system: Add (guix build install) module.

* guix/build/vm.scm (install-grub, evaluate-populate-directive,
  reset-timestamps, register-closure): Move to...
* guix/build/install.scm: ... here.  New file.
* Makefile.am (MODULES): Add it.
* gnu/system/vm.scm (expression->derivation-in-linux-vm): Add (guix
  build install) to #:modules.

vm: Support initialization of the store DB when the store is shared.

* gnu/system/vm.scm (qemu-image): Rename #:inputs-to-copy to #:inputs,
  and #:initialize-store? to #:register-closures?.  Add #:copy-inputs?.
  Adjust build gexp accordingly.
  (system-qemu-image): Remove #:initialize-store? argument and add
  #:copy-inputs?.
  (system-qemu-image/shared-store): Add #:inputs, #:register-closures?,
  and #:copy-inputs? arguments.
* guix/build/vm.scm (register-closure): New procedure.
  (MS_BIND): New variable.
  (initialize-hard-disk): Rename #:initialize-store? to
  #:register-closures?, #:closures-to-copy to #:closures, and add
  #:copy-closures?.
  Add 'target-directory' and 'target-store' variables.
  Call 'populate-store' only when COPY-CLOSURES?.
  Bind-mount the store to TARGET-STORE when REGISTER-CLOSURES? and not
  COPY-CLOSURES?.  Add call to 'register-closure'.

vm: Keep acceptable file systems from the original OS.

* gnu/system/vm.scm (virtualized-operating-system): Instead of
  completely overriding 'file-systems', use 'remove' to filter out some
  of those declared in OS.
  (system-qemu-image): Likewise.

vm: Pass '-serial stdio' in the run-vm.sh.

* gnu/system/vm.scm (system-qemu-image/shared-store-script): Add
  '-serial stdio'.

system: Move skeleton code to (gnu system shadow).

* gnu/system.scm (default-skeletons, skeleton-directory): Move to...
* gnu/system/shadow.scm: ... here.

system: Make accounts and groups at activation time.

* gnu/services/base.scm (guix-build-accounts): Remove #:gid parameter;
  add #:group.  Remove 'password' and 'gid' fields in 'user-account'
  form, and add 'group'.
  (guix-service): Remove #:build-user-gid parameter.  Remove 'id' field
  in 'user-group' form.
* gnu/system.scm (etc-directory): Remove #:groups and #:accounts.  No
  longer produce files "passwd", "shadow", and "group".  Adjust caller
  accordingly.
  (%root-account): New variable.
  (operating-system-accounts): Add 'users' variable.  Add %ROOT-ACCOUNT
  only of 'operating-system-users' doesn't already contain a root
  account.
  (user-group->gexp, user-account->gexp): New procedures.
  (operating-system-boot-script): Add calls to 'setenv' and
  'activate-users+groups' in gexp.
* gnu/system/linux.scm (base-pam-services): Add PAM services for
  "user{add,del,mode}" and "group{add,del,mod}".
* gnu/system/shadow.scm (<user-account>)[gid]: Rename to...
  [group]: ... this.
  [supplementary-groups]: New field.
  [uid, password]: Default to #f.
  (<user-group>)[id]: Default to #f.
  (group-file, passwd-file): Remove.
* gnu/system/vm.scm (operating-system-default-contents)[user-directories]:
  Remove.  Add "/home" to the directives.
* guix/build/activation.scm (add-group, add-user,
  activate-users+groups): New procedures.

vm: Fix recently-introduced regression in 'operating-system-services' use.

* gnu/system/vm.scm (operating-system-build-gid): Adjust to new return
  type of 'operating-system-services' introduced in 217a5b8.

linux-initrd: Check the root and other early file systems.

* gnu/system.scm (operating-system-derivation)[boot-file-systems]: Keep "/".
* gnu/system/linux-initrd.scm (file-system->spec): Keep the 'check?'
  flag.
  (qemu-initrd)[helper-packages]: New variable.  Pass it as #:to-copy.
  <gexp>: Add 'set-path-environment-variable' call.  Remove #:unionfs
  argument for 'boot-system'.
* gnu/system/vm.scm (%linux-vm-file-systems): Add 'check?' field/
  (virtualized-operating-system): Likewise for the "9p" file system.
* guix/build/linux-initrd.scm (mount-root-file-system): Change #:unionfs
  default.  Call 'check-file-system' before mounting ROOT, when
  VOLATILE-ROOT? is false.
  (check-file-system): New procedure.
  (mount-file-system): Honor 'check?' element in list; add
  'check-file-system' call.
  (boot-system): Remove #:root-fs-type and #:unionfs parameters.
  [root-mount-point?, root-fs-type]: New variables.
  Call 'mount-file-system' on all MOUNTS but "/".

vm: Provide a root partition for the freestanding VM image.

Fixes a regression introduced in 83bcd0b.

* gnu/system/vm.scm (system-qemu-image): Override the 'file-systems'
  field of OS.  Add #:file-system-type parameter and honor it.

vm: Make root file system type a parameter, and default to ext4.

* gnu/system/vm.scm (qemu-image): Add #:file-system-type parameter.
  Pass it to 'initialize-hard-disk'.
* guix/build/linux-initrd.scm (mount-root-file-system): Always honor
  TYPE.
  (boot-system): Change #:root-fs-type to default to "ext4".  Update
  docstring.
* guix/build/vm.scm (initialize-hard-disk): Remove #:mkfs parameter; add
  #:file-system-type.  Adjust 'mkfs' invocation and 'mount' call to
  honor #:file-system-type.

system: Add first-class file system declarations.

* gnu/system.scm (<operating-system>)[initrd]: Default to
  'qemu-initrd'.
  (<file-system>): New record type.
  (operating-system-root-file-system): New procedure.
  (operating-system-derivation): Take the device name for GRUB from
  'operating-system-root-file-system'.  Pass the
  'operating-system-initrd' procedure the list of boot file systems.
* gnu/system/linux-initrd.scm (file-system->spec): New procedure.
  (qemu-initrd): Add 'file-systems' parameter, and remove #:mounts
  parameter.
  [file-system-type-predicate]: New procedure.
  [linux-modules]: Use it.
  Adjust #:mounts argument in 'boot-system' call.
  (gnu-system-initrd): Remove.
* gnu/system/vm.scm (%linux-vm-file-systems): New variable.
  (expression->derivation-in-linux-vm): Adjust call to 'qemu-initrd'.
  (virtualized-operating-system): New procedure.
  (system-qemu-image/shared-store-script)[initrd]: Remove.  Use
  'virtualized-operating-system'.  Get the 'initrd' file from OS-DRV.
* guix/build/linux-initrd.scm (mount-qemu-smb-share, mount-qemu-9p):
  Remove.
  (MS_RDONLY, MS_BIND): New global variables.
  (bind-mount): Remove local 'MS_BIND' definition.
  (mount-root-file-system): New procedure, with code formerly in
  'boot-system'.
  (mount-file-system): New procedure.
  (boot-system): Add #:root-fs-type parameter.  Remove 'MS_RDONLY' local
  variable.  Use 'mount-root-file-system' and 'mount-file-system'.
* doc/guix.texi (Using the Configuration System): Add 'file-system'
  declaration.

system: Add 'sudo' to the setuid programs, and handle /etc/sudoers.

* gnu/system.scm (<operating-system>)[groups]: Change default to just
  the 'root' group.
  [sudoers]: New field.
  (etc-directory): Add #:sudoers parameter.  Add 'sudoers' to the
  file union.
  (operating-system-etc-directory): Pass #:sudoers to 'etc-directory'.
  (%setuid-programs): Add 'sudo'.
  (%sudoers-specification): New variable.
* gnu/system/linux.scm (base-pam-services): Add 'sudo'.
* build-aux/hydra/demo-os.scm: Add 'groups' field; add 'guest' to the
  'wheel' group.

system: Add support for setuid binaries.

* gnu/system.scm (<operating-system>)[pam-services, setuid-programs]:
  New fields.
  (etc-directory)[bashrc]: Prepend /run/setuid-programs to $PATH.
  (operating-system-etc-directory): Honor
  'operating-system-pam-services'.
  (%setuid-programs): New variable.
  (operating-system-boot-script): Add (guix build utils) to the set of
  imported modules.  Call 'activate-setuid-programs' in boot script.
* gnu/system/linux.scm (base-pam-services): New procedure.
* guix/build/activation.scm (%setuid-directory): New variable.
  (activate-setuid-programs): New procedure.
* build-aux/hydra/demo-os.scm: Add 'pam-services' field.

linux-initrd: Rewrite using gexps.

* gnu/system/linux-initrd.scm (expression->initrd): Rename 'inputs'
  parameter to 'to-copy'.  Remove 'files-to-copy'.  Rewrite 'builder' as
  a gexp, and use 'gexp->derivation'.
  (qemu-initrd): Adjust accordingly.

system: grub: Rewrite using gexps.

* gnu/system/grub.scm (grub-configuration-file): Rewrite using
  'gexp->derivation'.
* gnu/system.scm (operating-system-derivation): Adjust accordingly.

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".

vm: Rewrite support procedures to use gexps.

* gnu/system/vm.scm (%imported-modules): Remove.
  (expression->derivation-in-linux-vm): Remove 'inputs' parameter.
  Rename 'imported-modules' to 'modules'.  Rewrite using gexps and
  'gexp->derivation'.
  (qemu-image): Add 'qemu' parameter.  Pass NAME to
  'expression->derivation-in-linux-vm'.  Rewrite using gexps.  Remove
  #:inputs argument to 'expression->derivation-in-linux-vm'.
  (operating-system-default-contents): Rewrite using gexps.
* gnu/system.scm (operating-system-profile-derivation): Rename to...
  (operating-system-profile): ... this.  Adjust callers.
  (operating-system-profile-directory): Remove.

gnu: Use gexps in obvious places in (gnu system ...).

* gnu/system.scm (operating-system-boot-script): Use 'gexp->file'
  instead of 'text-file*'.
* gnu/system/vm.scm (expression->derivation-in-linux-vm): Likewise.
  (system-qemu-image/shared-store-script)[builder]: Turn into a gexp.
  Use 'gexp->derivation' instead of 'derivation-expression'.

vm: Clarify 'system-qemu-image/shared-store-script'.

* gnu/system/vm.scm (system-qemu-image/shared-store-script): Move
  'initrd' definition to the top-level.  Have a single definition of
  'initrd', 'image', and 'os-drv'.

linux-initrd: Mount / as a unionfs when asking for a volatile root.

* guix/build/linux-initrd.scm (make-essential-device-nodes): Make
  /dev/fuse.
  (boot-system): Add #:unionfs parameter.  Invoke UNIONFS instead of
  copying files over when VOLATILE-ROOT? is true.
* gnu/system/linux-initrd.scm (expression->initrd): Add #:inputs
  parameter.
  [files-to-copy]: New procedure.
  [builder]: Add 'to-copy' parameter; honor it.
  (qemu-initrd)[linux-modules]: Add 'fuse.ko' when VOLATILE-ROOT?.
  Pass UNIONFS-FUSE/STATIC as #:inputs; change builder to pass #:unionfs
  to 'boot-system'.