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 91D2FC433F5 for ; Tue, 26 Oct 2021 11:37:09 +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 2E35B604E9 for ; Tue, 26 Oct 2021 11:37:09 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.1 mail.kernel.org 2E35B604E9 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]:49982 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1mfKlQ-0000Ek-BJ for qemu-devel@archiver.kernel.org; Tue, 26 Oct 2021 07:37:08 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:38834) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1mfKjo-0007PS-Hh for qemu-devel@nongnu.org; Tue, 26 Oct 2021 07:35:35 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]:39839) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1mfKjl-00035Z-Tz for qemu-devel@nongnu.org; Tue, 26 Oct 2021 07:35:28 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1635248117; 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=lpbEWU78bohWHVTvzM2t5UCnorufLkWQSfdzo8iRfmU=; b=BzwBcCO3choNmQ7JJQKCnD97GzPiPilTOPAXK7SEDgKDtagmUVL2IkxDEZylIhukZboTe7 Ggc4zgM7IXTBWCsuN8tpqtt7Ot0vBkd1vVTkDUc1UR6iICkN/5IDFXGJhZN9XBDmlqNxdI shVCXCLo0BfEXvPyy1IIhQrabVbwzX4= 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-440-oq6V3S6PPEaXLpA35B6qeQ-1; Tue, 26 Oct 2021 07:35:13 -0400 X-MC-Unique: oq6V3S6PPEaXLpA35B6qeQ-1 Received: from smtp.corp.redhat.com (int-mx02.intmail.prod.int.phx2.redhat.com [10.5.11.12]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 0468E100A640; Tue, 26 Oct 2021 11:35:13 +0000 (UTC) Received: from redhat.com (unknown [10.39.194.70]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 2990D60CC4; Tue, 26 Oct 2021 11:34:35 +0000 (UTC) Date: Tue, 26 Oct 2021 13:34:33 +0200 From: Kevin Wolf To: Markus Armbruster Subject: Re: [PATCH 1/9] qapi: New special feature flag "unstable" Message-ID: References: <20211025052532.3859634-1-armbru@redhat.com> <20211025052532.3859634-2-armbru@redhat.com> <87r1c83z5c.fsf@dusky.pond.sub.org> MIME-Version: 1.0 In-Reply-To: <87r1c83z5c.fsf@dusky.pond.sub.org> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 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=170.10.133.124; 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_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: pkrempa@redhat.com, berrange@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" Am 26.10.2021 um 11:37 hat Markus Armbruster geschrieben: > Kevin Wolf writes: > > > 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. > >> > >> Drawback: promoting something from experimental to stable involves a > >> name change. Client code needs to be updated. > >> > >> Moreover, the convention is not universally observed: > >> > >> * QOM type "input-barrier" has properties "x-origin", "y-origin". > >> Looks accidental, but it's ABI since 4.2. > >> > >> * 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. > >> > >> We could document these exceptions, but documentation helps only > >> humans. We want to recognize "unstable" in code, like "deprecated". > >> > >> 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. > >> > >> This commit updates documentation and prepares tests. The next commit > >> updates the QAPI schema. The remaining patches update the QAPI > >> generator and wire up -compat policy checking. > >> > >> 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 will > > almost certainly go unnoticed in manual use. > > I thought about this, but neglected to put it in writing. My bad. > > Manual use of unstable interfaces is mostly fine. Human users can adapt > to changing interfaces. HMP works that way. > > Management applications are better off with a feature flag than with a > naming convention we sometimes ignore. > > The most potential for trouble is in between: programs that aren't > full-fledged management applications. > > 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... Just to clarify, I'm not implying that we should keep it. I'm merely pointing out that there is a tradeoff that requires us to make a choice. The decision for one of the options should be explicit rather than just happening as a side effect. Documenting that it was a conscious decision is probably best done by adding the reasoning for it to the commit message. > What we can't do, at least not easily, is to use *only* the "x-" > convention: it is not reliable. We'd have to add a way to say 'this is > stable even though the name starts with "x-"'. No question. Kevin