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=-5.1 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SIGNED_OFF_BY,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 0795FC17441 for ; Tue, 12 Nov 2019 16:04:06 +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 C9C6C20679 for ; Tue, 12 Nov 2019 16:04:05 +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="JtLxWNHU" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org C9C6C20679 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]:37104 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1iUYeC-0003Ua-TZ for qemu-devel@archiver.kernel.org; Tue, 12 Nov 2019 11:04:04 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]:49967) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1iUYdG-0002hH-QZ for qemu-devel@nongnu.org; Tue, 12 Nov 2019 11:03:07 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1iUYdE-0006B5-5h for qemu-devel@nongnu.org; Tue, 12 Nov 2019 11:03:06 -0500 Received: from us-smtp-1.mimecast.com ([205.139.110.61]:39121 helo=us-smtp-delivery-1.mimecast.com) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1iUYdD-00069n-CK for qemu-devel@nongnu.org; Tue, 12 Nov 2019 11:03:04 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1573574582; 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=j+b7McQt0TwaHOoMwGjoe08ORfp22kEQAN/32AGZ6qo=; b=JtLxWNHULNp1ixVjK8khYf/T4dRUd0F0XhTKQambfa3YYCMn/qKJeP1RFMt+Rs+LNGEz1G vMYShuP+zXz3lUqJKI127EPD5PHMtf9RdFkG04VV3nqjScIYHu6V8KsJ6++XKlCsh22KE4 h/TQyH45RVx0+iIiDmIDjkeGEieNuPE= 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-297-o8HPmG4GMAazvspV6vTEfg-1; Tue, 12 Nov 2019 11:01:15 -0500 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.phx2.redhat.com [10.5.11.16]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id CC3E6107ACC8; Tue, 12 Nov 2019 16:01:14 +0000 (UTC) Received: from angien.pipo.sk (unknown [10.43.2.48]) by smtp.corp.redhat.com (Postfix) with ESMTPS id B5D9118213; Tue, 12 Nov 2019 16:01:12 +0000 (UTC) Date: Tue, 12 Nov 2019 17:01:09 +0100 From: Peter Krempa To: Kevin Wolf Subject: Re: [PATCH 1/2] block: Remove 'backing': null from bs->{explicit_,}options Message-ID: <20191112160109.GB163480@angien.pipo.sk> References: <20191108085312.27049-1-kwolf@redhat.com> <20191108085312.27049-2-kwolf@redhat.com> MIME-Version: 1.0 In-Reply-To: <20191108085312.27049-2-kwolf@redhat.com> X-PGP-Key-ID: 0xD018682B X-PGP-Key-Fingerprint: D294 FF38 A6A2 BF40 6C75 5DEF 36EC 16AC D018 682B User-Agent: Mutt/1.12.1 (2019-06-15) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 X-MC-Unique: o8HPmG4GMAazvspV6vTEfg-1 X-Mimecast-Spam-Score: 0 Content-Type: text/plain; charset=WINDOWS-1252 Content-Transfer-Encoding: quoted-printable Content-Disposition: inline X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] [fuzzy] X-Received-From: 205.139.110.61 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, qemu-block@nongnu.org, mreitz@redhat.com Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Fri, Nov 08, 2019 at 09:53:11 +0100, Kevin Wolf wrote: > bs->options and bs->explicit_options shouldn't contain any options for > child nodes. bdrv_open_inherited() takes care to remove any options that > match a child name after opening the image and the same is done when > reopening. >=20 > However, we miss the case of 'backing': null, which is a child option, > but results in no child being created. This means that a 'backing': null > remains in bs->options and bs->explicit_options. >=20 > A typical use for 'backing': null is in live snapshots: blockdev-add for > the qcow2 overlay makes sure not to open the backing file (because it is Note that we also use '"backing": null' as a terminator for the last image in the chain if the user configures the chain manually. This is kind-of a protection from opening the backing file from the header if it was misconfigured somehow. I think this functionality should be kept despite probably not making practical sense. In my testing this scenario worked properly. > already opened and blockdev-snapshot will attach it). After doing a > blockdev-snapshot, bs->options and bs->explicit_options become > inconsistent with the actual state (bs has a backing file now, but the > options still say null). On the next occasion that the image is > reopened, e.g. switching it from read-write to read-only when another > snapshot is taken, the option will take effect again and the node > incorrectly loses its backing file. >=20 > Fix bdrv_open_inherited() to remove the 'backing' option from > bs->options and bs->explicit_options even for the case where it > specifies that no backing file is wanted. >=20 > Reported-by: Peter Krempa > Signed-off-by: Kevin Wolf The fix looks sane-enough to me and works as expected, but since I'm not familiar enough with this code I'm comfortable only with a: Tested-by: Peter Krempa > --- > block.c | 2 ++ > 1 file changed, 2 insertions(+)