Libvirt Snapshot Question

[Peter Krempa]

On Thu, Dec 02, 2021 at 16:27:00 +0100, Elias Mobery wrote:
> OK, so I tried both ways. (The VM image is in the read-only squashfs.)
> 
> 1.) Editing VM domain XML:
>     <disk>
> 
>     <transient/>
>     </disk>
> 
> Error:  Internal Error - Could not open
> /var/lib/libvirt/images/vm.snapshot1 : Permission Denied
> 
> I chowned everything to libvirt but no changes. Maybe a read-only conflict?

Yes, the overlay is created in the same path as the original image, just
with a suffix, so if that is a read-only FS it will not work.

I've thought about adding a possibility to specify the location for the
overlay but didn't ever get to implementing it actually.

> 2.) Adding second disk to VM domain XML
> (shortened )
> 
>  <disk>
>     source /var/lib..../images/vm.qcow2
>     target dev=vda
>  </disk>
> 
> 
>  <disk>
>      source /var/lib...../images/vm.qcow2
>      target dev=vdb
>     <transient/>
>  </disk>
> 
> Error: unsupported configuration: cannot create external snapshot for disk
> vdb - collision with disk vdb.

Could you please post the unabbreviated steps? I don't really know
what's going on based on this.

> After googling I found that a lot of people get permission denied errors
> using transient. I will keep looking, really not sure.