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=-10.2 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,NICE_REPLY_A, 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 23B13C4363A for ; Mon, 26 Oct 2020 13:07:38 +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 5BA9A205CA for ; Mon, 26 Oct 2020 13:07:37 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="WpIiq8E1" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 5BA9A205CA 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]:38368 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1kX2Do-0005r1-Fy for qemu-devel@archiver.kernel.org; Mon, 26 Oct 2020 09:07:36 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:56336) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1kX2Cb-0004WG-HA for qemu-devel@nongnu.org; Mon, 26 Oct 2020 09:06:22 -0400 Received: from us-smtp-delivery-124.mimecast.com ([216.205.24.124]:22578) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_CBC_SHA1:256) (Exim 4.90_1) (envelope-from ) id 1kX2CZ-0003EC-4a for qemu-devel@nongnu.org; Mon, 26 Oct 2020 09:06:20 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1603717577; 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=OTfWbqjLzW/vn2DRWdq8fgN/6ZpNDgAsTGWUU3b7GLM=; b=WpIiq8E1ekZHrkyhOGnIEjoLgcebydxhk18v0VawOHk9uXKFBQqUehdC72MwvGif8Xa8qH j85EEpSYWi7hSjKIU10EfA5mW84czX6XWCd4y1xpmgpCP6SBI4e09vqgbTgCDSh8rof88D a/WOSb2s/JrOa6xPT655EGj+x/ZNJYU= 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-353-tAZcKCE5N2SR0W_KXm4RHQ-1; Mon, 26 Oct 2020 09:06:13 -0400 X-MC-Unique: tAZcKCE5N2SR0W_KXm4RHQ-1 Received: from smtp.corp.redhat.com (int-mx08.intmail.prod.int.phx2.redhat.com [10.5.11.23]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 4CF62A0C01; Mon, 26 Oct 2020 13:06:12 +0000 (UTC) Received: from [10.3.112.145] (ovpn-112-145.phx2.redhat.com [10.3.112.145]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 7E19419728; Mon, 26 Oct 2020 13:06:05 +0000 (UTC) To: Peter Krempa References: <20201023183652.478921-1-eblake@redhat.com> <20201023183652.478921-7-eblake@redhat.com> <20201026105039.GC727443@angien.pipo.sk> From: Eric Blake Organization: Red Hat, Inc. Subject: Re: [PATCH v5 06/12] nbd: Update qapi to support exporting multiple bitmaps Message-ID: <8f898aa0-11f3-019b-5da7-5ffdce2972bb@redhat.com> Date: Mon, 26 Oct 2020 08:06:05 -0500 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.3.1 MIME-Version: 1.0 In-Reply-To: <20201026105039.GC727443@angien.pipo.sk> X-Scanned-By: MIMEDefang 2.84 on 10.5.11.23 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=eblake@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Received-SPF: pass client-ip=216.205.24.124; envelope-from=eblake@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/10/26 02:39:09 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] X-Spam_score_int: -42 X-Spam_score: -4.3 X-Spam_bar: ---- X-Spam_report: (-4.3 / 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, NICE_REPLY_A=-2.167, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H4=0.001, RCVD_IN_MSPIKE_WL=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: kwolf@redhat.com, vsementsov@virtuozzo.com, qemu-block@nongnu.org, "reviewer:Incompatible changes" , qemu-devel@nongnu.org, Markus Armbruster , stefanha@redhat.com, Max Reitz Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 10/26/20 5:50 AM, Peter Krempa wrote: > On Fri, Oct 23, 2020 at 13:36:46 -0500, Eric Blake wrote: >> Since 'nbd-server-add' is deprecated, and 'block-export-add' is new to >> 5.2, we can still tweak the interface. Allowing 'bitmaps':['str'] is >> nicer than 'bitmap':'str'. This wires up the qapi and qemu-nbd >> changes to permit passing multiple bitmaps as distinct metadata >> contexts that the NBD client may request, but the actual support for >> more than one will require a further patch to the server. >> >> Signed-off-by: Eric Blake >> Reviewed-by: Vladimir Sementsov-Ogievskiy >> --- >> +++ b/qapi/block-export.json >> @@ -74,10 +74,10 @@ >> # @description: Free-form description of the export, up to 4096 bytes. >> # (Since 5.0) >> # >> -# @bitmap: Also export the dirty bitmap reachable from @device, so the >> -# NBD client can use NBD_OPT_SET_META_CONTEXT with the >> -# metadata context name "qemu:dirty-bitmap:NAME" to inspect the >> -# bitmap. (since 4.0) >> +# @bitmaps: Also export each of the named dirty bitmaps reachable from >> +# @device, so the NBD client can use NBD_OPT_SET_META_CONTEXT with >> +# the metadata context name "qemu:dirty-bitmap:BITMAP" to inspect >> +# each bitmap. (since 5.2) > > Given unsynchronised release cycles between qemu and management apps > it's not cool to deprecate an interface without having at least one > release where the replacement interface is already stable. > That's why I'm trying as hard as possible to get the block-export-add interface perfect in its 5.2 release; if we agree that allowing qemu to expose more than one bitmap is beneficial (and I argue that it is), then the new interface MUST support that from the get-go, and not something where we release it with 5.2 having 'bitmap' and 6.0 adding 'bitmaps'. > This means that any project wanting to stay up to date will either have > to use deprecated interfaces for at least one release and develop the > replacement only when there's a stable interface or hope that they don't > have to change the interfaces too often. > > This specifically impacts libvirt as we have validators which notify us > that a deprecated interface is used and we want to stay in sync, so that > there's one less group of users to worry about at the point qemu will > want to delete the interface. The deprecated interface is nbd-server-add; for _that_ interface, the 'bitmap' parameter will continue to work until nbd-server-add is removed in 6.1 (so you have all of 5.2 and 6.0 to switch from nbd-server-add to block-export-add). What this patch does, then, is alter the deprecation from merely changing the command from nbd-server-add to block-export-add with all parameter names remaining the same, to instead changing both the command name and the 'bitmap'=>'bitmaps' parameter. But I agree that libvirt wants to do an all-or-none conversion: there is no reason for libvirt to use block-export-add until 5.2 is actually released, at which point we have locked in the new interface; and this patch is a demonstration that we are still debating about a tweak to that interface before it becomes locked in. > >> # @allocation-depth: Also export the allocation depth map for @device, so >> # the NBD client can use NBD_OPT_SET_META_CONTEXT with >> @@ -88,7 +88,7 @@ >> ## >> { 'struct': 'BlockExportOptionsNbd', >> 'data': { '*name': 'str', '*description': 'str', >> - '*bitmap': 'str', '*allocation-depth': 'bool' } } >> + '*bitmaps': ['str'], '*allocation-depth': 'bool' } } > > This adds 'bitmaps' also to nbd-server-add, which should not happen. You > probably want to stop using 'base' for 'NbdServerAddOptions' and just > duplicate everything else. I can respin this to NOT add 'bitmaps' to the legacy 'nbd-server-add', if you think that would be better. It is more complex in the QAPI code, but not too much more difficulty in the glue code; and the glue code all goes away in 6.1 when the deprecation cycle ends. > >> # @NbdServerAddOptions: >> @@ -100,12 +100,18 @@ >> # @writable: Whether clients should be able to write to the device via the >> # NBD connection (default false). >> # >> +# @bitmap: Also export a single dirty bitmap reachable from @device, so the >> +# NBD client can use NBD_OPT_SET_META_CONTEXT with the metadata >> +# context name "qemu:dirty-bitmap:BITMAP" to inspect the bitmap >> +# (since 4.0). Mutually exclusive with @bitmaps, and newer >> +# clients should use that instead. > > This doesn't make sense, nbd-server-add never had @bitmaps. Also adding > features to a deprecated interface doesn't IMO make sense if you want to > motivate users switch to thne new one. Fair enough. v6 coming up later today. -- Eric Blake, Principal Software Engineer Red Hat, Inc. +1-919-301-3226 Virtualization: qemu.org | libvirt.org