From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:52005) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1cjRdf-0007zU-L7 for qemu-devel@nongnu.org; Thu, 02 Mar 2017 09:23:28 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1cjRde-0000rO-Kz for qemu-devel@nongnu.org; Thu, 02 Mar 2017 09:23:27 -0500 Date: Thu, 2 Mar 2017 15:23:18 +0100 From: Kevin Wolf Message-ID: <20170302142318.GA5868@noname.redhat.com> References: <20170301081504.23595-1-famz@redhat.com> <20170301094917.GA4799@noname.redhat.com> <20170301123913.GA26744@lemon.lan> <20170301151626.GB4799@noname.redhat.com> <20170301161023.GA17634@lemon.lan> <20170301162221.GD4799@noname.redhat.com> <20170302112110.GA21732@lemon.lan> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170302112110.GA21732@lemon.lan> Subject: Re: [Qemu-devel] [PATCH RFC] block: Tolerate existing writers on read only BdrvChild List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Fam Zheng Cc: qemu-devel@nongnu.org, Max Reitz , qemu-block@nongnu.org Am 02.03.2017 um 12:21 hat Fam Zheng geschrieben: > On Wed, 03/01 17:22, Kevin Wolf wrote: > > Am 01.03.2017 um 17:10 hat Fam Zheng geschrieben: > > > On Wed, 03/01 16:16, Kevin Wolf wrote: > > > > > I'm not sure about this because: 1) this is intrusive from a user PoV, many > > > > > scripts and upper layer tools will stop working; > > > > > > > > Are you sure? I don't expect user scripts or even proper management > > > > tools to use qemu-io on running VMs. I do expect that some users are > > > > using 'convert -s' with running VMs despite our recommendation against > > > > it. > > > > > > > > If they are aware that they're doing something that works only in the > > > > right circumstances, then breaking it isn't nice. But my gut feeling is > > > > that most of them don't know about the implications of accessing a live > > > > image. In this case breaking their use case and making them think about > > > > whether they want to add something like a --force option sounds like a > > > > good thing because they aren't caught by surprise when things go wrong > > > > eventually. > > > > > > Yes, the use case is poor for qcow2, and your points stand there. But image > > > locking will be at the posix level, which has a wider range of users. I cannot > > > draw the same conclusion on raw images as easily. > > > > Well, with raw, I'm even less concerned about breaking the commands > > related to internal snapshots. :-) > > Yes, I'm agree with a --force there. For qemu-img map and qemu-io, personally I > think it's better to keep the default working. qemu-io is a expert mode tool, > whoever using it at all should already know what he's doing, --force doesn't add > much protection for the innocent. Being an expert doesn't protect you from stupid mistakes like forgetting that a VM is still running. --force doesn't prevent you from performing your evil action, but it prevents accidents where you didn't even intend to be evil for a change. I think qemu-io and qemu-img map are tools that only human users should be using while a VM is running, so breaking command line syntax compatibility by requiring a --force option wouldn't hurt too much. Kevin