gazagnaire.org / ocaml-xen
Xen paravirtual platform and drivers in OCaml
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README.md

nox-xen#

Warning. This is a work-in-progress experimental fork of the MirageOS Xen stack -- mirage-net-xen, mirage-block-xen, shared-memory-ring and mirage-xen. Do not use it in production; use those libraries instead.

The Xen paravirtual platform and drivers for the mirage-eio Eio backend. Most of it is imported from the MirageOS Xen libraries (ISC, (c) the MirageOS authors) and adapted to the Eio backend:

  • Xen.Ring -- the split-ring request/response protocol, from mirage/shared-memory-ring. Xen.Ring.Rpc is I/O-free over Cstruct, so the frontend and backend sides compose in a host loopback and against a real Xen backend domain unchanged.
  • Xen.Net / Xen.Netfront -- the network frontend, from mirage/mirage-net-xen.
  • Xen.Block / Xen.Blkfront -- the block frontend, from mirage/mirage-block-xen.
  • Xen.Grant, Xen.Evtchn, Xen.Clock and Xen.Platform -- grant tables, event channels and the wall clock, from mirage/mirage-xen.

Xen.Xenstore and Xen.Xenbus are the two clean-room modules. Rather than depend on the existing OCaml implementations, they are written from the Xen protocol specifications the house way: the wire framing decoded over the wire codec and the protocol itself a pure state machine, with the ring or socket I/O left to a thin adapter. That structure is the point -- the clients are I/O-free, so they are tested without a live ring and reused unchanged over a host loopback and against a real Xen peer.

Xen.Xenstore is a client for the XenStore key/value protocol a frontend and backend rendezvous over (ring-grant reference, event-channel port, device state): the xs_wire.h message framing over wire and a pure request/reply state machine. The original OCaml XenStore is mirage/ocaml-xenstore by Thomas Gazagnaire and Vincent Hanquez (Citrix; see the OXenstored ICFP 2009 paper), which is LGPL-2.1.

Xen.Xenbus drives the device-connection handshake (the XenbusState enum of io/xenbus.h) the same way -- a pure state machine with a thin adapter -- so the same logic serves a xenstore rendezvous (a normal Xen domU) and a static dom0less one.

Installation#

Install with opam:

$ opam install nox-xen

If opam cannot find the package, it may not yet be released in the public opam-repository. Add the overlay repository, then install it:

$ opam repo add samoht https://tangled.org/gazagnaire.org/opam-overlay.git
$ opam update
$ opam install nox-xen

License#

ISC, matching the upstream MirageOS libraries. See LICENSE.md. The clean-room Xen.Xenstore and Xen.Xenbus modules are ISC, (c) Thomas Gazagnaire.