system: Add btrfs file system support.

* gnu/build/file-systems.scm (%btrfs-endianness, btrfs-superblock?,
  read-btrfs-superblock, btrfs-superblock-uuid,
  btrfs-superblock-volume-name, check-btrfs-file-system): New variables.
  (%paritition-label-readers, %partition-uuid-readers): Add btrfs
  readers.
* gnu/system/linux-initrd.scm (linux-modules): Add btrfs modules when a
  btrfs file-system is used.
* gnu/tests/install.scm (%btrfs-root-os %btrfs-root-os-source,
  %btrfs-root-installation-script, %test-btrfs-root-os): New system
  test.
* doc/guix.texi: Adjust accordingly.

Fixes <http://bugs.gnu.org/19280>.

system: grub: Load relevant EFI modules on EFI systems.

* gnu/system/grub.scm (eye-candy)[setup-gfxterm-body]: Add 'insmod'
invocations when ${grub_platform} is "efi".

install: The list of services is now a plain list.

* gnu/system/install.scm (installation-services): Rename to...
(%installation-services): ... this.  Turn into a list instead of a thunk.

linux-initrd: Support FAT filesystems.

* gnu/system/linux-initrd.scm (base-initrd): When a FAT filesystem is
present: Add fatfsck/static in 'helper-packages'; and add nls_iso8859-1
in 'linux-modules'.

install: Add dosfstools.

* gnu/system/install.scm (installation-os)[packages]: Add DOSFSTOOLS.

Merge branch 'master' into staging

Merge branch 'master' into python-build-system

doc: Suggest installing gvfs.

* gnu/system/examples/desktop.tmpl: Add gvfs to the system-wide list of
packages.

Merge branch 'master' into python-build-system

doc: Document encrypted root partitions.

This is a followup to f7f292d359e0eb77617f4ecf6b3164f868ec1784.

* doc/guix.texi (Preparing for Installation): Give commands for
encrypted root installation.
(Proceeding with the Installation): Add item about mapped devices.
(File Systems): Mention that 'dependencies' can list <mapped-device>
objects.
* gnu/system/examples/desktop.tmpl (mapped-devices): New field.
(file-systems): Add 'dependencies' field.

Merge branch 'master' into staging

mapped-devices: Use 'cryptsetup-static' in 'luks-device-mapping'.

* gnu/system/mapped-devices.scm (open-luks-device): Use
CRYPTSETUP-STATIC instead of CRYPTSETUP.  Use 'file-append'.
(close-luks-device): Likewise.

vm: Disable initrd-time QEMU networking for VM images.

Fixes <http://bugs.gnu.org/24943>.
Reported by dian_cecht@zoho.com.

* gnu/system/vm.scm (system-qemu-image)[initrd]: Remove
 #:qemu-networking? #t.
(virtualized-operating-system): Likewise

container: Pass a list of <file-system> objects as things to mount.

* gnu/build/linux-container.scm (mount-file-systems): 'mounts' is now a
list of <file-system> objects instead of a list of lists ("specs").
Add call to 'file-system->spec' as the argument to 'mount-file-system'.
(run-container, call-with-container): Adjust docstring accordingly.
* gnu/system/file-systems.scm (spec->file-system): New procedure.
* gnu/system/linux-container.scm (container-script)[script]: Call
'spec->file-system' inside gexp.
* guix/scripts/environment.scm (launch-environment/container): Remove
call to 'file-system->spec'.
* tests/containers.scm ("call-with-container, mnt namespace")
("call-with-container, mnt namespace, wrong bind mount"): Pass a list of
<file-system> objects.

linux-container: Use 'source-module-closure' when generating the script.

* gnu/system/linux-container.scm (container-script)[script]: Use
'source-module-closure' in 'with-imported-modules' form.

system: Use grub from bootloader configuration.

* gnu/system/grub.scm (gnu): Export grub-configuration-grub.
* guix/scripts/system.scm (perform-action): Use it.
(define-module): Don't import (gnu packages grub).

Co-authored-by: Danny Milosavljevic <dannym@scratchpost.org>

Merge branch 'master' into core-updates

gnu: Remove comment which is factually incorrect.

* gnu/system/pam.scm: Remove incorrect comment.

Merge branch 'master' into core-updates

system: Record store file system info in each generation.

* gnu/system.scm (<boot-parameters>)[store-device, store-mount-point]:
New fields.
(read-boot-parameters): Initialize them.
(operating-system-grub.cfg): Likewise.  Remove STORE-FS argument from
call to 'grub-configuration-file'.
(operating-system-parameters-file): Add 'store' element in
'boot-parameters'.
* gnu/system/grub.scm (strip-mount-point): Replace 'store-fs' parameter
by 'mount-point'; adjust accordingly.  Adjust callers.
(<menu-entry>)[device, device-mount-point]: New fields.
(eye-candy): Replace 'root-fs' parameter by 'store-device'; add
'store-mount-point'.  Use keyword arguments for 'system' and 'port'.
(grub-root-search): Remove 'root-fs' by 'device' and adjust
accordingly.
(grub-configuration-file): Remove 'store-fs' parameter.  Adjust
accordingly.
* guix/scripts/system.scm (previous-grub-entries): Initialize 'device'
and 'device-mount-point' fields from PARAMS.
* doc/guix.texi (GRUB Configuration): Document 'device' and
'device-mount-point'.  Explain that 'linux' can be prefixed by a GRUB
device name.

Co-authored-by: Ludovic Courtès <ludo@gnu.org>