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/
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?
The goal of this series is to teach libvirt enough about this case so that we can correctly relabel the data_file on VM startup/shutdown. The main functional changes are
* Teach storagefile how to parse out data_file from the qcow2 header * Store the raw string as virStorageSource->externalDataStoreRaw * Track that as its out virStorageSource in externalDataStore * dac/selinux relabel externalDataStore as needed
-- Cheers, Christophe de Dinechin (IRC c3d)