doc: cookbook: Add entry about Wireguard VPN.

Co-authored-by: Brice Waegeneire <brice@waegenei.re>

* doc/guix-cookbook.texi (Connect to Wireguard VPN): New section.

services: nfs: Expose configuration options for TCP and UDP.

* gnu/services/nfs.scm (<nfs-configuration>)[nfsd-tcp?, nfsd-udp?]: New
fields.
(nfs-shepherd-services)[rpc.nfsd]: Populate the --{no-,}tcp and --{no-,}udp
command line options based on the values of the nfsd-tcp? and nfsd-upd?
fields.
* doc/guix.texi (Network File System): Add doc.

doc: Add example to calculate the size a system.

* doc/guix.texi (Invoking `guix size'): Add guix size example for store item.

doc: Remove explicit support for mips64el-linux.

It's been a good run, but no one is maintaining the architecture.
So long, and thanks for all the fish.

* doc/guix.texi (GNU Distribution): Change text for mips64el-linux
to denote it is deprecated.
(Daemon Offload Setup): Change occurrences of mips64el-linux to
aarch64-linux and adjust local code snippets.
(Guix Environment)[cross-compilation]: Change mips64el-linux-gnu to
aarch64-linux-gnu.
(GNU Build System)(package-cross-derivation]: Same.
(G-Expressions)[cross compilation]: Same.
(Additional Build Options)[cross-compilation, build logs]: Same.
(qemu-binfmt-service-type): Remove mips64el.
* doc/contributing.texi (Submitting Patches): Same.
* m4/guix.m4: (GUIX_ASSERT_SUPPORTED_SYSTEM): Remove mips64el-linux.

doc: Use existing URLs and file names in installation instructions.

Some users are confused that these URLs and file names don't work, so
change them to the most popular architecture, while still mentioning
alternatives.

* doc/guix.texi (USB Stick and DVD Installation, Binary Installation): Use
x86_64-linux URLs by default.

doc: Remove one use of 'file-append*'.

* doc/build.scm (texinfo-manual-source)[build]: Use 'file-append', not
'file-append*', for 'htmlxref.cnf', to ensure it has the right basename.

doc: Fix typos.

* doc/guix.texi: Fix typos.
* doc/contributing.texi: Fix typos.

Signed-off-by: Julien Lepiller <julien@lepiller.eu>

pull: Protect against downgrade attacks.

* guix/scripts/pull.scm (%default-options): Add 'validate-pull'.
(%options, show-help): Add '--allow-downgrades'.
(warn-about-backward-updates): New procedure.
(guix-pull): Pass #:current-channels and #:validate-pull to
'latest-channel-instances'.
* guix/channels.scm (ensure-forward-channel-update): Add hint for
when (channel-commit channel) is true.
* doc/guix.texi (Invoking guix pull): Document '--allow-downgrades'.

doc: cookbook: Add subsection about session locking with xss-lock.

* doc/guix-cookbook.texi (Session lock): New node.

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

doc: Update to the new 'grub-theme' procedure.

This is a follow-up commit to 9cdb10d52e34f7e8fa3b6238fe268646a4bbb877:
gnu: grub: Allow a PNG image and replace "aspect-ratio" with "resolution".

* doc/guix.texi (Bootloader Configuration): Describe and use the 'grub-theme'
procedure instead of the removed '%default-theme' variable.

doc: Update 'Bootstrapping' for further binary seed reduction.

* doc/images/gcc-core-mesboot0-graph.dot: New image, replacing
* doc/images/gcc-mesboot0-bag-graph.dot: ... remove file.
* doc/local.mk (DOT_FILES): Update for new image file.
* doc/guix.texi (Reduced Binary Seed Bootstrap): Use it in updated description
of further reduction of the trusted computing base.

packages: Introduce <content-hash> and use it in <origin>.

* guix/packages.scm (<content-hash>): New record type.
(define-content-hash-constructor, build-content-hash)
(content-hash): New macros.
(print-content-hash): New procedure.
(<origin>): Rename constructor to '%origin'.
[sha256]: Remove field.
[hash]: New field.  Adjust users.
(origin-compatibility-helper, origin): New macros.
(origin-sha256): New deprecated procedure.
(origin->derivation): Adjust accordingly.
* tests/packages.scm ("package-source-derivation, origin, sha512"): New
test.
* guix/tests.scm: Hide (gcrypt hash) 'sha256' for proper syntax
matching.
* tests/challenge.scm: Add #:prefix for (gcrypt hash) and adjust users.
* tests/derivations.scm: Likewise.
* tests/store.scm: Likewise.
* tests/graph.scm ("bag DAG, including origins"): Provide 'sha256' field
with the right length.
* gnu/packages/aspell.scm (aspell-dictionary)
(aspell-dict-ca, aspell-dict-it): Use 'hash' and 'content-hash' for
proper syntax matching.
* gnu/packages/bash.scm (bash-patch): Rename 'sha256' to 'sha256-bv'.
* gnu/packages/bootstrap.scm (bootstrap-executable): Rename 'sha256' to 'bv'.
* gnu/packages/readline.scm (readline-patch): Likewise.
* gnu/packages/virtualization.scm (qemu-patch): Rename 'sha256' to
'sha256-bv'.
* guix/import/utils.scm: Hide (gcrypt hash) 'sha256'.

guix hash, guix download: Support base64 format.

* guix/scripts/download.scm (show-help, %options): Support "base64"
format.
* guix/scripts/hash.scm (show-help, %options): Likewise.
* tests/guix-hash.sh: Test it.
* doc/guix.texi (Invoking guix hash): Document it.

guix hash, guix download: Add '--hash'.

* guix/scripts/download.scm (%default-options): Add 'hash-algorithm'.
(show-help, %options): Add "--hash".
(guix-download): Honor it.
* guix/scripts/hash.scm (%default-options): Add 'hash-algorithm'.
(show-help, %options): Add "--hash".
(guix-hash): Honor it.
* tests/guix-hash.sh: Test '-H sha512'.
* doc/guix.texi (Invoking guix download): Document it.
(Invoking guix hash): Document it.

maint: Add "make check-channel-news".

* build-aux/check-channel-news.scm: New file.
* Makefile.am (EXTRA_DIST): Add it.
(check-channel-news): New phony rule.
* doc/contributing.texi (Commit Access): Mention "make check-channel-news".

doc: Use "Alternatively" instead of "Alternately".

These two words have different meanings and we really meant
"alternatively" here.

* doc/guix.texi (System Installation):
(Preparing for Installation):
(Invoking guix refresh):
(Invoking guix challenge):
(Networking Services): "Alternatively", not "Alternately".

bootloader: grub: Allow booting from a Btrfs subvolume.

* gnu/bootloader/grub.scm (strip-mount-point): Remove procedure.
(normalize-file): Add procedure.
(grub-configuration-file): New BTRFS-SUBVOLUME-FILE-NAME parameter.  When
defined, prepend its value to the kernel and initrd file names, using the
NORMALIZE-FILE procedure.  Adjust the call to EYE-CANDY to pass the
BTRFS-SUBVOLUME-FILE-NAME argument.  Normalize the KEYMAP file as well.
(eye-candy): Add a BTRFS-SUBVOLUME-FILE-NAME parameter, and use it, along with
the NORMALIZE-FILE procedure, to normalize the FONT-FILE and IMAGE nested
variables.  Adjust doc.
* gnu/bootloader/depthcharge.scm (depthcharge-configuration-file): Adapt.
* gnu/bootloader/extlinux.scm (extlinux-configuration-file): Likewise.
* gnu/system/file-systems.scm (btrfs-subvolume?)
(btrfs-store-subvolume-file-name): New procedures.
* gnu/system.scm (operating-system-bootcfg): Specify the Btrfs
subvolume file name the store resides on to the
`operating-system-bootcfg' procedure, using the new
BTRFS-SUBVOLUME-FILE-NAME argument.
* doc/guix.texi (File Systems): Add a Btrfs subsection to document the use of
subvolumes.
* gnu/tests/install.scm (%btrfs-root-on-subvolume-os)
(%btrfs-root-on-subvolume-os-source)
(%btrfs-root-on-subvolume-installation-script)
(%test-btrfs-root-on-subvolume-os): New variables.

file-systems: Add helpers for parsing the options string into an alist.

* gnu/system/file-systems.scm (file-system-options->alist)
(alist->file-system-options): New procedures.
* tests/file-systems.scm: New tests.
* doc/guix.texi (File Systems): Add note about the newly added procedures.

linux-boot: Refactor boot-system.

The --root option can now be omitted, and inferred from the root file system
declaration instead.

* gnu/build/file-systems.scm (canonicalize-device-spec): Extend to support NFS
directly, and...
* gnu/build/linux-boot.scm (boot-system): ...remove NFS special casing from
here.  Remove nested definitions for root-fs-type, root-fs-flags and
root-fs-options, and bind those inside the let* instead.  Make "--root" take
precedence over the device field string representation of the root file
system.
* doc/guix.texi (Initial RAM Disk): Document that "--root" can be left
unspecified.

guix describe: Add '--list-formats'

* guix/scripts/describe.scm (%available-formats): New variable.
(list-formats): New procedure.
(%options, show-help): Add --list-formats
* doc/guix.texi: Add --list-formats

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