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 mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 48162C433EF for ; Tue, 26 Oct 2021 15:24:19 +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 D064460E74 for ; Tue, 26 Oct 2021 15:24:18 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.1 mail.kernel.org D064460E74 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=nongnu.org Received: from localhost ([::1]:46432 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1mfOJF-0004Kq-W5 for qemu-devel@archiver.kernel.org; Tue, 26 Oct 2021 11:24:18 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:45368) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1mfOB4-0008FB-6i for qemu-devel@nongnu.org; Tue, 26 Oct 2021 11:15:50 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]:27838) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1mfOB2-0006Dv-FG for qemu-devel@nongnu.org; Tue, 26 Oct 2021 11:15:49 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1635261347; 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: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=XClyofZcaxSOe54dXRPpMgyDh3OxSuvKq2e3pJ+w6oU=; b=Rn/FmhxW1GJRJaJgAI3COuUXqKpZpyljSUKwTf9dEC4LvY/evJ1Yx5PIughmDWuJjiJs87 Z+BDJQcaYUo4rQICl4w7tRhq9hMu99Q1rT4zSzbe0zlkMBGqMWzzp5RN4UnwFViDYxb9cf O2nnNjNB178KNlBZSH5hItREKi03CGg= 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-340-8YARrrL7N1CHohsJtzEnCA-1; Tue, 26 Oct 2021 11:15:46 -0400 X-MC-Unique: 8YARrrL7N1CHohsJtzEnCA-1 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.phx2.redhat.com [10.5.11.13]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 02B6A100B3BA; Tue, 26 Oct 2021 15:15:45 +0000 (UTC) Received: from blackfin.pond.sub.org (ovpn-112-7.ams2.redhat.com [10.36.112.7]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 568E9AFD81; Tue, 26 Oct 2021 15:15:12 +0000 (UTC) Received: by blackfin.pond.sub.org (Postfix, from userid 1000) id A042911380A7; Tue, 26 Oct 2021 17:15:10 +0200 (CEST) From: Markus Armbruster To: Daniel P. =?utf-8?Q?Berrang=C3=A9?= Subject: Re: [PATCH 1/9] qapi: New special feature flag "unstable" References: <20211025052532.3859634-1-armbru@redhat.com> <20211025052532.3859634-2-armbru@redhat.com> <87r1c83z5c.fsf@dusky.pond.sub.org> Date: Tue, 26 Oct 2021 17:15:10 +0200 In-Reply-To: ("Daniel P. =?utf-8?Q?Berrang?= =?utf-8?Q?=C3=A9=22's?= message of "Tue, 26 Oct 2021 15:56:26 +0100") Message-ID: <87a6ivg6m9.fsf@dusky.pond.sub.org> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/27.2 (gnu/linux) MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=armbru@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable Received-SPF: pass client-ip=170.10.133.124; envelope-from=armbru@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_H2=-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: Kevin Wolf , pkrempa@redhat.com, ehabkost@redhat.com, qemu-block@nongnu.org, quintela@redhat.com, libvir-list@redhat.com, eblake@redhat.com, mdroth@linux.vnet.ibm.com, qemu-devel@nongnu.org, dgilbert@redhat.com, pbonzini@redhat.com, marcandre.lureau@redhat.com, jsnow@redhat.com, libguestfs@redhat.com Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" Daniel P. Berrang=C3=A9 writes: > On Tue, Oct 26, 2021 at 11:37:19AM +0200, Markus Armbruster wrote: >> Kevin Wolf writes: >>=20 >> > Am 25.10.2021 um 07:25 hat Markus Armbruster geschrieben: >> >> By convention, names starting with "x-" are experimental. The parts >> >> of external interfaces so named may be withdrawn or changed >> >> incompatibly in future releases. >> >>=20 >> >> Drawback: promoting something from experimental to stable involves a >> >> name change. Client code needs to be updated. >> >>=20 >> >> Moreover, the convention is not universally observed: >> >>=20 >> >> * QOM type "input-barrier" has properties "x-origin", "y-origin". >> >> Looks accidental, but it's ABI since 4.2. >> >>=20 >> >> * QOM types "memory-backend-file", "memory-backend-memfd", >> >> "memory-backend-ram", and "memory-backend-epc" have a property >> >> "x-use-canonical-path-for-ramblock-id" that is documented to be >> >> stable despite its name. >> >>=20 >> >> We could document these exceptions, but documentation helps only >> >> humans. We want to recognize "unstable" in code, like "deprecated". >> >>=20 >> >> Replace the convention by a new special feature flag "unstable". It >> >> will be recognized by the QAPI generator, like the existing feature >> >> flag "deprecated", and unlike regular feature flags. >> >>=20 >> >> This commit updates documentation and prepares tests. The next commi= t >> >> updates the QAPI schema. The remaining patches update the QAPI >> >> generator and wire up -compat policy checking. >> >>=20 >> >> Signed-off-by: Markus Armbruster >> > >> > Obviously, replacing the old convention gets rid of the old drawbacks, >> > but adds a new one: While using x- makes it very obvious for a human >> > user that this is an unstable feature, a feature flag in the schema wi= ll >> > almost certainly go unnoticed in manual use. >>=20 >> I thought about this, but neglected to put it in writing. My bad. >>=20 >> Manual use of unstable interfaces is mostly fine. Human users can adapt >> to changing interfaces. HMP works that way. >>=20 >> Management applications are better off with a feature flag than with a >> naming convention we sometimes ignore. > > We will sometimes ignore/forget the feature flag too though, so I'm > not convinced there's much difference there. -compat unstable-input=3Dreject,unstable-output=3Dhide should help you stay on the straight & narrow :) >> If we want to keep "unstable" obvious to the humans who write such >> programs, we can continue to require "x-", in addition to the feature >> flag. We pay for it with renames, and the risk of forgetting to rename >> in time (which is what got us the awkward stable >> "x-use-canonical-path-for-ramblock-id"). Tradeoff. I chose not to, but >> if y'all think we should... > > IMHO the renames arguably make life easier for mgmt apps, as they > only need to check for the name without the x- prefix, and they > know they won't be accidentally using the fature from an older > QEMU where it was unstable because the older QEMU had a different > name they won't be checking for. > > We can just as easily forget to remove the "unstable" feature > flag, as forget to rename. > > The plus point about the feature flag is that it is aligned with > the "deprecated" feature flag, and potentially aligned with a > future "insecure" feature flag. Yup.