vm: Move image creation to (guix build vm); split into several procedures.

* guix/build/vm.scm (read-reference-graph, initialize-partition-table,
  install-grub, populate-store, evaluate-populate-directive,
  reset-timestamps, initialize-hard-disk): New procedures.
* gnu/system/vm.scm (qemu-image): Change 'builder' to a call to
  'initialize-hard-disk'.

vm: 'expression->derivation-in-linux-vm' can import modules in the VM.

* gnu/system/vm.scm (%imported-modules): New procedure.
  (expression->derivation-in-linux-vm): Add #:imported-modules
  parameter; remove #:modules.  Add LOADER, and change BUILDER to load
  it.
  (qemu-image): Remove useless #:modules argument.

vm: Strip import list.

* gnu/system/vm.scm: Strip #:select for (gnu packages base).

vm: Factorize input conversion.

* gnu/system/vm.scm (input->name+output): New procedure.
  (expression->derivation-in-linux-vm): Use it for 'input-alist'.
  (qemu-image)[input->name+derivation]: Remove.  Use
  'input->name+output' instead.

vm: Add (guix build vm) module.

* guix/build/vm.scm: New file.
* Makefile.am (MODULES): Add it.
* gnu/system/vm.scm (expression->derivation-in-linux-vm): Use it.

vm: Use QEMU's para-virtualized file system support for all VMs.

* gnu/system/vm.scm (system-qemu-image/shared-store-script): Change
  #:qemu to default to QEMU.  Change INITRD to use a 9p mount for the
  store.  Change command-line to use -virtfs.

gnu: guix: Upgrade to 0.6.

* gnu/packages/package-management.scm (guix): Upgrade to 0.6.
* gnu/services/dmd.scm (dmd-configuration-file): Change /var/nix to
  /var/guix.
* gnu/system/vm.scm (operating-system-default-contents): Likewise.

vm: Add #:memory-size parameter for 'expression->derivation-in-linux-vm'.

* gnu/system/vm.scm (expression->derivation-in-linux-vm): Add
  #:memory-size parameter, defaulting to 256 (QEMU defaults to 128.)

vm: 'expression->derivation-in-linux-vm' uses QEMU virtfs/9p.

* gnu/system/vm.scm (expression->derivation-in-linux-vm): Change #:qemu
  to default to QEMU-HEADLESS.  Use "-net nic,model=virtio".  Remove
  "-net user,smb=..." and add "-virtfs" options.  Change default initrd
  to include two 9p mounts.

Merge branch 'master' into core-updates

More /gnu/store replacements.

* gnu/packages/gcc.scm (gcc-4.7): Change /nix/store in comment.
* gnu/system/vm.scm (operating-system-default-contents):
  Use (%store-prefix) instead of "/nix/store".
* guix/derivations.scm (derivation-path->output-path,
  derivation-path->output-paths): Change to /gnu/store in docstring.

Merge branch 'master' into core-updates

gnu: linux-initrd: Make the pseudo-tty device nodes.

* guix/build/linux-initrd.scm (make-essential-device-nodes): Create
  /dev/ptmx and /dev/pts.
* gnu/system/vm.scm (qemu-image): Umount /fs/dev/pts before /fs.

Merge branch 'master' into core-updates

Conflicts:
	gnu-system.am

gnu: vm: Remove '%demo-operating-system'.

* gnu/system/vm.scm (%demo-operating-system): Remove.
  (system-qemu-image, system-qemu-image/shared-store,
  system-qemu-image/shared-store-script): Adjust accordingly.

gnu: Introduce the (gnu services ...) modules.

* gnu/system/dmd.scm: Remove file.  Move contents to...
* gnu/services.scm, gnu/services/base.scm, gnu/services/dmd.scm,
  gnu/services/networking.scm, gnu/services/xorg.scm: ... here.  New
  files.
* gnu/system.scm, gnu/system/vm.scm: Adjust accordingly.
* guix/scripts/system.scm (%user-module): Likewise.
* doc/guix.texi (Using the Configuration System): Likewise.
  (Defining Services): Likewise.

gnu: Move root's home directory to /root.

* gnu/system.scm (operating-system-derivation): Change root's
  'home-directory' to "/root".
* gnu/system/vm.scm (operating-system-default-contents): Add /root.

gnu: vm: Create all the user directories.

* gnu/system/vm.scm (operating-system-default-contents)[user-directories]:
  New procedure.  Use it to create each user's home and GC root
  directories.

gnu: vm: Add /run/current-system and /bin/sh.

* gnu/system/vm.scm (operating-system-default-contents): Populate
  /run/current-system and create /bin/sh.
* gnu/system.scm (operating-system-profile-derivation,
  operating-system-profile-directory): New procedures.
  (operating-system-derivation): Use it.

gnu: vm: Add support for running a VM that shares its store with the host.

* gnu/system/vm.scm (qemu-image): Check whether GUIX is #f.
  (operating-system-build-gid, operating-system-default-contents): New
  procedures.
  (system-qemu-image): Use 'operating-system-build-gid'.
  (system-qemu-image/shared-store,
  system-qemu-image/shared-store-script): New procedures.
* gnu/system.scm: Add missing exports.