[libvirt-users] Immutable backing files

[Peter Krempa]

On Tue, Sep 04, 2018 at 17:32:49 +0200, Gionatan Danti wrote:
> Il 03-09-2018 13:14 Gionatan Danti ha scritto:
> > Hi list,
> > suppose I have an immutable (ie: due to a read-only snapshot) backing
> > file.
> > 
> > After creating an overlay file with "qemu-img create -f qcow2 -o
> > backing_file=/path/to/immutable/file.img current.qcow2", libvirt
> > refuse to start the virtual machine and exits with an error stating
> > "Could not open backing file /path/to/immutable/file.img: Permission
> > denied".
> > 
> > From my understanding, libvirtd is trying to change the
> > owner/permissions/selinux context of the backing file but, being it
> > immutable, fails to start the VM. Is that the expected behavior?
> > 
> > Thanks.
> 
> Hi all, any suggestion on the matter?

You forgot to specify the format of the backing file into the overlay
file (qemu-img option -F). Libvirt treats any unspecified format as raw
since it's not secure to do probing of the format.


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