monads: Add 'text-file*'.

* guix/monads.scm (text-file*): New procedure.
* tests/monads.scm ("text-file*"): New test.
* doc/guix.texi (The Store Monad): Change example since the previous one
  would erroneously fail to retain a reference to Coreutils.  Document
  'text-file*'.

gnu: file: Upgrade to 5.16.

* gnu/packages/file.scm (file): Upgrade to 5.16.

Signed-off-by: Ludovic Courtès <ludo@gnu.org>

gnu: gtkmm-2 New variable

* gnu/packages/gtk.scm (gtkmm-2): New variable.

Signed-off-by: Ludovic Courtès <ludo@gnu.org>

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: Add xterm.

* gnu/packages/xorg.scm (xterm): New variable.

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.

offload: Have 'build-machines' honor its argument.

* guix/scripts/offload.scm (build-machines): Honor FILE.

gnu: linux-initrd: Build /dev/input devices.

* guix/build/linux-initrd.scm (make-essential-device-nodes): Make
  dev/input devices.

gnu: Add preliminary Xorg service.

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

gnu: linux-initrd: Make /dev/{mem,kmem}.

* guix/build/linux-initrd.scm (make-essential-device-nodes): Make
  dev/{mem,kmem}.

gnu: xorg-server: Use /var as $localstatedir.

* gnu/packages/xorg.scm (xorg-server): Pass --localstatedir=/var.  In
  'configure' phase, patch 'hw/xfree86/Makefile.in'.

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.

gnu: linux-initrd: Allow the root file system to be volatile.

* gnu/system/linux-initrd.scm (qemu-initrd): Add 'volatile-root?'
  parameter.
* guix/build/linux-initrd.scm (boot-system): Likewise.  Honor it.

gnu: linux: Really build 9p/virtio modules.

* gnu/packages/linux.scm (linux-libre): Add CONFIG_NET_9P and
  CONFIG_9P_FS.

gnu: linux-initrd: Recognize 9p file systems.

* gnu/system/linux-initrd.scm (qemu-initrd)[virtio-9p-modules]: New
  variable.
  [linux-modules]: Append VIRTIO-9P-MODULES when a 9p file system is in
  MOUNTS.
* guix/build/linux-initrd.scm (mount-qemu-9p): New procedure.
  (boot-system): Recognize '9p' in MOUNTS, and use 'mount-qemu-9p'.

gnu: linux-initrd: Match kernel module file names exactly.

* gnu/system/linux-initrd.scm (expression->initrd)[string->regexp]: New
  procedure.  Use it in the call to 'find-files'.

gnu: linux-initrd: Properly distinguish between /dev/sda* and /dev/vda*.

* guix/build/linux-initrd.scm (make-essential-device-nodes): Rename
  devices with major = 8 to /dev/sda*.  Make /dev/vda* devices.
* gnu/system/vm.scm (qemu-image): Change '/dev/vda' to '/dev/sda'.
* gnu/system.scm (operating-system-derivation): Likewise.

gnu: linux-initrd: Start a REPL when the root could not be mounted.

* guix/build/linux-initrd.scm (boot-system): Catch errors when mounting
  ROOT and call 'start-repl' upon error.

gnu: linux-libre: Build more virtio modules.

* gnu/packages/linux.scm (linux-libre): Append CONFIG_NET_9P_VIRTIO and
  CONFIG_VIRTIO_{NET,BLK,BALLOON} to '.config'.

gnu: vm: Run QEMU with '-enable-kvm'.

* gnu/system/vm.scm (expression->derivation-in-linux-vm): Pass QEMU
  '-enable-kvm'.