[$] How to write Rust in the kernel: part 3

The interfaces between C and Rust in the kernel have grown over time; any
non-trivial Rust driver will use a number of these. Tasks like allocating memory,
dealing with immovable structures, and interacting with locks are necessary for
handling most devices. There are also many subsystem-specific bindings, but the
focus this time will be on an overview of the bindings that all kernel Rust code
can be expected to use.