[avsm]

No, the idea is a bit broader. By structuring your application in a modular set of libraries, you can break up the "ambient dependencies" (e.g. the monolithic kernel) into what your application actually needs.

Once that's done, the Xen backend is just a matter of filling in the missing kernel components with OCaml libraries (or, in the case of OSv, with C libraries, or in HalVM's, Haskell libraries).

In the case of MirageOS though, we're using this fine-grained dependency control to implement other backends too. For instance, compiling the same source code to run as a FreeBSD kernel module or as a JavaScript library. There's already a Unix backend, so nothing special needs to happen to run it under Docker.