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 CC43FC43219 for ; Tue, 26 Oct 2021 15:38:04 +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 5DF8A61090 for ; Tue, 26 Oct 2021 15:38:04 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.1 mail.kernel.org 5DF8A61090 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]:46408 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1mfOWZ-0006jt-2a for qemu-devel@archiver.kernel.org; Tue, 26 Oct 2021 11:38:03 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:47206) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1mfOHx-0003Df-35 for qemu-devel@nongnu.org; Tue, 26 Oct 2021 11:22:57 -0400 Received: from us-smtp-delivery-124.mimecast.com ([216.205.24.124]:29017) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1mfOHu-0007EM-JJ for qemu-devel@nongnu.org; Tue, 26 Oct 2021 11:22:56 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1635261772; 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=vEafkYo5GS2bbKRwA9csOWQPLnc+axtDJd94lzNcqQw=; b=SgOXEb6Bf3TXATDa8zdKpEPMw/djD+aowGEx+xBSaN4JrpvIxcnqkPwEc2zmLuYLsdoADx 7f6DdccJ1Ugc6BwO8Jr4sPj3CNl7uQDlF5tq9fM86IC8KNl6mgN5HmW6wTbpuWlzjnNoZX W0Hex7ZWfLfMYAe8KeJeXq6y3MjywYc= 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-593-b_SiCkkTMsOMcoTiwowJjg-1; Tue, 26 Oct 2021 11:22:49 -0400 X-MC-Unique: b_SiCkkTMsOMcoTiwowJjg-1 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 mimecast-mx01.redhat.com (Postfix) with ESMTPS id 6497F1808302; Tue, 26 Oct 2021 15:22:48 +0000 (UTC) Received: from redhat.com (unknown [10.39.194.218]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 914D85DEFB; Tue, 26 Oct 2021 15:22:45 +0000 (UTC) Date: Tue, 26 Oct 2021 16:22:43 +0100 From: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= 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> <87a6ivg6m9.fsf@dusky.pond.sub.org> MIME-Version: 1.0 In-Reply-To: <87a6ivg6m9.fsf@dusky.pond.sub.org> User-Agent: Mutt/2.0.7 (2021-05-04) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.14 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=berrange@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit Received-SPF: pass client-ip=216.205.24.124; envelope-from=berrange@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=unavailable 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: , Reply-To: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= 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" On Tue, Oct 26, 2021 at 05:15:10PM +0200, Markus Armbruster wrote: > Daniel P. Berrangé writes: > > > On Tue, Oct 26, 2021 at 11:37:19AM +0200, Markus Armbruster wrote: > >> 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. > > > > We will sometimes ignore/forget the feature flag too though, so I'm > > not convinced there's much difference there. > > -compat unstable-input=reject,unstable-output=hide should help you stay > on the straight & narrow :) That's from the pov of the mgmt app. I meant from the POV of QEMU maintainers forgetting to add "unstable" flag, just as they might forget to add a "x-" prefix. 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 :|