services: Rewrite using gexps.

* gnu/services.scm (<service>)[inputs]: Remove.
* gnu/system.scm (links): Remove.
  (etc-directory): Add PASSWD and SHADOW to #:inputs.
  (operating-system-boot-script): Pass ETC to 'dmd-configuration-file'.
  (operating-system-derivation): Remove EXTRAS from the union.
* gnu/system/linux.scm (pam-service->configuration): Rewrite in terms of
  'gexp->derivation'.  Compute the contents on the build side.  Expect
  'arguments' to contain a list of gexps.
  (pam-services->directory): Rewrite in terms of 'gexp->derivation'.
  (unix-pam-service): Change 'arguments' to a list of one gexp.
* gnu/system/shadow.scm (<user-account>)[inputs]: Remove.
  [shell]: Change default value to a gexp.
  (passwd-file): Rewrite in terms of 'gexp->derivation'.  Compute
  contents on the build side.
* gnu/services/base.scm (host-name-service, mingetty-service,
  nscd-service, syslog-service, guix-service): Change 'start' and 'stop'
  to gexps; remove 'inputs' field.
  (guix-build-accounts): Change 'shell' field to a gexp.
* gnu/services/networking.scm (static-networking-service): Change
  'start' and 'stop' to gexps; remove 'inputs' field.
* gnu/services/xorg.scm (slim-service): Likewise.
* gnu/services/dmd.scm (dmd-configuration-file): Expect ETC to be a
  derivation.  Change 'config' to a gexp.  Use 'gexp->file' instead of
  'text-file'.
* doc/guix.texi (Defining Services): Update nscd example with gexps, and
  without 'inputs'.  Add xref to "G-Expressions".

system: Factorize (gnu system).

* gnu/system.scm (operating-system-accounts,
  operating-system-etc-directory): New procedures.
  (operating-system-derivation): Use them.
* gnu/services/base.scm (%base-services): Add 'host-name-service'
  invocation.

Merge branch 'master' into core-updates

Conflicts:
	gnu-system.am

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: dmd: Add SLiM service.

* gnu/system/dmd.scm (xorg-service): Remove.
  (xorg-start-command, slim-service): New procedure.

gnu: dmd: Fix X font directory name in X service.

* gnu/system/dmd.scm (xorg-service)[xserver.conf]: Fix directory name in
  'FontPath' entry for FONT-ADOBE75DPI.

gnu: dmd: Use 'text-file*' when building Xorg's config file.

* gnu/system/dmd.scm (xorg-service)[xserver.conf]: Change to use
  'text-file*' instead of 'text-file'.
  Adjust body accordingly.  Remove now extraneous packages from the
  service's 'inputs' field.

gnu: Add preliminary Xorg service.

* gnu/system/dmd.scm (xorg-service): New procedure.

Merge branch 'master' into core-updates

gnu: Changes references to (gnu packages admin).

* gnu/packages/version-control.scm, gnu/packages/vim.scm,
  gnu/system.scm, gnu/system/dmd.scm, gnu/system/shadow.scm,
  gnu/system/vm.scm: Change references to (gnu packages system) to (gnu
  packages admin).
  This is a followup to commit 4aeea89.

gnu: Add 'inputs' field to <user-account>; make 'shell' a monadic value.

* gnu/system/shadow.scm (<user-account>)[inputs]: New field.
  (passwd-file): Bind the 'shell' field of each account.
* gnu/system/vm.scm (%demo-operating-system): Remove 'shell' field.
* gnu/system/dmd.scm (guix-build-accounts): Store a monadic value in
  'shell'.  Add 'inputs' field.
* gnu/system.scm (operating-system-derivation): Remove 'shell' field for
  'root' account.  Add all the 'user-account-inputs' to EXTRAS.

gnu: dmd: Avoid "already exists" error on startup.

* gnu/system/dmd.scm (dmd-configuration-file)[config]: Remove
  "/var/nix/gcroots/etc-directory" before trying to recreate it.

gnu: Populate /etc upon startup.

* gnu/packages/patches/dmd-getpw.patch: New file.
* gnu-system.am (dist_patch_DATA): Add it.
* gnu/packages/system.scm (dmd): Use it.
* gnu/system/vm.scm (system-qemu-image): Don't explicitly populate /etc;
  don't add ETC to the GC roots.
* gnu/system/dmd.scm (dmd-configuration-file): Add 'etc' parameter.
  [config]: Populate /etc from there.

gnu: dmd: Add 'pam-services' field to <service>.

* gnu/system/dmd.scm (<service>)[pam-services]: New field.
  (mingetty-service): Add #:motd and #:allow-empty-passwords?
  parameters.  Add MOTD to 'inputs' field; add 'pam-services' field.
* gnu/system/vm.scm (system-qemu-image): Aggregate PAM entries from
  SERVICES.

gnu: dmd: Add 'user-accounts' and 'user-groups' fields to <service>.

* gnu/system/shadow.scm (guix-build-accounts): Move to...
* gnu/system/dmd.scm (guix-build-accounts): ... here.
  (<service>)[user-accounts, user-groups]: New fields.
  (guix-service): New #:build-user-id and #:build-accounts parameters.
  Use 'guix-build-accounts' and set the 'user-accounts' and
  'user-groups' fields accordingly.
* gnu/system/vm.scm (system-qemu-image): Remove use of
  'guix-build-accounts'.  Augment ACCOUNTS and GROUPS from what SERVICES
  demand.

gnu: Move /etc/resolv.conf handling to the networking service.

* gnu/system/vm.scm (etc-directory): Remove 'resolv.conf'.
  (system-qemu-image): Use 'static-networking-service' with
  #:name-servers.  Don't populate the image with /etc/resolv.conf.
* gnu/system/dmd.scm (static-networking-service): Add #:name-servers
  parameter.  Use it to populate /etc/resolv.conf.

gnu: dmd: Update start/stop of standard service definitions.

* gnu/system/dmd.scm (mingetty-service): Add 'stop' field.
  (nscd-service): Run with '--foreground'.  Change 'stop' to use
  'make-kill-destructor'.
  (syslog-service): Run with '--no-detach'; change 'stop' similarly.
  (guix-service): Likewise for 'stop'.
  (static-networking-service): Remove 'sleep' call from 'start'.  Change
  'stop' to return #f when networking was actually stopped.

gnu: dmd: Add service documentation.

* gnu/system/dmd.scm (<service>): Add 'documentation' field.
  (host-name-service, mingetty-service, nscd-service, syslog-service,
  static-networking-service): Provide a 'documentation' value.
  (dmd-configuration-file): Use it.

gnu: vm: Rewrite helper functions as monadic functions.

* gnu/system/dmd.scm (host-name-service, nscd-service, mingetty-service,
  syslog-service, guix-service, static-networking-service): Rewrite as
  monadic functions.
  (dmd-configuration-file): Use 'text-file' instead of
  'add-text-to-store'.
* gnu/system/grub.scm (grub-configuration-file): Rewrite as a monadic
  function.
* gnu/system/linux.scm (pam-services->directory): Likewise.
* gnu/system/shadow.scm (group-file, passwd-file, guix-build-accounts):
  Likewise.
* gnu/system/vm.scm (expression->derivation-in-linux-vm, qemu-image,
  union, system-qemu-image): Likewise.

gnu: dmd: Make the 'networking' service slightly more robust.

* gnu/system/dmd.scm (static-networking-service)[start]: Sleep before
  running 'route', to leave time for the interface to come up.
  [stop]: Run "route del -net default".