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Re: [Qemu-block] [PATCH RFC] block: Tolerate existing writers on read on

From: Kevin Wolf
Subject: Re: [Qemu-block] [PATCH RFC] block: Tolerate existing writers on read only BdrvChild
Date: Wed, 1 Mar 2017 17:22:21 +0100
User-agent: Mutt/1.5.21 (2010-09-15)

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. :-)


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