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 042B9C433EF for ; Wed, 11 May 2022 16:33:20 +0000 (UTC) Received: from localhost ([::1]:54944 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1nopH5-0000vw-Mc for qemu-devel@archiver.kernel.org; Wed, 11 May 2022 12:33:19 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:44954) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1nopG5-0000Ep-2b for qemu-devel@nongnu.org; Wed, 11 May 2022 12:32:17 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]:44077) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1nopG1-00015r-QN for qemu-devel@nongnu.org; Wed, 11 May 2022 12:32:15 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1652286732; 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: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=320EZiwka2d8lnwj59ys+EM4iUYo1xmwUxNUvjlLf5o=; b=ajpElyaRntF/f0h2RhpwZCkpG27gsb9kJPqG7etsl4CEdGSlWfX6z1KEG1PziEXxM+dd1N br2wP9wf4p1SWGbyOsgIvA/LWdmQabX16+VYAgJOLzIbr2KeOTdBfeqiBYEjce9y6gZTO0 B6UI8G3gq09y7QdbGIftQ/pBoqz0DPk= Received: from mimecast-mx02.redhat.com (mx3-rdu2.redhat.com [66.187.233.73]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-656-5cnCkiq5NWSGkQLi7q-PBw-1; Wed, 11 May 2022 12:32:08 -0400 X-MC-Unique: 5cnCkiq5NWSGkQLi7q-PBw-1 Received: from smtp.corp.redhat.com (int-mx08.intmail.prod.int.rdu2.redhat.com [10.11.54.8]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 998BB3C32313 for ; Wed, 11 May 2022 16:32:08 +0000 (UTC) Received: from redhat.com (unknown [10.33.36.142]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 5983DC28125; Wed, 11 May 2022 16:32:07 +0000 (UTC) Date: Wed, 11 May 2022 17:32:04 +0100 From: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= To: Andrea Bolognani Cc: Markus Armbruster , Victor Toso , John Snow , Eric Blake , qemu-devel@nongnu.org, =?utf-8?Q?Marc-Andr=C3=A9?= Lureau Subject: Re: [RFC PATCH v1 0/8] qapi: add generator for Golang interface Message-ID: References: <20220401224104.145961-1-victortoso@redhat.com> <87bkwonlkb.fsf@pond.sub.org> <87lev9mw7j.fsf@pond.sub.org> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: User-Agent: Mutt/2.1.5 (2021-12-30) X-Scanned-By: MIMEDefang 2.85 on 10.11.54.8 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 Wed, May 11, 2022 at 09:22:36AM -0700, Andrea Bolognani wrote: > On Wed, May 11, 2022 at 04:50:35PM +0100, Daniel P. Berrangé wrote: > > This would lead to a situation where every struct is duplicated > > for every version, even though 90% of the time they'll be identical > > across multiple versions. This is not very ammenable to the desire > > to be able to dynamically choose per-command which version you > > want based on which version of QEMU you're connected to. > > > > ie > > > > var cmd Command > > if qmp.HasVersion(qemu.Version(7, 0, 0)) { > > cmd = BlockResizeArguments{ > > V700: &BlockResizeArguments700{ > > NodeName: node, > > Size: 1 * GiB > > } > > } > > } else { > > cmd = BlockResizeArguments{ > > V520: &BlockResizeArguments520{ > > Device: dev, > > Size: 1 * GiB > > } > > } > > } > > > > And of course the HasVersion check is going to be different > > for each command that matters. > > > > Having said that, this perhaps shows the nested structs are > > overkill. We could have > > > > var cmd Command > > if qmp.HasVersion(qemu.Version(7, 0, 0)) { > > cmd = &BlockResizeArguments700{ > > NodeName: node, > > Size: 1 * GiB > > } > > } else { > > cmd = &BlockResizeArguments520{ > > Device: dev, > > Size: 1 * GiB > > } > > } > > Right, making the decision at the import level would require adding a > level of indirection and make this kind of dynamic logic awkward. > > We shouldn't force users to sprinkle version numbers everywhere > though, especially since different commands will change at different > points in time. It should be possible to do something like > > if !qmp.HasAPI(600) { > panic("update QEMU") > } > > cmd := &BlockResizeArguments600{ // really BlockResizeArguments520 > Device: device, > Size: size, > } > > or even > > if !qmp.HasAPI(qmp.API.Latest) { > panic("update QEMU") > } > > cmd := &BlockResizeArguments{ > NodeName: nodeName, > Size: size, > } > > Should be easy enough to achieve with type aliases. I guess we would have a single package which does typedef BlockResizeArguments520 BlockResizeArguments; ...for each type... The interaction with API versioning will be tedious though. For the versioned structs we'll be forever back compatible, due to the append-only nature of the versioned struct approach. For the type aliases, we'll be forever breaking compat as at least 1 struct alias is likely to need changing every QEMU release. Might suggest having 2 distinct go modules. A base module which is versioned as a stable API with semver (forever v1.xxx), and an add-on module that depends on base module, which is versioned as an unstable API with semver (forever v0.xxx) 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 :|