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=-8.0 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,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 4A97DC433E0 for ; Wed, 10 Jun 2020 16:30:20 +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 132AD2072F for ; Wed, 10 Jun 2020 16:30:19 +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="OIi9AH9o" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 132AD2072F 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]:49868 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1jj3cH-0003Yp-Ot for qemu-devel@archiver.kernel.org; Wed, 10 Jun 2020 12:30:17 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:38724) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1jj3bK-0002of-7n for qemu-devel@nongnu.org; Wed, 10 Jun 2020 12:29:18 -0400 Received: from us-smtp-delivery-1.mimecast.com ([205.139.110.120]:44172 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 1jj3bI-0005Vl-D2 for qemu-devel@nongnu.org; Wed, 10 Jun 2020 12:29:17 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1591806555; 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=sAbKxMQGFPVu4UkAhaHkmv2rOxwrHX6xVrrdaAiD1d8=; b=OIi9AH9otIb/xP/mGX7igyLQ7ZzoFSARfN0v1dASr0xYgh/GSVGLXcwQANi8HOexKqm5VZ Sqzp7KVEtYyquKOy6LWR1vXehZGRvr1OKdEDBdp7SXKPhs3WStj/GuE4x3zRc2GoAS2wP0 OXG+g1n25qJ1ivX5cx8e8OYa9QX+6jI= 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-316-uct5aVxKPD-O_F0rbFZsYw-1; Wed, 10 Jun 2020 12:29:11 -0400 X-MC-Unique: uct5aVxKPD-O_F0rbFZsYw-1 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.phx2.redhat.com [10.5.11.13]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 58824100CD03; Wed, 10 Jun 2020 16:29:10 +0000 (UTC) Received: from [10.3.113.22] (ovpn-113-22.phx2.redhat.com [10.3.113.22]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 8B4291C4; Wed, 10 Jun 2020 16:29:09 +0000 (UTC) Subject: Re: [PATCH 2/2] block: Call attention to truncation of long NBD exports To: Vladimir Sementsov-Ogievskiy , qemu-devel@nongnu.org References: <20200608182638.3256473-1-eblake@redhat.com> <20200608182638.3256473-3-eblake@redhat.com> <5430f8e5-8f28-d703-1b55-136e2296ec72@virtuozzo.com> From: Eric Blake Organization: Red Hat, Inc. Message-ID: <8bce0710-648b-1862-688c-8cee1cab9c8b@redhat.com> Date: Wed, 10 Jun 2020 11:29:08 -0500 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.8.0 MIME-Version: 1.0 In-Reply-To: <5430f8e5-8f28-d703-1b55-136e2296ec72@virtuozzo.com> Content-Language: en-US X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit Received-SPF: pass client-ip=205.139.110.120; envelope-from=eblake@redhat.com; helo=us-smtp-1.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/06/09 23:51:15 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_H4=-0.01, RCVD_IN_MSPIKE_WL=-0.01, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=_AUTOLEARN 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: Kevin Wolf , qemu-block@nongnu.org, qemu-stable@nongnu.org, Max Reitz , ppandit@redhat.com, xuwei@redhat.com Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 6/10/20 4:24 AM, Vladimir Sementsov-Ogievskiy wrote: > 08.06.2020 21:26, Eric Blake wrote: >> Commit 93676c88 relaxed our NBD client code to request export names up >> to the NBD protocol maximum of 4096 bytes without NUL terminator, even >> though the block layer can't store anything longer than 4096 bytes >> including NUL terminator for display to the user.  Since this means >> there are some export names where we have to truncate things, we can >> at least try to make the truncation a bit more obvious for the user. >> Note that in spite of the truncated display name, we can still >> communicate with an NBD server using such a long export name; this was >> deemed nicer than refusing to even connect to such a server (since the >> server may not be under our control, and since determining our actual >> length limits gets tricky when nbd://host:port/export and >> nbd+unix:///export?socket=/path are themselves variable-length >> expansions beyond the export name but count towards the block layer >> name length). >> >> Reported-by: Xueqiang Wei >> Fixes: https://bugzilla.redhat.com/1843684 >> Signed-off-by: Eric Blake > > Reviewed-by: Vladimir Sementsov-Ogievskiy > >> --- >>   block.c     |  7 +++++-- >>   block/nbd.c | 21 +++++++++++++-------- >>   2 files changed, 18 insertions(+), 10 deletions(-) >> >> diff --git a/block.c b/block.c >> index 8416376c9b71..6dbcb7e083ea 100644 >> --- a/block.c >> +++ b/block.c >> @@ -6809,8 +6809,11 @@ void bdrv_refresh_filename(BlockDriverState *bs) >>           pstrcpy(bs->filename, sizeof(bs->filename), >> bs->exact_filename); >>       } else { >>           QString *json = >> qobject_to_json(QOBJECT(bs->full_open_options)); >> -        snprintf(bs->filename, sizeof(bs->filename), "json:%s", >> -                 qstring_get_str(json)); >> +        if (snprintf(bs->filename, sizeof(bs->filename), "json:%s", >> +                     qstring_get_str(json)) >= sizeof(bs->filename)) { >> +            /* Give user a hint if we truncated things. */ >> +            strcpy(bs->filename + sizeof(bs->filename) - 4, "..."); >> +        } > > Is  4096 really enough for json in normal cases? By its very nature, a json string tends be longer than a counterpart URI string representing the same information (when such an explicit name exists) because of the extra characters burned in adding "key":value pairs wrapping the data that was compact in explicit form. But 4k is still quite a lot, and the only cases I've seen where names don't fit in JSON form is where the user was explicitly trying to break things with corner-case testing, rather than what you get with day-to-day use. -- Eric Blake, Principal Software Engineer Red Hat, Inc. +1-919-301-3226 Virtualization: qemu.org | libvirt.org