[Qemu-devel] "virsh edit" failed to take effect on KVM

[Qemu-devel] "virsh edit" failed to take effect on KVM

[Gonglei (Arei)]

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. 
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? 

Thanks!

-Gonglei

Re: [Qemu-devel] "virsh edit" failed to take effect on KVM

[Laszlo Ersek]

On 05/09/13 13:42, 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. 
> 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? 

Under Xen, "xm reboot" (or, more likely, "xl reboot" recently), which is
what I expect "virsh reboot" to translate to, always creates a brand new
domain. Therefore domain config changes take effect.

Under KVM the same VM instance continues to run, it just goes through an
emulated reset.

Laszlo

Re: [Qemu-devel] "virsh edit" failed to take effect on KVM

[Eric Blake]

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On 05/09/2013 05:42 AM, 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.

This sort of question belongs best on libvirt-users@redhat.com
(libvirt-list-request is not the right list address, and your question
isn't quite relevant to qemu-devel).

> With the changing, the VM is expected to start from cdrom, when execute the command "virsh reboot".

'virsh reboot' triggers a software reboot (reusing the same existing
qemu process); but 'virsh edit' only affects what will take place on a
hard boot (creation of a new qemu process).

> But the fact is that the modify does not take effect, the VM is still start from hd. 
> Well, it will take effect if I use command "virsh shutdown" and "virsh start" instesad of "virsh reboot".

Correct, because that sequence spawns a new qemu process.

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org


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