[libvirt] [PATCH 00/30] storagefile, security: qcow2 data_file support

[Cole Robinson]

Hmm why wasn't I in to/cc list, was that intentional?

On 10/17/19 5:26 AM, Christophe de Dinechin wrote:
> 
> Cole Robinson writes:
> 
>> This series is the first steps to teaching libvirt about qcow2
>> data_file support, aka external data files or qcow2 external metadata.
>>
>> A bit about the feature: it was added in qemu 4.0. It essentially
>> creates a two part image file: a qcow2 layer that just tracks the
>> image metadata, and a separate data file which is stores the VM
> 
> s/is stores/stores/

Indeed, but what's the benefit of correcting grammar in a cover letter
for already applied patches?

> 
>> disk contents. AFAICT the driving use case is to keep a fully coherent
>> raw disk image on disk, and only use qcow2 as an intermediate metadata
>> layer when necessary, for things like incremental backup support.
>>
>> The original qemu patch posting is here:
>> https://lists.gnu.org/archive/html/qemu-devel/2019-02/msg07496.html
>>
>> For testing, you can create a new qcow2+raw data_file image from an
>> existing image, like:
>>
>>     qemu-img convert -O qcow2 \
>>         -o data_file=NEW.raw,data_file_raw=yes
>>         EXISTING.raw NEW.qcow2
> 
> What happens if you try to do that in place, i.e. EXISTING==NEW?
> 

Results in an unbootable image in my testing. I'm guessing it
initializes the raw image first, similar to trying to use 'qemu-img
create' with an existing raw image as data_file

https://bugzilla.redhat.com/show_bug.cgi?id=1688814#c8

- Cole