1 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.rdu2.redhat.com [10.11.54.3]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 96D63811E75 for ; Tue, 10 May 2022 10:10:51 +0000 (UTC) Received: from redhat.com (unknown [10.33.36.168]) by smtp.corp.redhat.com (Postfix) with ESMTPS id AF42A111E411; Tue, 10 May 2022 10:10:47 +0000 (UTC) Date: Tue, 10 May 2022 11:10:45 +0100 From: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= To: Victor Toso Cc: qemu-devel@nongnu.org, John Snow , Eric Blake , Markus Armbruster Subject: Re: [RFC PATCH v1 2/8] qapi: golang: Generate qapi's alternate types in Go Message-ID: References: <20220401224104.145961-1-victortoso@redhat.com> <20220401224104.145961-3-victortoso@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20220401224104.145961-3-victortoso@redhat.com> User-Agent: Mutt/2.1.5 (2021-12-30) X-Scanned-By: MIMEDefang 2.78 on 10.11.54.3 Received-SPF: pass client-ip=170.10.133.124; envelope-from=berrange@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -28 X-Spam_score: -2.9 X-Spam_bar: -- X-Spam_report: (-2.9 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.082, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_LOW=-0.7, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, T_SCC_BODY_TEXT_LINE=-0.01 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Reply-To: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Sat, Apr 02, 2022 at 12:40:58AM +0200, Victor Toso wrote: > This patch handles QAPI alternate types and generates data structures > in Go that handles it. > > At this moment, there are 5 alternates in qemu/qapi, they are: > * BlockDirtyBitmapMergeSource > * Qcow2OverlapChecks > * BlockdevRef > * BlockdevRefOrNull > * StrOrNull > > Alternate types are similar to Union but without a discriminator that > can be used to identify the underlying value on the wire. It is needed > to infer it. That can't be easily mapped in Go. I don't buy that. Given this example: type BlockdevRef struct { // Options are: // * definition (BlockdevOptions): defines a new block device inline // * reference (string): references the ID of an existing block device Value Any } What is the problem with having this Go struct: type BlockdevRef struct { Definition *BlockdevOptions Reference *string } when deserializing from JSON, we know exactly which one of these two fields to populate. The programmer consuming this can look at which field is non-nil. When serializing to JSON, we serialize which ever field is non-nil. If both fields are non-nil that's a programmer bug. Either ignore it and only serialize the first non-nil field, or raise an error. > > For each Alternate type, we will be using a Any type to hold the > value. 'Any' is an alias type for interface{} (similar to void* in C). > > Similarly to the Enum types (see previous commit), we will implement > Marshaler and Unmarshaler interfaces for the Alternate types and in > those MarshalJSON() and UnmarshalJSON() methods is where we are going > to put the logic to read/set alternate's value. > > Note that on UnmarshalJSON(), a helper function called StrictDecode() > will be used. This function is the main logic to infer if a given JSON > object fits in a given Go struct. Because we only have 5 alternate > types, it is not hard to validate the unmarshaling logic but we might > need to improve it in the future if Alternate with branches that have > similar fields appear. > > Examples: > * BlockdevRef > ```go > // Data to set in BlockdevOptions > qcow2 := BlockdevOptionsQcow2{} > // BlockdevRef using a string > qcow2.File = BlockdevRef{Value: "/some/place/my-image"} > opt := BlockdevOptions{} > opt.Driver = BlockdevDriverQcow2 > opt.Value = qcow2 > > b, _ := json.Marshal(data.s) > // string(b) == `{"driver":"qcow2","file":"/some/place/my-image"}` > ``` > > Signed-off-by: Victor Toso > --- > scripts/qapi/golang.py | 157 ++++++++++++++++++++++++++++++++++++++++- > 1 file changed, 155 insertions(+), 2 deletions(-) With regards, Daniel -- |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o- https://fstop138.berrange.com :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|