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 Received: from lists1p.gnu.org (lists1p.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 2CEBAC9830E for ; Fri, 25 Sep 2026 21:02:09 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists1p.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1xAD2u-0001JD-Fs; Fri, 25 Sep 2026 17:01:28 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]) by lists1p.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1xAD2r-0001J1-GK for qemu-devel@nongnu.org; Fri, 25 Sep 2026 17:01:25 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1xAD2p-0003Mx-3U for qemu-devel@nongnu.org; Fri, 25 Sep 2026 17:01:25 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1790370081; 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=KNKvk9neUFUjldqAP4KN3NwRY7XmTXLkqg8BuEaVLpA=; b=ePQ7h/oeDpaudvMmX1wTI3EOqpQMziOvFNDZLFmIqlSOiQ5q2j1eS9zcQQEbJw2IYeJ9qF CF9SNQUnrzTYcPHuho3FX+j+98BgGj30dJUVQuM2oH3Wb0uNC2fUU8P9dy6psGzTHcfZ3A D5WRLrMReJ3YT51ZO/WskN2d7Ia6Psc= Received: from mx-prod-mc-08.mail-002.prod.us-west-2.aws.redhat.com (ec2-35-165-154-97.us-west-2.compute.amazonaws.com [35.165.154.97]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-693-xBHG9eNyNROjoZ31oQ7LMw-1; Fri, 25 Sep 2026 17:00:14 -0400 X-MC-Unique: xBHG9eNyNROjoZ31oQ7LMw-1 X-Mimecast-MFC-AGG-ID: xBHG9eNyNROjoZ31oQ7LMw_1790370013 Received: from mx-prod-int-05.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-05.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.17]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mx-prod-mc-08.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 3C35918BA35A; Fri, 25 Sep 2026 21:00:12 +0000 (UTC) Received: from redhat.com (unknown [10.2.16.3]) by mx-prod-int-05.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 8E3E2195604D; Fri, 25 Sep 2026 21:00:09 +0000 (UTC) Date: Fri, 25 Sep 2026 16:00:06 -0500 From: Eric Blake To: Guillaume Vincke Cc: qemu-devel@nongnu.org, qemu-block@nongnu.org, Vladimir Sementsov-Ogievskiy , Kevin Wolf , Hanna Reitz Subject: Re: [PATCH 1/2] nbd/client-connection: Fix client returning a closed channel Message-ID: References: <20260925155346.357703-1-guillaume.vincke@ovhcloud.com> <20260925155346.357703-2-guillaume.vincke@ovhcloud.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260925155346.357703-2-guillaume.vincke@ovhcloud.com> User-Agent: NeoMutt/20260616 X-Scanned-By: MIMEDefang 3.0 on 10.30.177.17 Received-SPF: pass client-ip=170.10.133.124; envelope-from=eblake@redhat.com; helo=us-smtp-delivery-124.mimecast.com 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_H3=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_PASS=-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: 2.1.29 Precedence: list List-Id: qemu development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org On Fri, Sep 25, 2026 at 05:53:45PM +0200, Guillaume Vincke wrote: > When a server closes the connection after a successful handshake but > before running any operations, the channel returned by > nbd_co_establish_connection() is the closed one and the connect thread > is not started. > > When configured with reconnect-delay=0 (the default), this situation > generates at least two IO errors. The first one happens when trying to > issue an operation to the closed socket. The connect thread will be > started on the next request, which may happen long after, and will > create the second error as nbd_co_establish_connection() returns a NULL > channel. > > Peeking the channel to detect FIN or RST avoids the first IO error and > does not delay the starting of the connect thread. > > Signed-off-by: Guillaume Vincke > --- > nbd/client-connection.c | 35 +++++++++++++++++++++++++++++++++++ > 1 file changed, 35 insertions(+) > > diff --git a/nbd/client-connection.c b/nbd/client-connection.c > index 6a4f080717..878219fede 100644 > --- a/nbd/client-connection.c > +++ b/nbd/client-connection.c > @@ -274,6 +274,26 @@ void nbd_client_connection_release(NBDClientConnection *conn) > } > } > > +/* only true when the peer closed the channel. Does not detect if dead */ For consistent style, I would use /* Only true when the peer closed the channel. Does not detect if dead. */ > +static bool nbd_channel_is_closed(QIOChannel *ioc) > +{ > + char data; > + struct iovec iov = { .iov_base = &data, .iov_len = 1 }; > + ssize_t len = -1; > + > + if (!qio_channel_has_feature(ioc, QIO_CHANNEL_FEATURE_READ_MSG_PEEK)) { > + return false; > + } > + > + len = qio_channel_readv_full( > + ioc, &iov, 1, NULL, NULL, QIO_CHANNEL_READ_FLAG_MSG_PEEK, NULL); > + > + if (len == 0 || (len < 0 && len != QIO_CHANNEL_ERR_BLOCK)) { > + return true; > + } > + return false; The last group could be shortened to: return len == 0 || (len < 0 && len != QIO_CHANNEL_ERR_BLOCK); but that is not mandatory. Reviewed-by: Eric Blake -- Eric Blake, Principal Software Engineer Red Hat, Inc. Virtualization: qemu.org | libguestfs.org