Block-device snapshots with blksnap

As the DM subsystem maintainer I don't recall you ever directly or indirectly contacting me (famous last words). But I've _never_ been opposed to devising a way to make all block devices capable of being remapped without first needing to have created the DM device at the dawn of time.

The need for such a capability is quite niche... but I don't dispute that those who would like it exist (and might jump to false accusations about others :/ ).

The coding of such an advance just hasn't been a priority _for me or my broader team within Red Hat_. That doesn't mean "DM folks" reject the idea. It means others need to do the work. Implementing it in terms of yet another way to remap IO (blkfilter) speaks to inherent lack of understanding on how to make a general purpose advance that doesn't further splinter the block core's capabilities.