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=-5.5 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED, USER_AGENT_SANE_1 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 DE4FAC49ED7 for ; Tue, 10 Sep 2019 16:55:24 +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 B0E232082C for ; Tue, 10 Sep 2019 16:55:24 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org B0E232082C 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]:43434 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1i7jQJ-0000z7-Ru for qemu-devel@archiver.kernel.org; Tue, 10 Sep 2019 12:55:23 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:56053) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1i7jDz-0003YG-AF for qemu-devel@nongnu.org; Tue, 10 Sep 2019 12:42:40 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1i7jDx-000604-VX for qemu-devel@nongnu.org; Tue, 10 Sep 2019 12:42:39 -0400 Received: from mx1.redhat.com ([209.132.183.28]:34874) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1i7jDx-0005zc-Lz for qemu-devel@nongnu.org; Tue, 10 Sep 2019 12:42:37 -0400 Received: from smtp.corp.redhat.com (int-mx04.intmail.prod.int.phx2.redhat.com [10.5.11.14]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id AFB9A300BEAC; Tue, 10 Sep 2019 16:42:36 +0000 (UTC) Received: from [10.3.116.234] (ovpn-116-234.phx2.redhat.com [10.3.116.234]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 4A2A85D9DC; Tue, 10 Sep 2019 16:42:34 +0000 (UTC) To: Markus Armbruster , qemu-devel@nongnu.org References: <20190910063724.28470-1-armbru@redhat.com> <20190910063724.28470-14-armbru@redhat.com> From: Eric Blake Openpgp: preference=signencrypt Autocrypt: addr=eblake@redhat.com; keydata= xsBNBEvHyWwBCACw7DwsQIh0kAbUXyqhfiKAKOTVu6OiMGffw2w90Ggrp4bdVKmCaEXlrVLU xphBM8mb+wsFkU+pq9YR621WXo9REYVIl0FxKeQo9dyQBZ/XvmUMka4NOmHtFg74nvkpJFCD TUNzmqfcjdKhfFV0d7P/ixKQeZr2WP1xMcjmAQY5YvQ2lUoHP43m8TtpB1LkjyYBCodd+LkV GmCx2Bop1LSblbvbrOm2bKpZdBPjncRNob73eTpIXEutvEaHH72LzpzksfcKM+M18cyRH+nP sAd98xIbVjm3Jm4k4d5oQyE2HwOur+trk2EcxTgdp17QapuWPwMfhaNq3runaX7x34zhABEB AAHNHkVyaWMgQmxha2UgPGVibGFrZUByZWRoYXQuY29tPsLAegQTAQgAJAIbAwULCQgHAwUV CgkICwUWAgMBAAIeAQIXgAUCS8fL9QIZAQAKCRCnoWtKJSdDahBHCACbl/5FGkUqJ89GAjeX RjpAeJtdKhujir0iS4CMSIng7fCiGZ0fNJCpL5RpViSo03Q7l37ss+No+dJI8KtAp6ID+PMz wTJe5Egtv/KGUKSDvOLYJ9WIIbftEObekP+GBpWP2+KbpADsc7EsNd70sYxExD3liwVJYqLc Rw7so1PEIFp+Ni9A1DrBR5NaJBnno2PHzHPTS9nmZVYm/4I32qkLXOcdX0XElO8VPDoVobG6 gELf4v/vIImdmxLh/w5WctUpBhWWIfQDvSOW2VZDOihm7pzhQodr3QP/GDLfpK6wI7exeu3P pfPtqwa06s1pae3ad13mZGzkBdNKs1HEm8x6zsBNBEvHyWwBCADGkMFzFjmmyqAEn5D+Mt4P zPdO8NatsDw8Qit3Rmzu+kUygxyYbz52ZO40WUu7EgQ5kDTOeRPnTOd7awWDQcl1gGBXgrkR pAlQ0l0ReO57Q0eglFydLMi5bkwYhfY+TwDPMh3aOP5qBXkm4qIYSsxb8A+i00P72AqFb9Q7 3weG/flxSPApLYQE5qWGSXjOkXJv42NGS6o6gd4RmD6Ap5e8ACo1lSMPfTpGzXlt4aRkBfvb NCfNsQikLZzFYDLbQgKBA33BDeV6vNJ9Cj0SgEGOkYyed4I6AbU0kIy1hHAm1r6+sAnEdIKj cHi3xWH/UPrZW5flM8Kqo14OTDkI9EtlABEBAAHCwF8EGAEIAAkFAkvHyWwCGwwACgkQp6Fr SiUnQ2q03wgAmRFGDeXzc58NX0NrDijUu0zx3Lns/qZ9VrkSWbNZBFjpWKaeL1fdVeE4TDGm I5mRRIsStjQzc2R9b+2VBUhlAqY1nAiBDv0Qnt+9cLiuEICeUwlyl42YdwpmY0ELcy5+u6wz mK/jxrYOpzXKDwLq5k4X+hmGuSNWWAN3gHiJqmJZPkhFPUIozZUCeEc76pS/IUN72NfprZmF Dp6/QDjDFtfS39bHSWXKVZUbqaMPqlj/z6Ugk027/3GUjHHr8WkeL1ezWepYDY7WSoXwfoAL 2UXYsMAr/uUncSKlfjvArhsej0S4zbqim2ZY6S8aRWw94J3bSvJR+Nwbs34GPTD4Pg== Organization: Red Hat, Inc. Message-ID: <60b61f7c-fe08-e78b-dd52-775959af99d9@redhat.com> Date: Tue, 10 Sep 2019 11:42:33 -0500 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.8.0 MIME-Version: 1.0 In-Reply-To: <20190910063724.28470-14-armbru@redhat.com> Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="rTgNV085A5fAp8vdPley3C2BjHEZiKZp0" X-Scanned-By: MIMEDefang 2.79 on 10.5.11.14 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.42]); Tue, 10 Sep 2019 16:42:36 +0000 (UTC) X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] X-Received-From: 209.132.183.28 Subject: Re: [Qemu-devel] [PATCH v2 13/16] docs/devel/qapi-code-gen: Rewrite compatibility considerations 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: marcandre.lureau@redhat.com, mdroth@linux.vnet.ibm.com Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" This is an OpenPGP/MIME signed message (RFC 4880 and 3156) --rTgNV085A5fAp8vdPley3C2BjHEZiKZp0 Content-Type: multipart/mixed; boundary="Y1lvbK758f6qRbHE6aZjNT52jPxyRmqLe"; protected-headers="v1" From: Eric Blake To: Markus Armbruster , qemu-devel@nongnu.org Cc: mdroth@linux.vnet.ibm.com, marcandre.lureau@redhat.com Message-ID: <60b61f7c-fe08-e78b-dd52-775959af99d9@redhat.com> Subject: Re: [PATCH v2 13/16] docs/devel/qapi-code-gen: Rewrite compatibility considerations References: <20190910063724.28470-1-armbru@redhat.com> <20190910063724.28470-14-armbru@redhat.com> In-Reply-To: <20190910063724.28470-14-armbru@redhat.com> --Y1lvbK758f6qRbHE6aZjNT52jPxyRmqLe Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: quoted-printable On 9/10/19 1:37 AM, Markus Armbruster wrote: > We have some compatibility advice buried in sections "Enumeration > types" and "Struct types". Compatibility is actually about commands > and events. It devolves to the types used there. All kinds of types, > not just enumerations and structs. >=20 > Replace the existing advice by a new section "Compatibility > considerations". >=20 > Signed-off-by: Markus Armbruster > --- > docs/devel/qapi-code-gen.txt | 95 +++++++++++++++++++++++-------------= > 1 file changed, 60 insertions(+), 35 deletions(-) >=20 > +=3D=3D Compatibility considerations =3D=3D > + > +Maintaining backward compatibility at the Client JSON Protocol level > +while evolving the schema requires some care. This section is about > +syntactic compatibility. Necessary, but not sufficient for actual > +compatibility. This last sentence no verb. Maybe: s/compatibility. Necessary/compatibility, which is necessary/ s/sufficient/sufficient,/ > + > +Clients send commands with argument data, and receive command > +responses with return data and events with event data. > + > +Adding opt-in functionality to the send direction is backwards > +compatible: adding commands, optional arguments, enumeration values, > +union and alternate branches; turning an argument type into an > +alternate of that type; making mandatory arguments optional. Clients > +oblivious of the new functionality continue to work. > + > +Incompatible changes include removing commands, command arguments, > +enumeration values, union and alternate branches, adding mandatory > +command arguments, and making optional arguments mandatory. > + > +The specified behavior of an absent optional argument should remain > +the same. With proper documentation, this policy still allows some > +flexibility; for example, when an optional 'buffer-size' argument is > +specified to default to a sensible buffer size, the actual default > +value can still be changed. The specified default behavior is not the= > +exact size of the buffer, only that the default size is sensible. > + > +Adding functionality to the receive direction is generally backwards > +compatible: adding events, adding return and event data members. > +Clients are expected to ignore the ones they don't know. > + > +Removing "unreachable" stuff like events that can't be triggered > +anymore, optional return or event data members that can't be sent > +anymore, and return or event data member (enumeration) values that > +can't be sent anymore makes no difference to clients, except for > +introspection. The latter can conceivably confuse clients, so tread > +carefully. > + > +Incompatible changes include removing return and event data members. > + > +Any change to a command definition's 'data' or one of the types used > +there (recursively) needs to consider send direction compatibility. > + > +Any change to a command definition's 'return', an event definition's > +'data', or one of the types used there (recursively) needs to consider= > +receive direction compatibility. > + > +Any change to types used in both contexts need to consider both. > + > +Members of enumeration types, complex types and alternate types may be= > +reordered freely. For enumerations and alternate types, this doesn't > +affect the wire encoding. For complex types, this might make the > +implementation emit JSON object members in a different order, which > +the Client JSON Protocol permits. Worth mentioning that type names themselves are NOT part of the interface, and may be freely renamed? Reviewed-by: Eric Blake --=20 Eric Blake, Principal Software Engineer Red Hat, Inc. +1-919-301-3226 Virtualization: qemu.org | libvirt.org --Y1lvbK758f6qRbHE6aZjNT52jPxyRmqLe-- --rTgNV085A5fAp8vdPley3C2BjHEZiKZp0 Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- iQEzBAEBCAAdFiEEccLMIrHEYCkn0vOqp6FrSiUnQ2oFAl130nkACgkQp6FrSiUn Q2rqSAgAsHdakyxwYhtIvgSgLG2s6sV9bfHR89ZhGSj0yo/uUN2iy/vSugYBZpcj 90Hi8KOO3h2jnXCTKO0SIFV4/w/wCcPdnQ2yqi8j5xmGuhrE6/HPJ0p8RXHNU9nf 4N0SYFjA6ZbKHyEXKU6bYrmqDcY+38V9rXbzZRQek57C3mjUhDYOt/u/vdedkaE5 HBAhF4DWBPKdgDYmY2ntcq8AYBsE9B7lCpihZqInEQH+6Uxx4j9EeK+XWt1gF38h WlM5eapEYMEMep7OgOa3rA/2pfbvPe3oTrY2Y4iobpzzOUIaWpYvlMGYf454ZgfV 3i/13ZytX+90oJMssIMPX0dQVOp5XQ== =x7ZW -----END PGP SIGNATURE----- --rTgNV085A5fAp8vdPley3C2BjHEZiKZp0--