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=-10.0 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, MENTIONS_GIT_HOSTING,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 4D698C433EF for ; Wed, 15 Sep 2021 09:03:44 +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 0F00661214 for ; Wed, 15 Sep 2021 09:03:44 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.1 mail.kernel.org 0F00661214 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]:39214 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1mQQpT-0008Bv-33 for qemu-devel@archiver.kernel.org; Wed, 15 Sep 2021 05:03:43 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:48328) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1mQQmV-00063O-I8 for qemu-devel@nongnu.org; Wed, 15 Sep 2021 05:00:40 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]:55763) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1mQQmN-0001YU-VT for qemu-devel@nongnu.org; Wed, 15 Sep 2021 05:00:39 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1631696431; 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=ScQreEvlUnZODc+46+HapyUOFyzdcB6Hso9m98nJU0Q=; b=PJSzyMKbvz0/FHj+uthryXb5ptQxCS0yowX1JDHaTnOLf3GIcGJt7bKL0fho+tmYZNcB89 /uzUXscZ88j6XFNWCXjwSRFEqcFzGmhCpDF0j67cnpxy+GF/lHWKGvIm2R7L7CZhfB8vo3 OvWLjNV+CAxIKkt93HqrmJ7foFCuQDM= 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-530-b7pEkshnOnSmaLuOB5ybAg-1; Wed, 15 Sep 2021 05:00:27 -0400 X-MC-Unique: b7pEkshnOnSmaLuOB5ybAg-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 BFAC41B18BC5; Wed, 15 Sep 2021 09:00:26 +0000 (UTC) Received: from localhost (unknown [10.39.192.185]) by smtp.corp.redhat.com (Postfix) with ESMTP id 6DC91100EBBE; Wed, 15 Sep 2021 09:00:25 +0000 (UTC) Date: Wed, 15 Sep 2021 10:00:25 +0100 From: "Richard W.M. Jones" To: Vladimir Sementsov-Ogievskiy Subject: Re: [PATCH v2] nbd/server: Suppress Broken pipe errors on abrupt disconnection Message-ID: <20210915090025.GP26415@redhat.com> References: <20210913151936.392705-1-rjones@redhat.com> <6c59b070-b9b4-6ecb-8557-3ea54af3d45a@virtuozzo.com> <20210914145200.GJ26415@redhat.com> <997fe8b4-3610-2336-c7f3-67a0e2cbf34e@virtuozzo.com> <20210914163232.GN26415@redhat.com> <0bdef3d9-df05-f49d-038c-9930c2677f54@virtuozzo.com> MIME-Version: 1.0 In-Reply-To: <0bdef3d9-df05-f49d-038c-9930c2677f54@virtuozzo.com> 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=170.10.133.124; envelope-from=rjones@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -31 X-Spam_score: -3.2 X-Spam_bar: --- X-Spam_report: (-3.2 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.398, 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: , Cc: kwolf@redhat.com, eblake@redhat.com, qemu-devel@nongnu.org, qemu-block@nongnu.org Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Wed, Sep 15, 2021 at 10:15:20AM +0300, Vladimir Sementsov-Ogievskiy wrote: > 14.09.2021 19:32, Richard W.M. Jones wrote: > >On Tue, Sep 14, 2021 at 06:21:58PM +0300, Vladimir Sementsov-Ogievskiy wrote: > >>14.09.2021 17:52, Richard W.M. Jones wrote: > >>>On the > >>>server side when the server receives NBD_CMD_DISC it must complete any > >>>in-flight requests, but there's no requirement for the server to > >>>commit anything to disk. IOW you can still lose data even though you > >>>took the time to disconnect. > >>> > >>>So I don't think there's any reason for libnbd to always gracefully > >> > >>Hmm. Me go to NBD spec :) > >> > >>I think, there is a reason: > >> > >>"The client and the server MUST NOT initiate any form of disconnect other than in one of the above circumstances." > >> > >>And the only possibility for client to initiate a hard disconnect listed above is "if it detects a violation by the other party of a mandatory condition within this document". > >> > >>So at least, nbdsh violates NBD protocol. May be spec should be updated to satisfy your needs. > > > >I would say the spec is at best contradictory, but if you read other > >parts of the spec, then it's pretty clear that we're allowed to drop > >the connection whenever we like. This section says as much: > > > >https://github.com/NetworkBlockDevice/nbd/blob/5805b25ad3da96e7c0b3160cda51ea19eb518d5b/doc/proto.md#terminating-the-transmission-phase > > Hmm, that was exactly the section I read and quoted :) > > > > > There are two methods of terminating the transmission phase: > > ... > > "The client or the server drops the TCP session (in which case it > > SHOULD shut down the TLS session first). This is referred to as > > 'initiating a hard disconnect'." > > Right. Here the method is defined, no word that client can do it at any time. I don't read this as a definition. But we should probably clarify the spec to note that dropping the connection is fine, because it is - no one has made any argument so far that there's an actual reason to waste time on NBD_CMD_DISC. Rich. > Next, in same section: > > Either side MAY initiate a hard disconnect if it detects a violation by the other party of a mandatory condition within this document. > > Next > The client MAY issue a soft disconnect at any time > > And finally: > > The client and the server MUST NOT initiate any form of disconnect other than in one of the above circumstances. > > > Or do you mean some other spec section I missed? > > > > >Anyway we're dropping the TCP connection because sometimes we are just > >interrogating an NBD server eg to find out what it supports, and doing > >a graceful shutdown is a waste of time and internet. > > > >>>shut down (especially in this case where there are no in-flight > >>>requests), and anyway it would break ABI to make that change and slow > >>>down the client in cases when there's nothing to clean up. > >> > >>Which ABI will it break? > > > >Our contract with callers using nbd_close(3), if nbd_shutdown(3) is > >not called beforehand. > >https://libguestfs.org/nbd_shutdown.3.html > >https://libguestfs.org/nbd_create.3.html (really nbd_close ...) > > > >Rich. > > > > > -- > Best regards, > Vladimir -- 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. 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