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.

gnu: vm: Add /etc/shadow in the QEMU image.

* gnu/system/vm.scm (qemu-image): Add 'populate' keyword parameter and
  honor it; make it an input.
  (/etc/shadow): New procedure.
  (example2): Call it; build 'populate' script, and pass it to
  'qemu-image'.

gnu: vm: Remove unused 'qemu-image' argument.

* gnu/system/vm.scm (qemu-image): Remove 'boot-expression' parameter,
  superseded by 'linux-arguments'.

gnu: vm: First stab at building a populated QEMU image.

* gnu/packages/linux-initrd.scm (gnu-system-initrd): New variable.
* gnu/system/vm.scm (qemu-image): Add #:linux-arguments parameter.
  [input->name+derivation]: Add case for 'store-path?' items.
  Remove LOADER from `inputs'.

gnu: vm: 'qemu-image' populates /dev on the target root file system.

* gnu/system/vm.scm (qemu-image): Use (guix build linux-initrd).  Remove
  'mknod' calls; use 'make-essential-device-nodes' to populate /dev on
  the target image.
* gnu/packages/linux-initrd.scm (qemu-initrd): When /root/dev exists,
  don't call 'make-essential-device-nodes'.

gnu: vm: `qemu-image' can copy store closures into the target image.

* gnu/system/vm.scm (qemu-image): Add #:inputs-to-copy and
  #:boot-expression parameters.  Honor them.  Append INPUTS-TO-COPY to
  the #:inputs argument for `expression->derivation-in-linux-vm'.
  (example2): Add #:boot-expression and #:inputs-to-copy arguments.

gnu: `expression->derivation-in-linux-vm' accepts files as inputs.

* gnu/system/vm.scm (expression->derivation-in-linux-vm): Accept items
  in INPUTS that refer to a file instead of a package.

gnu: `expression->derivation-in-linux-vm' export references graphs.

* gnu/system/vm.scm (expression->derivation-in-linux-vm): Add
  #:reference-graphs parameter.  Honor it.  Delete duplicates in
  #:modules argument.

vm: Use more keyword parameters for `expression->derivation-in-linux-vm'.

* gnu/system/vm.scm (expression->derivation-in-linux-vm): Turn `system'
  and `inputs' into keyword parameters.
  (qemu-image, example1): Adjust accordingly.