[Bf-committers] Reference counting, deleting data and fake users

[Lukas Tönne]

The technical difficulty with explicit deletion of data blocks is that
we currently have no way to inform all users of a data block when it
is deleted. From a coders perspective it is currently quite simple: as
long as you hold a link, that link is always valid. This also is
related to the dependency graph, at least a better depgraph would be a
consistent solution: a link to another data block is a very basic
dependency on that data block. Any user can then be updated before the
actual deletion, without any specialized system just for this purpose.