[$] FFI type mismatches in Rust for Linux

At Kangrejos, Gary Guo wanted to discuss three problems with the way
Rust and C code in the kernel interact: mismatched types, too many type casts,
and the overhead of helper functions. To fix the first two problems, Guo proposed
changing the way the kernel maps C types into Rust types. The last problem was a
bit trickier, but he has a clever workaround for that, based on tricking
the compiler into inlining the helper functions across language boundaries.