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

From: Fam Zheng
Subject: Re: [Qemu-block] [PATCH RFC] block: Tolerate existing writers on read only BdrvChild
Date: Thu, 2 Mar 2017 00:10:23 +0800
User-agent: Mutt/1.7.1 (2016-10-04)

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.

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