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

[Fam Zheng <famz@redhat.com>]

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.