Support snapshots for btrfs volumes

[mzhaase]

TL;DR

Since btrfs is a supported filesystem for hcloud volumes, it should also be possible to implement PVC snapshots using btrfs snapshots.

Expected behavior

VolumeSnapshot resources should be supported for hcloud volumes for storage classes which define csi.storage.k8s.io/fsType: btrfs

[apricote]

Hello @mzhaase,

in my opinion this is not the responsibility of the csi-driver. In an ideal world you could wrap the csi-driver in some way, where we only handle the block device and the wrapping tool would handle the file system and any file system specific features.

If the API adds support for Snapshots we will too, but we will not add user space snapshots here.

See #285 for a previous topic on this (though with LVM Snapshots instead of btrfs).