[libvirt] "virsh edit" failed to take effect on KVM

[Daniel P. Berrange]

On Thu, May 09, 2013 at 11:49:05AM +0000, Gonglei (Arei) wrote:
> Hi all,
>    we use the command "virsh edit"  to modify the VM configuration information online on KVM Platform(libvirt-1.0.0 and qemu-1.4), 
> but it does not take effect after reboot. However, it works fine on Xen Platform.
>   
>    for an example,a VM is running with the following configuration information:
> 	   ...
> 	   <os>
> 		<type arch='x86_64'>hvm</type>
> 		<boot dev='hd'/>
> 		<bootmenu enable='yes'/>
> 	  </os>
> 	  ...
>    use command "virsh edit " to modify it:
> 	   ...
> 	   <os>
> 		<type arch='x86_64'>hvm</type>
> 		<boot dev='cdrom'/>
> 		<bootmenu enable='yes'/>
> 	  </os>
> 	  ...
> With the changing, the VM is expected to start from cdrom, when execute the command "virsh reboot".
> But the fact is that the modify does not take effect, the VM is still start from hd. 

"virsh edit" changes the persistent configuration of a guest, and as such this
has no effect on the runtime state of the guest. The changes will only take
effect at the next cold boot. 'virsh reboot' does a warm boot, hence won't see
the changes.

> Well, it will take effect if I use command "virsh shutdown" and "virsh start" instesad of "virsh reboot".
> We are wondering if there have any other ways to take the online modify effect. 
> What is the next step going on with the command "virsh edit" on KVM Platform? Any ideas? 

AFAIK, there is no way to programatically change the BIOS boot order for
a running QEMU process.

Daniel
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