This is similar to `Box::into_raw` in Rust `std`. It destructs the RAII struct into a raw pointer. After that it's pretty much expected that you are responsible for cleanup.
Obviously forcing callers to free means adding lints and docs. Returning borrows leaves the likelihood of entering into explicit lifetimes hell and such in calling code.
A functional interface like (paraphrasing)
// pub fn apply_op(&mut self, FnMut(&mut T, &bindings::dma_addr_t... ))
Just like `Box::into_raw`, this method shouldn't be used in pure Rust code. It's only available for C FFI.