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=-9.7 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,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 362C5C433DF for ; Wed, 19 Aug 2020 20:06:55 +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 00579207FF for ; Wed, 19 Aug 2020 20:06:54 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="F4HH9cye" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 00579207FF 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]:32962 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1k8UMI-0002tn-5a for qemu-devel@archiver.kernel.org; Wed, 19 Aug 2020 16:06:54 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:55094) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1k8ULa-0002N8-MV for qemu-devel@nongnu.org; Wed, 19 Aug 2020 16:06:10 -0400 Received: from us-smtp-delivery-1.mimecast.com ([207.211.31.120]:20288 helo=us-smtp-1.mimecast.com) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_CBC_SHA1:256) (Exim 4.90_1) (envelope-from ) id 1k8ULY-0005bE-7o for qemu-devel@nongnu.org; Wed, 19 Aug 2020 16:06:10 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1597867565; 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=5LNEo8CBejPcYcaSDR4Q+0FOl5DFXVMlySPmB3pX3Yo=; b=F4HH9cyehnH/I3mbpkEO4QUGmjXY8q+AjRRsExAbY1aY22QQj4jD75K/DaToYI4Iy4mDgl 4zKkBluJofdkpTMzvOlFm9m8f4HdCFm5vAUaZlt/Vb9S4Z50P6RLKVfjPp/E9IlCI2s5Aa oXuTauiIHBO4BregB/e2Ky102eBQ5hs= 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-569-8tjLlhgfOQWyx246TC81rQ-1; Wed, 19 Aug 2020 16:06:00 -0400 X-MC-Unique: 8tjLlhgfOQWyx246TC81rQ-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 A02981854FEA; Wed, 19 Aug 2020 20:05:59 +0000 (UTC) Received: from [10.3.112.136] (ovpn-112-136.phx2.redhat.com [10.3.112.136]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 3619560BEC; Wed, 19 Aug 2020 20:05:59 +0000 (UTC) Subject: Re: [RFC PATCH 09/22] nbd: Add writethrough to block-export-add To: Max Reitz , Kevin Wolf , qemu-block@nongnu.org References: <20200813162935.210070-1-kwolf@redhat.com> <20200813162935.210070-10-kwolf@redhat.com> From: Eric Blake Organization: Red Hat, Inc. Message-ID: Date: Wed, 19 Aug 2020 15:05:58 -0500 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.11.0 MIME-Version: 1.0 In-Reply-To: Content-Language: en-US X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=eblake@redhat.com X-Mimecast-Spam-Score: 0.002 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit Received-SPF: pass client-ip=207.211.31.120; envelope-from=eblake@redhat.com; helo=us-smtp-1.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/08/19 16:00:16 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] X-Spam_score_int: -30 X-Spam_score: -3.1 X-Spam_bar: --- X-Spam_report: (-3.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-1, 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_H3=-0.01, RCVD_IN_MSPIKE_WL=-0.01, 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: qemu-devel@nongnu.org Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 8/17/20 7:56 AM, Max Reitz wrote: > On 13.08.20 18:29, Kevin Wolf wrote: >> qemu-nbd allows use of writethrough cache modes, which mean that write >> requests made through NBD will cause a flush before they complete. >> Expose the same functionality in block-export-add. >> >> Signed-off-by: Kevin Wolf >> --- >> +++ b/qapi/block-export.json >> @@ -167,10 +167,15 @@ >> # Describes a block export, i.e. how single node should be exported on an >> # external interface. >> # >> +# @writethrough: If true, caches are flushed after every write request to the >> +# export before completion is signalled. (since: 5.2; >> +# default: false) >> +# >> # Since: 4.2 >> ## >> { 'union': 'BlockExportOptions', >> - 'base': { 'type': 'BlockExportType' }, >> + 'base': { 'type': 'BlockExportType', >> + '*writethrough': 'bool' }, >> 'discriminator': 'type', >> 'data': { >> 'nbd': 'BlockExportOptionsNbd' > > Hm. I find it weird to have @writethrough in the base but @device in > the specialized class. > > I think everything that will be common to all block exports should be in > the base, and that probably includes a node-name. I’m aware that will > make things more tedious in the code, but perhaps it would be a nicer > interface in the end. Or is the real problem that that would create > problems in the storage daemon’s command line interface, because then > the specialized (legacy) NBD interface would no longer be compatible > with the new generalized block export interface? > > Anyway, @writable might be a similar story. A @read-only may make sense > in general, I think. And maybe even auto-read-only. As for @writable vs. @read-only, that's a choice of spelling, but we don't want both; there's also the question of which default is saner (having to opt-in to allowing writes is more verbose than defaulting to allowing writes when possible, but arguably saner as it is less risk of unintended writes when you forgot to specify the option; @auto-read-only can help in choosing nicer defaults). > > Basically, I think that the export code should be separate from the code > setting up the BlockBackend that should be exported, so all options > regarding that BB should be common; and those options are @node-name, > @writethrough, and @read-only. (And perhaps other things like > @resizable, too, even though that isn’t something to consider for NBD.) NBD isn't resizable yet, but extending the protocol to let it become so is on my TODO list. -- Eric Blake, Principal Software Engineer Red Hat, Inc. +1-919-301-3226 Virtualization: qemu.org | libvirt.org