[anelson]

My company maintains an out-of-tree kernel module for changed block tracking. It requires a full-time Linux driver developer to keep it compiling and working on new kernels.

Our module is GPL FWIW but I doubt it would be accepted into the kernel tree as it is. We need to have a driver developer on staff anyway to support it so it works out okay for us. But if we ever stop maintaining it, it will bitrot quickly and stop working on new kernels.