Hi Guix, I believe that this is a feature request. I would like to create a Guix qcow2 image to run as a VM. Additionally, I would like the root file system to be btrfs. Therefore, I created an operating system definition with the following file-systems: ``` (file-systems (cons (file-system (mount-point "/") (device "/dev/vda1") (type "btrfs") (flags '(no-atime)) (options "compress=zstd")) %base-file-systems)) ``` I then ran `guix system vm-image --image-size=10G --volatile config.scm`. That successfully created a qcow2 image, but the root file system was ext4 instead of btrfs. Ideally, I would get an image with a btrfs filesystem. I expect supporting all combinations of filesystems and mapped devices might be challenging for the image creation process, but some more options might be interesting. At the very least, I think a warning or error when the requested configuration is not supported would be appropriate. What do you think about this feature? Best, Jack