Update on VM support

[Ludovic Courtès]

Hello!

A summary of the recent changes in (gnu system vm) & co.:

  • This module now uses QEMU’s 9p file system support (-virtfs) to
    share files with the host (previously it used Samba to expose a CIFS
    share to the guest, because that’s what QEMU made easy to support
    historically, but it was much slower, less flexible, and required a
    custom patch to share more than one directory.)

  • The build-side part of the code has been moved to (guix build vm)
    and modularized.  It is much more readable and flexible now.  :-)

  • When building a VM that shares its store with the host, as with
    ‘guix system vm’, unionfs-fuse is used to get a writable file
    system.  That file system is the union of the real root provided by
    the image, which is read-only, and a writable tmpfs.

That improves development and testing with ‘guix system vm’.  Some of it
will also be reusable for the installation CD/USB key image.

Ludo’.