gnu: vm: Register the profile as a GC root.

* gnu/system/vm.scm (system-qemu-image): Register PROFILE as a GC root.

gnu: vm: Add 'host-name' service.

* gnu/system/dmd.scm (host-name-service): New procedure.
  (mingetty-service): Require the 'host-name' service.
* gnu/system/vm.scm (system-qemu-image): Add the 'host-name' service.
  Set PS1 in /etc/bashrc to something sensible.

gnu: vm: Add /etc/issue and a motd.

* gnu/system/vm.scm (system-qemu-image): Build a 'motd' and an 'issue'
  file.  Pass 'unix-pam-service' that motd.  Have /etc/issue point to
  the 'issue' file.

gnu: vm: Change #:populate to a list of directives.

* gnu/system/vm.scm (qemu-image): Change 'populate' parameter to be a
  list of directives.
  (system-qemu-image): Adjust accordingly.

gnu: vm: Add more ttys.

* gnu/system/vm.scm (system-qemu-image): Add more ttys.

gnu: vm: Change GRUB label.

* gnu/system/vm.scm (system-qemu-image): Change GRUB label.

gnu: vm: Make a union of the visible packages; add /etc/profile.

* gnu/system/vm.scm (qemu-image): Add Guix as an input when
  INITIALIZE-STORE?.
  (union): New procedure.
  (system-qemu-image): Use it.  Build /etc/profile.  Pass PROFILE among
  #:inputs-to-copy instead of listing all the individual profiles.
  Remove explicit 'build-derivations' call.

gnu: vm: Support derivation objects as inputs.

* gnu/system/vm.scm (expression->derivation-in-linux-vm)[input-alist]:
  Add case for derivation? objects.
  Same for #:inputs values.
  (qemu-image)[input->name+derivation]: Likewise.

gnu: vm: Add a service for the Guix daemon.

* gnu/system/dmd.scm (guix-service): New procedure.
* gnu/system/vm.scm (system-qemu-image): Use it.

gnu: vm: Initialize the image's store.

* gnu/system/vm.scm (qemu-image): Add 'initialize-store?' keyword
  parameter.  Use 'guix-register' when INITIALIZE-STORE? is true.
  (system-qemu-image): Pass #:initialize-store? #t.

gnu: QEMU images boots into dmd.

* gnu/system/dmd.scm: New file.
* gnu/system/vm.scm (system-qemu-image): Define dmd services.
  [populate]: Make var/log and etc/group.
  [boot]: Execute dmd directly.
  Add dmd and etc-group as inputs; add the inputs of dmd services.
* gnu-system.am (GNU_SYSTEM_MODULES): Add gnu/system/dmd.scm.

derivations: 'derivation' and related procedures return a single value.

* guix/derivations.scm (derivation->output-path,
  derivation->output-paths): New procedures.
  (derivation-path->output-path): Use 'derivation->output-path'.
  (derivation-path->output-paths): Use 'derivation->output-paths'.
  (derivation): Accept 'derivation?' objects as inputs.  Return a single
  value.
  (build-derivations): New procedure.
  (compiled-modules): Use 'derivation->output-paths'.
  (build-expression->derivation)[source-path]: Add case for when the
  input matches 'derivation?'.
  [prologue]: Accept 'derivation?' objects in INPUTS.
  [mod-dir, go-dir]: Use 'derivation->output-path'.
* guix/download.scm (url-fetch): Adjust to the single-value return.
* guix/packages.scm (package-output): Use 'derivation->output-path'.
* guix/scripts/build.scm (guix-build): When the argument is
  'derivation-path?', pass it through 'read-derivation'.
  Use 'derivation-file-name' to print out the .drv file names, and to
  register them.  Use 'derivation->output-path' instead of
  'derivation-path->output-path'.
* guix/scripts/package.scm (roll-back): Adjust to the single-value
  return.
  (guix-package): Use 'derivation->output-path'.
* guix/ui.scm (show-what-to-build): Adjust to deal with 'derivation?'
  objects instead of .drv file names.
* gnu/system/grub.scm (grub-configuration-file): Use
  'derivation->output-path' instead of 'derivation-path->output-path'.
* gnu/system/vm.scm (qemu-image, system-qemu-image): Likewise.
* tests/builders.scm, tests/derivations.scm, tests/packages.scm,
  tests/store.scm, tests/union.scm: Adjust to the new calling
  convention.
* doc/guix.texi (Defining Packages, The Store, Derivations): Adjust
  accordingly.

gnu: Move helper code to (gnu system …) modules.

* gnu/packages/grub.scm (<menu-entry>, grub-configuration-file): Move
  to...
* gnu/system/grub.scm: ... here.  New file.
* gnu/packages/linux.scm (<pam-service>, <pam-entry>,
  pam-service->configuration, pam-service->directory,
  %pam-other-services, unix-pam-service): Move to...
* gnu/system/linux.scm: ... here.  New file.
* gnu/system/vm.scm (passwd-file): Move to...
* gnu/system/shadow.scm: ... here.  New file.
* gnu-system.am (GNU_SYSTEM_MODULES): Add
  gnu/system/{grub,linux,shadow}.scm.

gnu: vm: Remove potluck hacks.

* gnu/system/vm.scm (example1): Remove.
  (example2): Rename to...
  (system-qemu-image): ... this.  Add 'store' parameter, and remove call
  to 'open-connection'.

gnu: vm: Setup PAM.

* gnu/system/vm.scm (example2): Use 'pam-services->directory'.  Change
  POPULATE to create /etc/pam.d, /etc/login.defs, and /var/run.  Change
  BOOT to spawn syslogd; boot to Bash.  Add inputs.

gnu: vm: Create shadow files with the right format.

* gnu/system/vm.scm (passwd-file): When SHADOW? is true, use the right
  shadow(5) format.  Always add a trailing newline.

gnu: vm: Copy /etc/shadow to the guest.

* gnu/system/vm.scm (example2): Add SHADOW to #:inputs-to-copy.

gnu: vm: Create valid /etc/shadow and /etc/passwd.

* gnu/system/vm.scm (/etc/passwd): Rename to...
  (passwd-file): ... this. Add 'shadow?' keyword parameter.  Change
  format of ACCOUNTS, and fix CONTENTS.
  (example2): Adjust accordingly.  Create both /etc/shadow and
  /etc/passwd, the latter being used by getpwnam(3) & co. when nscd is
  not running.

gnu: vm: Clear timestamps on the imported files, like in the store.

* gnu/system/vm.scm (qemu-image): Clear timestamps on the copied files.

gnu: grub: Add support for building configuration files.

* gnu/packages/grub.scm (<menu-entry>): New record type.
  (grub-configuration-file): New procedure.
* gnu/system/vm.scm (qemu-image): Remove parameters 'linux',
  'linux-arguments', and 'initrd'.  Add 'grub-configuration' parameter.
  Honor them, and remove grub.cfg generation code accordingly.
  (example2): Use `grub-configuration-file', and adjust accordingly.