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=-15.1 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,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 9DD76C433EF for ; Tue, 14 Sep 2021 15:36:36 +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 3CEA4604D1 for ; Tue, 14 Sep 2021 15:36:36 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.1 mail.kernel.org 3CEA4604D1 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]:42832 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1mQAU7-0005BZ-DE for qemu-devel@archiver.kernel.org; Tue, 14 Sep 2021 11:36:35 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:48372) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1mQ9nA-0005LO-Ph for qemu-devel@nongnu.org; Tue, 14 Sep 2021 10:52:12 -0400 Received: from us-smtp-delivery-124.mimecast.com ([216.205.24.124]:43531) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1mQ9n5-0001tx-SC for qemu-devel@nongnu.org; Tue, 14 Sep 2021 10:52:12 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1631631125; 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=iyjjglx3RnrC5CzQunCAg3CWJLlEZFUYItPoDzNBKMc=; b=PSZbp/U5Dk3W4vEfGFLRm1PLcujOvwbexI3oiDYsEhShqGGIx8oye1UprtIvt47+ry1Djz DFViDUu/vHNDF+/eeguXyRjaO8/3sZVxH/1k1Cksl93TgLIYSmjLHPb0PNaHvXwKkNF2qz GHGdbR+UYmE6Zsh87How88X2xlJZ2Hc= 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-559-dFBM6DAZMCmHeoJ9NS9Ohg-1; Tue, 14 Sep 2021 10:52:02 -0400 X-MC-Unique: dFBM6DAZMCmHeoJ9NS9Ohg-1 Received: from smtp.corp.redhat.com (int-mx04.intmail.prod.int.phx2.redhat.com [10.5.11.14]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 7AEB4802934; Tue, 14 Sep 2021 14:52:01 +0000 (UTC) Received: from localhost (unknown [10.39.192.185]) by smtp.corp.redhat.com (Postfix) with ESMTP id 29C665D9CA; Tue, 14 Sep 2021 14:52:00 +0000 (UTC) Date: Tue, 14 Sep 2021 15:52:00 +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: <20210914145200.GJ26415@redhat.com> References: <20210913151936.392705-1-rjones@redhat.com> <6c59b070-b9b4-6ecb-8557-3ea54af3d45a@virtuozzo.com> MIME-Version: 1.0 In-Reply-To: <6c59b070-b9b4-6ecb-8557-3ea54af3d45a@virtuozzo.com> User-Agent: Mutt/1.5.21 (2010-09-15) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.14 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-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, T_SPF_TEMPERROR=0.01 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 Tue, Sep 14, 2021 at 05:40:59PM +0300, Vladimir Sementsov-Ogievskiy wrote: > 13.09.2021 18:19, Richard W.M. Jones wrote: > >$ rm -f /tmp/sock /tmp/pid > >$ qemu-img create -f qcow2 /tmp/disk.qcow2 1M > >$ qemu-nbd -t --format=qcow2 --socket=/tmp/sock --pid-file=/tmp/pid /tmp/disk.qcow2 & > >$ nbdsh -u 'nbd+unix:///?socket=/tmp/sock' -c 'h.get_size()' > >qemu-nbd: Disconnect client, due to: Failed to send reply: Unable to write to socket: Broken pipe > >$ killall qemu-nbd > > > >nbdsh is abruptly dropping the NBD connection here which is a valid > >way to close the connection. It seems unnecessary to print an error > >in this case so this commit suppresses it. > > > >Note that if you call the nbdsh h.shutdown() method then the message > >was not printed: > > > >$ nbdsh -u 'nbd+unix:///?socket=/tmp/sock' -c 'h.get_size()' -c 'h.shutdown()' > > My personal opinion, is that this warning doesn't hurt in general. I > think in production tools should gracefully shutdown any connection, > and abrupt shutdown is a sign of something wrong - i.e., worth > warning. > > Shouldn't nbdsh do graceful shutdown by default? On the client side the only difference is that nbd_shutdown sends NBD_CMD_DISC to the server (versus simply closing the socket). 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 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. > >Signed-off-by: Richard W.M. Jones > >--- > > nbd/server.c | 7 ++++++- > > 1 file changed, 6 insertions(+), 1 deletion(-) > > > >diff --git a/nbd/server.c b/nbd/server.c > >index 3927f7789d..e0a43802b2 100644 > >--- a/nbd/server.c > >+++ b/nbd/server.c > >@@ -2669,7 +2669,12 @@ static coroutine_fn void nbd_trip(void *opaque) > > ret = nbd_handle_request(client, &request, req->data, &local_err); > > } > > if (ret < 0) { > >- error_prepend(&local_err, "Failed to send reply: "); > >+ if (errno != EPIPE) { > > Both nbd_handle_request() and nbd_send_generic_reply() declares that > they return -errno on failure in communication with client. I think, > you should use ret here: if (ret != -EPIPE). It's safer: who knows, > does errno really set on all error paths of called functions? If > not, we may see here errno of some another previous operation. Should we set errno = 0 earlier in nbd_trip()? I don't really know how coroutines in qemu interact with thread-local variables though. Rich. > >+ error_prepend(&local_err, "Failed to send reply: "); > >+ } else { > >+ error_free(local_err); > >+ local_err = NULL; > >+ } > > goto disconnect; > > } > > > > > -- > 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-p2v converts physical machines to virtual machines. Boot with a live CD or over the network (PXE) and turn machines into KVM guests. http://libguestfs.org/virt-v2v