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Mon, 9 Mar 2020 15:36:35 +0000 (UTC) Received: from redhat.com (ovpn-112-61.ams2.redhat.com [10.36.112.61]) by smtp.corp.redhat.com (Postfix) with ESMTPS id E754E1BC6D; Mon, 9 Mar 2020 15:36:27 +0000 (UTC) Date: Mon, 9 Mar 2020 15:36:24 +0000 From: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= To: Kevin Wolf Subject: Re: [PATCH v3 1/4] block: Add trivial backing_fmt support to qcow, sheepdog, vmdk Message-ID: <20200309153624.GK3033513@redhat.com> References: <20200306225121.3199279-1-eblake@redhat.com> <20200306225121.3199279-2-eblake@redhat.com> <20200309152112.GC6478@linux.fritz.box> MIME-Version: 1.0 In-Reply-To: <20200309152112.GC6478@linux.fritz.box> User-Agent: Mutt/1.13.3 (2020-01-12) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 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: 207.211.31.81 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: , Reply-To: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= Cc: Fam Zheng , pkrempa@redhat.com, "open list:Sheepdog" , qemu-block@nongnu.org, libvir-list@redhat.com, Michael Tokarev , qemu-devel@nongnu.org, mreitz@redhat.com, "open list:Trivial patches" , Liu Yuan , Laurent Vivier Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Mon, Mar 09, 2020 at 04:21:12PM +0100, Kevin Wolf wrote: > Am 06.03.2020 um 23:51 hat Eric Blake geschrieben: > > For qcow2 and qed, we want to encourage the use of -F always, as these > > formats can suffer from data corruption or security holes if backing > > format is probed. But for other formats, the backing format cannot be > > recorded. Making the user decide on a per-format basis whether to > > supply a backing format string is awkward, better is to just blindly > > accept a backing format argument even if it is ignored by the > > contraints of the format at hand. > >=20 > > Signed-off-by: Eric Blake >=20 > I'm not sure if I agree with this reasoning. Accepting and silently > ignoring -F could give users a false sense of security. If I specify a > -F raw and QEMU later probes qcow2, that would be very surprising. And if the user specifies "-F raw" and we probe qcow2, and the user does not realize this, they can become silently reliant on always probing qcow2. If we then honour the "-F raw" option in a later QEMU release, we'll break the behaviour they've relied on. IMHO, we must not accept "-F fmt" unless we're in a position to honour it. Regards, Daniel --=20 |: https://berrange.com -o- https://www.flickr.com/photos/dberrange= :| |: https://libvirt.org -o- https://fstop138.berrange.com= :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange= :|