Partly fixes <https://bugs.gnu.org/30312>.

* doc/guix.texi (Preparing for Installation): Add note on how to choose
between UEFI and BIOS.
(Using the Configuration System)[Bootloader]: New subsubsection.
(Bootloader Configuration): Expound on the bootloader type and target.
* gnu/system/examples/desktop.tmpl: Switch to UEFI.
* gnu/system/examples/bare-bones.tmpl: Explicitly mention "legacy" and
"BIOS" in the comments.

Reported by Tobias Geerinckx-Rice <me@tobias.gr>
and Björn Höfling <bjoern.hoefling@bjoernhoefling.de>.

* gnu/system/shadow.scm (default-skeletons)["bashrc"]: Use
'--color=auto' instead of '--color'.

* gnu/system/install.scm (os-with-u-boot): New procedure.
* gnu/packages/bootloaders.scm (make-u-boot-package): Export.
* doc/guix.texi (Building the Installation Image for ARM Boards): New
subsection.

Fixes <https://bugs.gnu.org/31714>.
Reported by Vagrant Cascadian <vagrant@debian.org>
and Florian Pelz <pelzflorian@pelzflorian.de>.

* gnu/system/mapped-devices.scm (check-device-initrd-modules): Pass
LINUX-MODULES through 'normalize-module-name'.
* gnu/build/linux-modules.scm (normalize-module-name): Export.

* gnu/build/install.scm (register-closure): Add #:reset-timestamps? and
and #:schema; honor them.  Rewrite in terms of 'register-path'.
(populate-single-profile-directory): Add #:schema and honor it.  Make
/var/guix/profiles and /var/guix/gcroots.
* gnu/build/vm.scm (root-partition-initializer): Pass
 #:reset-timestamps? to 'register-closure'.
* gnu/system/vm.scm (not-config?): New procedure.
(guile-sqlite3&co): New variable.
(expression->derivation-in-linux-vm)[config]: New variable.
[builder]: Use 'with-extensions'.
(iso9660-image)[schema, config]: New variables.
Wrap build expression in 'with-extensions'; add 'sql-schema' call.
Remove GUIX from INPUTS.
(qemu-image)[schema, config]: New variables.
Wrap body in 'with-extensions'.
(system-docker-image)[not-config?]: Remove.
[config]: Use 'make-config.scm'.
[schema]: New variable.
[build]: Use 'with-extensions'.  Add call to 'sql-schema'.  Remove GUIX
from INPUTS.
* gnu/system/file-systems.scm (%store-prefix): Check whether
'%store-prefix' is defined.
* guix/scripts/pack.scm (self-contained-tarball)[not-config?]
[libgcrypt, schema]: New variables.
[build]: Wrap in 'with-extensions'.  Adjust imported module list to use
'make-config.scm' for (guix config).

* gnu/system/vm.scm (expression->derivation-in-linux-vm)
[user-builder]: Define in non-monadic style as 'program-file'.
[loader]: Likewise, and 'execl' USER-BUILDER instead of loading it.
(system-docker-image): Pass BUILD as the second
argument to 'expression->derivation-in-linux-vm'.
(make-iso9660-image, qemu-image): Remove call to 'reboot'.

The previous implementation of 'read-reference-graph' was good enough
for many use cases, but it discarded the graph structure, which is
useful information in some cases.

* guix/build/store-copy.scm (<store-info>): New record type.
(read-reference-graph): Rewrite to return a list of <store-info>.
(closure-size, populate-store): Adjust accordingly.
* gnu/services/base.scm (references-file): Adjust accordingly.
* gnu/system/vm.scm (system-docker-image): Likewise.
* guix/scripts/pack.scm (squashfs-image, docker-image): Likewise.
* tests/gexp.scm ("gexp->derivation #:references-graphs"): Likewise.

This is a followup to commit 1382bde93c3ccb5be6b846b932edd7707fac1a3e,
which disabled automatic sourcing of /etc/bashrc by interactive shell.
The noticeable effect of the change would be that Bash completion would
only work in login shells.

* gnu/system/shadow.scm (default-skeletons)["bashrc"]: Source
/etc/bashrc.

Fixes <https://bugs.gnu.org/31752>.
Regression introduced in commit 8c9bf2946a1cb58c5b7b941db3a37830ece80708.

* gnu/system/vm.scm (iso9660-image): Pass #:file-systems to
'expression->derivation-in-linux-vm'.

* gnu/system/vm.scm (expression->derivation-in-linux-vm): Add
 #:file-systems and use it instead of %LINUX-VM-FILE-SYSTEMS.