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=-12.4 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,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 2AD9DC433E1 for ; Wed, 19 Aug 2020 20:01:32 +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 E80012078D for ; Wed, 19 Aug 2020 20:01:31 +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="PZ/hDZqN" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org E80012078D 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]:57614 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1k8UH5-00018W-69 for qemu-devel@archiver.kernel.org; Wed, 19 Aug 2020 16:01:31 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:53396) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1k8UFw-0000Ry-QA for qemu-devel@nongnu.org; Wed, 19 Aug 2020 16:00:20 -0400 Received: from us-smtp-delivery-1.mimecast.com ([207.211.31.120]:51294 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 1k8UFt-0004lE-Gz for qemu-devel@nongnu.org; Wed, 19 Aug 2020 16:00:20 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1597867216; 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=H6qQIjl0fjMGp3iigdQ/Q7pl1sy0GxaPjwH1a94aV98=; b=PZ/hDZqNtYYYjPJTvHHN6TrjDWPMi6zon6mFiw6+6r20hOzn/9mxlX2QgBUCKRbIVjXTwY djz/GgffkPamGE9eGHHyk9sVriTEtfLFoHkaus2PTKa0EPTG+PtSnRBeW0txC6e3nlK29L EPOcIcIIxKpDTJYEF2pFQSXnYpXzXdY= 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-179-bn_OjaImN2ag7MKfBAl-RA-1; Wed, 19 Aug 2020 16:00:14 -0400 X-MC-Unique: bn_OjaImN2ag7MKfBAl-RA-1 Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.phx2.redhat.com [10.5.11.15]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 881AF1885D87; Wed, 19 Aug 2020 20:00:10 +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 2D5937DFFA; Wed, 19 Aug 2020 20:00:10 +0000 (UTC) Subject: Re: [RFC PATCH 08/22] nbd: Add max-connections to nbd-server-start To: Kevin Wolf , qemu-block@nongnu.org References: <20200813162935.210070-1-kwolf@redhat.com> <20200813162935.210070-9-kwolf@redhat.com> From: Eric Blake Organization: Red Hat, Inc. Message-ID: <973cb8f5-b042-fa70-da45-0aefeaad2fcd@redhat.com> Date: Wed, 19 Aug 2020 15:00:09 -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: <20200813162935.210070-9-kwolf@redhat.com> Content-Language: en-US X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=eblake@redhat.com X-Mimecast-Spam-Score: 0.001 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit 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=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: qemu-devel@nongnu.org, mreitz@redhat.com Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 8/13/20 11:29 AM, Kevin Wolf wrote: > This is a QMP equivalent of qemu-nbd's --share option, limiting the > maximum number of clients that can attach at the same time. > > Signed-off-by: Kevin Wolf > --- > qapi/block-export.json | 10 ++++++++-- > include/block/nbd.h | 3 ++- > block/monitor/block-hmp-cmds.c | 2 +- > blockdev-nbd.c | 33 ++++++++++++++++++++++++++------- > qemu-storage-daemon.c | 4 ++-- > 5 files changed, 39 insertions(+), 13 deletions(-) > > diff --git a/qapi/block-export.json b/qapi/block-export.json > index 40369814b4..1fdc55c53a 100644 > --- a/qapi/block-export.json > +++ b/qapi/block-export.json > @@ -14,6 +14,8 @@ > # is only resolved at time of use, so can be deleted and > # recreated on the fly while the NBD server is active. > # If missing, it will default to denying access (since 4.0). > +# @max-connections: The maximum number of connections to allow at the same > +# time, 0 for unlimited. (since 5.2; default: 0) Nice way to add feature parity. Limiting the number of connections (particularly for a writable client, where we cannot guarantee cache consistency between the connections), seems like a worthwhile feature to have; I've always found it odd that qemu-nbd and QMP nbd-server-add defaulted to different limits (1 vs. unlimited). For reference, nbdkit defaults to unlimited, and I'm happy if qemu-storage-daemon does likewise; but changing qemu-nbd's default of 1 would be backwards incompatible and may cause surprises (there's always 'qemu-nbd -e' when needed). I also wonder if we should change 'qemu-nbd -e 0' to mean unlimited rather than an error (right now, qemu-iotests/common.rc uses -e 42 for all nbd-based tests for a saner limit than just 1, but it smells of being arbitrary compared to unlimited). Reviewed-by: Eric Blake -- Eric Blake, Principal Software Engineer Red Hat, Inc. +1-919-301-3226 Virtualization: qemu.org | libvirt.org