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util/grub.d/00_header.in: Wire grub.cfg to use env_block when present

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This patch extends the generated grub.cfg so that it can use the
external environment block when the variable env_block is defined.
During boot, if env_block is set, grub.cfg builds a device path for it,
exports the variable, and then loads its contents in addition to the
normal grubenv file.

When GRUB writes variables such as next_entry or saved_entry, the save
commands are changed to write into env_block if it is set, and to fall
back to the grubenv file otherwise. In this way the external environment
block is used automatically, and existing commands like savedefault or
save_env do not need to change.

Signed-off-by: Michael Chang <mchang@suse.com>
Reviewed-by: Neal Gompa <ngompa13@gmail.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>
This commit is contained in:
Michael Chang 2025-10-17 17:01:41 +08:00 committed by Daniel Kiper
parent e4e1776613
commit b634477481
1 changed files with 23 additions and 3 deletions
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20
util/grub.d/00_header.in
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@ -46,6 +46,13 @@ cat << EOF
if [ -s \$prefix/grubenv ]; then
load_env
fi
if [ "\${env_block}" ] ; then
set env_block="(\${root})\${env_block}"
export env_block
load_env -f "\${env_block}"
fi
EOF
if [ "x$GRUB_BUTTON_CMOS_ADDRESS" != "x" ]; then
cat <<EOF
@ -54,7 +61,11 @@ if cmostest $GRUB_BUTTON_CMOS_ADDRESS ; then
elif [ "\${next_entry}" ] ; then
set default="\${next_entry}"
set next_entry=
if [ "\${env_block}" ] ; then
save_env -f "\${env_block}" next_entry
else
save_env next_entry
fi
set boot_once=true
else
set default="${GRUB_DEFAULT}"
@ -65,7 +76,11 @@ else
if [ "\${next_entry}" ] ; then
set default="\${next_entry}"
set next_entry=
if [ "\${env_block}" ] ; then
save_env -f "\${env_block}" next_entry
else
save_env next_entry
fi
set boot_once=true
else
set default="${GRUB_DEFAULT}"
@ -93,8 +108,13 @@ fi
function savedefault {
if [ -z "\${boot_once}" ]; then
saved_entry="\${chosen}"
if [ "\${env_block}" ] ; then
save_env -f "\${env_block}" saved_entry
else
save_env saved_entry
fi
fi
}
function load_video {