Configuration files handling
============================

Configuration files are read from the following locations, ordered by priority:
1. /etc/default/u-boot
2. /usr/share/u-boot-menu/conf.d/*.conf
3. /etc/u-boot-menu/conf.d/*.conf

Each configuration file can contain one or more environment variable and is
sourced by u-boot-update. See u-boot-update(8) for more information about
allowed variables.

Variables values can be overridden by highest-priority configuration files. For
example, if /etc/default/u-boot contains `U_BOOT_DEFAULT=l0` and there is a
file named /usr/share/u-boot-menu/conf.d/new-default.conf containing
`U_BOOT_DEFAULT=l0r`, then the menu entry labelled `l0r` will be set as the
default entry. Moreover, if there is a file named, for example,
/etc/u-boot-menu/conf.d/restore-default.conf containing `U_BOOT_DEFAULT=l1`,
then the default menu entry will be the one labelled `l1`.

This allows flexible configuration management by allowing other packages (for
example, a support package for a specific device) to place configuration
fragment files under /usr/share/u-boot-menu/conf.d/ to override the default
values provided by u-boot-menu, while leaving an option for the end user to
get the final word by creating a configuration fragment file under
/etc/u-boot-menu/conf.d/.

IMPORTANT: In order to avoid situations where the system might be rendered
unbootable by a package removed but not purged, other packages (or downstream
distributions) MUST NOT edit or modify files under /etc as those are meant for
use by end-users only. Instead, it is mandated for such packages to install
their config fragments ONLY under /usr/share/u-boot-menu/conf.d/.