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=-16.0 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, MENTIONS_GIT_HOSTING,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 3790FC433DF for ; Fri, 9 Oct 2020 09:04:47 +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 9015921D43 for ; Fri, 9 Oct 2020 09:04:46 +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="W1E6tjVR" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 9015921D43 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]:60562 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1kQoKT-0005ET-1e for qemu-devel@archiver.kernel.org; Fri, 09 Oct 2020 05:04:45 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:54308) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1kQoJb-0004ji-MH for qemu-devel@nongnu.org; Fri, 09 Oct 2020 05:03:51 -0400 Received: from us-smtp-delivery-124.mimecast.com ([216.205.24.124]:54878) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_CBC_SHA1:256) (Exim 4.90_1) (envelope-from ) id 1kQoJX-0000Pi-Tv for qemu-devel@nongnu.org; Fri, 09 Oct 2020 05:03:51 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1602234226; 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=40BLIpHmpxJ0tmZvEbnZG0e27rsaUOb3kN365+FYWOw=; b=W1E6tjVRMU3Am81/nGT/4NtqgNCdGXJ/+5bq0PfSQem/9S+mHGiT0MnOy5QtS/A7EV5TfR dblZT3tB3c9QwLTUXOinzsr5WNDAN1dhaVLG0xKOYwsAde4hN9OxkkAZnh/onQrBIfjUda XaP0uFrPoFx58ABUQLEMrMoWwxRIU24= 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-347-iF00IfEAP3-0Gb9yuz_E4g-1; Fri, 09 Oct 2020 05:03:43 -0400 X-MC-Unique: iF00IfEAP3-0Gb9yuz_E4g-1 Received: from smtp.corp.redhat.com (int-mx07.intmail.prod.int.phx2.redhat.com [10.5.11.22]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 8CD75101FFA5; Fri, 9 Oct 2020 09:03:42 +0000 (UTC) Received: from localhost (ovpn-114-98.ams2.redhat.com [10.36.114.98]) by smtp.corp.redhat.com (Postfix) with ESMTP id 5045E10002A4; Fri, 9 Oct 2020 09:03:39 +0000 (UTC) Date: Fri, 9 Oct 2020 10:03:38 +0100 From: "Richard W.M. Jones" To: Markus Armbruster Subject: Re: [PATCH v3 2/6] nbd: Add 'qemu-nbd -A' to expose allocation depth Message-ID: <20201009090338.GE30079@redhat.com> References: <20201009020714.1074061-1-eblake@redhat.com> <20201009020714.1074061-3-eblake@redhat.com> <87lfgfom51.fsf@dusky.pond.sub.org> MIME-Version: 1.0 In-Reply-To: <87lfgfom51.fsf@dusky.pond.sub.org> User-Agent: Mutt/1.5.21 (2010-09-15) X-Scanned-By: MIMEDefang 2.84 on 10.5.11.22 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=rjones@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=216.205.24.124; envelope-from=rjones@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/10/09 02:34:37 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 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_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=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: , Cc: kwolf@redhat.com, vsementsov@virtuozzo.com, qemu-block@nongnu.org, qemu-devel@nongnu.org, Max Reitz , stefanha@redhat.com Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Fri, Oct 09, 2020 at 10:10:18AM +0200, Markus Armbruster wrote: > Eric Blake writes: > > > Allow the server to expose an additional metacontext to be requested > > by savvy clients. qemu-nbd adds a new option -A to expose the > > qemu:allocation-depth metacontext through NBD_CMD_BLOCK_STATUS; this > > can also be set via QMP when using block-export-add. > > > > qemu as client can be hacked into viewing this new context by using > > the now-misnamed x-dirty-bitmap option when creating an NBD blockdev > > (even though our x- naming means we could rename it, I did not think > > it worth breaking back-compat of tools that have been using it while > > waiting for a better solution). It is worth noting the decoding of > > how such context information will appear in 'qemu-img map > > --output=json': > > > > NBD_STATE_DEPTH_UNALLOC => "zero":false, "data":true > > NBD_STATE_DEPTH_LOCAL => "zero":false, "data":false > > NBD_STATE_DEPTH_BACKING => "zero":true, "data":true > > > > libnbd as client is probably a nicer way to get at the information > > without having to decipher such hacks in qemu as client. ;) > > > > Signed-off-by: Eric Blake > > Message-Id: <20200930121105.667049-6-eblake@redhat.com> > > Reviewed-by: Vladimir Sementsov-Ogievskiy > > [eblake: comment tweak suggested by Vladimir] > > Signed-off-by: Eric Blake > > --- > [...] > > diff --git a/qapi/block-core.json b/qapi/block-core.json > > index 3758ea991269..249bd434f4eb 100644 > > --- a/qapi/block-core.json > > +++ b/qapi/block-core.json > > @@ -3882,9 +3882,12 @@ > > # > > # @tls-creds: TLS credentials ID > > # > > -# @x-dirty-bitmap: A "qemu:dirty-bitmap:NAME" string to query in place of > > +# @x-dirty-bitmap: A metacontext name such as "qemu:dirty-bitmap:NAME" or > > What is a "metacontext"? > > Aside: nbd.h spells it "meta context". The two spellings suggest > different meanings to me. Using meta- as a prefix modifies the prefixed > word, as in metadata (data that provides information about other data). > Separated by space, meta becomes a noun. None of its common meanings > seem to apply here. Recommend to pick an appropriate one of > "metacontext", "meta-context", "meta context", and stick to it. In the NBD protocol it's called a "metadata context". This is abbreviated to "...META_CONTEXT" in the names of constants, eg. NBD_OPT_SET_META_CONTEXT. For the reasons you gave I don't think it's a very good name, but it's what we have. https://github.com/NetworkBlockDevice/nbd/blob/master/doc/proto.md#metadata-querying What it actually is, is a string, like "base:allocation" or "qemu:dirty-bitmap:" which selects which metadata you want to query in NBD_CMD_BLOCK_STATUS commands. Rich. -- Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones Read my programming and virtualization blog: http://rwmj.wordpress.com virt-df lists disk usage of guests without needing to install any software inside the virtual machine. Supports Linux and Windows. http://people.redhat.com/~rjones/virt-df/