[libvirt] disk XML for error policy

[Daniel P. Berrange]

On Tue, Mar 16, 2010 at 10:14:26PM -0400, Dave Allan wrote:
> Hi Dan,
> 
> What do you think of this for the disk XML specifying what to do on error:
> 
>     <disk type='file' device='disk'>
>       <source file='/storage/guest_disks/libgdu'/>
>       <target dev='vda' bus='virtio'/>
>       <on_err rerror='stop' werror='stop'/>
>     </disk>

I'm in two minds as to whether we really need separate policies for read 
and write. I know QEMU supports that, but even those who implememted it
told me it was rather redundant & a historical accident because they did
not want to rename the existing 'werror' attribute when they added the
'rerror' bit. So unless someone has a compelling reason for them to be
separate I think we can have a single policy.

If we follow the style of the <on_reboot> <on_poweroff> elements we'd
have something like

  <on_error>stop</on_error>

My only other thought would be to do it as an attribute on the existing
<driver> element in disks, where we have disk format & cache mode already

Regards,
Daniel
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