BCF-6655: Default GRUB boot entry is changed after BMR

usr/share/rear/conf/default.conf

@@ -3476,25 +3476,35 @@ readonly BACKUP_RESTORE_MOVE_AWAY_DIRECTORY="$VAR_DIR/moved_away_after_backup_re
 # (because such stuff is considered as outdated leftover e.g. from a previous recovery)
 # but already existing stuff in the BACKUP_RESTORE_MOVE_AWAY_DIRECTORY that is not
 # in the current BACKUP_RESTORE_MOVE_AWAY_FILES list is kept.
-# Example:
-# Probably stuff in the /var/tmp directory is not needed after a system recovery
-# and /etc/udev/rules.d/70-persistent-net.rules is created and maintained
+#
+# Examples:
+#
+# Probably stuff in the /var/tmp directory is not needed after a system recovery:
+# BACKUP_RESTORE_MOVE_AWAY_FILES+=( /var/tmp )
+#
+# /etc/udev/rules.d/70-persistent-net.rules is created and maintained
 # by systemd/udev (see https://github.com/rear/rear/issues/770):
-# BACKUP_RESTORE_MOVE_AWAY_FILES=( /var/tmp /etc/udev/rules.d/70-persistent-net.rules )
+# BACKUP_RESTORE_MOVE_AWAY_FILES+=( /etc/udev/rules.d/70-persistent-net.rules )
 #
-# Move away outdated information from previous boot via GRUB2
-# to avoid a possible GRUB2 "error: invalid environment block."
-# cf. https://github.com/rear/rear/issues/1828
+# Move away outdated information from a previous boot via GRUB2:
+# BACKUP_RESTORE_MOVE_AWAY_FILES+=( /boot/grub/grubenv /boot/grub2/grubenv )
+# This avoids a possible GRUB2 message "error: invalid environment block."
+# which should be harmless because the system should boot nevertheless
+# (cf. https://github.com/rear/rear/issues/1828#issuecomment-398717889).
 # GRUB2 can use /boot/grub/grubenv or /boot/grub2/grubenv
 # to remember a small amount of information from one boot to the next.
-# But on a by "rear recover" recreated system there is no such thing
-# as a meaningful previous boot (because "rear recover" recreates a system
-# by reinstalling it completely from scratch) so that there is no meaningful
-# use-case to remember any information from a possible previous boot,
-# cf. https://github.com/rear/rear/issues/1828#issuecomment-399050741
-# Nevertheless that information from the last boot on the original system
-# could be still of interest for the user so that it is not deleted:
-BACKUP_RESTORE_MOVE_AWAY_FILES=( /boot/grub/grubenv /boot/grub2/grubenv )
+# Because "rear recover" recreates the system by reinstalling it from scratch
+# it could cause booting issues when possibly outdated information from a
+# previous boot of the original system is still used in the recreated system
+# (cf. https://github.com/rear/rear/issues/1828#issuecomment-399050741).
+# On the other hand GRUB2 relies on grubenv for certain special stuff.
+# For example grubenv may contain essential information,
+# such as saved_entry, default or kernelopts.
+# So grubenv can be considered as part of the GRUB2 configuration.
+# Therefore grubenv should not be moved away by default
+# (for details see https://github.com/rear/rear/issues/3578).
+#
+BACKUP_RESTORE_MOVE_AWAY_FILES=()
 ####
 
 ####

usr/share/rear/finalize/Linux-i386/665_set_grubenv.sh

@@ -0,0 +1,55 @@
+# Set up grubenv (GRUB environment block)
+
+function set_grubenv() {
+    local grubenv_file="$VAR_DIR/recovery/grubenv"
+
+    # A non-existing grubenv_file is considered OK because it exists only
+    # if env_block was set.
+    if [ ! -f "$grubenv_file" ]; then
+        return 0
+    fi
+
+    local grub_editenv
+    if ! grub_editenv=$(get_grub_editenv); then
+        LogPrintError "Failed to set grubenv: neither grub-editenv nor grub2-editenv was found"
+        return 1
+    fi
+
+    # Remove grubenv from the restored filesystem before setting variables
+    local restored_grubenv
+    for restored_grubenv in /boot/grub2/grubenv /boot/grub/grubenv; do
+        restored_grubenv="${TARGET_FS_ROOT}${restored_grubenv}"
+        if [ -f "$restored_grubenv" ]; then
+            rm "$restored_grubenv"
+            Log "'$restored_grubenv' was removed"
+        fi
+    done
+
+    # It is essential to set up the environment block in the reserved btrfs sector
+    # See https://en.opensuse.org/GRUB#GRUB2_on_btrfs_/boot for more details
+    chroot "$TARGET_FS_ROOT" /bin/bash -c "\"$grub_editenv\" - unset dummy"
+
+    local exit_code=0
+    local var_value
+    while IFS= read -r var_value; do
+        local var="${var_value%=*}"
+        # env_block is read-only after initialization
+        if [ "$var" = "env_block" ] ; then
+            continue
+        fi
+        if ! chroot "$TARGET_FS_ROOT" /bin/bash -c "\"$grub_editenv\" - set \"$var_value\""; then
+            LogPrintError "Failed to set '$var_value' to grubenv"
+            exit_code=1
+        fi
+    done < "$grubenv_file"
+
+    if [ $exit_code -eq 0 ]; then
+        Log "grubenv was set successfully"
+    fi
+
+    return $exit_code
+}
+
+if is_grub2_used; then
+    set_grubenv
+fi

usr/share/rear/layout/save/default/700_save_grubenv.sh

@@ -0,0 +1,40 @@
+# Save grubenv (GRUB environment block) to $VAR_DIR/recovery/grubenv.
+# See https://www.gnu.org/software/grub/manual/grub/html_node/Environment-block.html
+# for more details about grubenv.
+
+function list_grubenv() {
+    local grub_editenv
+    if ! grub_editenv=$(get_grub_editenv); then
+        LogPrintError "Failed to list grubenv: neither grub-editenv nor grub2-editenv was found"
+        return 1
+    fi
+
+    "$grub_editenv" - list
+}
+
+# env_block sets the external raw block where GRUB can store environment block.
+# See https://www.gnu.org/software/grub/manual/grub/html_node/env_005fblock.html
+# for more details about env_block.
+function is_fs_envblock_used() {
+    list_grubenv | grep -q "^env_block="
+}
+
+function save_grubenv() {
+    local grubenv_file="$VAR_DIR/recovery/grubenv"
+
+    if ! list_grubenv > "$grubenv_file"; then
+        LogPrintError "Failed to save grubenv to '$grubenv_file'"
+        return 1
+    fi
+
+    Log "grubenv was successfully saved to '$grubenv_file'"
+    return 0
+}
+
+# Save grubenv only if Btrfs envblock is used, because the envblock
+# located in the Btrfs header is not accessible during recovery. In other cases,
+# the envblock is located at /boot/grub/envblock or /boot/grub2/envblock,
+# which is backed up and restored as a regular file.
+if is_grub2_used && is_fs_envblock_used; then
+    save_grubenv
+fi

usr/share/rear/lib/bootloader-functions.sh

@@ -1018,4 +1018,48 @@ function get_sysconfig_bootloader() {
     echo "$sysconfig_bootloader"
 }
 
+: "${GRUB_EDITENV_PATH:=""}"
+
+function get_grub_editenv() {
+    # Check cached path first
+    if [ -n "$GRUB_EDITENV_PATH" ]; then
+        echo "$GRUB_EDITENV_PATH"
+        return 0
+    fi
+
+    local grub_editenv_path="type -P grub-editenv || type -P grub2-editenv"
+
+    if test "$RECOVERY_MODE"; then
+        GRUB_EDITENV_PATH="$(chroot "$TARGET_FS_ROOT" /bin/bash -c "$grub_editenv_path")"
+    else
+        GRUB_EDITENV_PATH="$($grub_editenv_path)"
+    fi
+
+    if [ -z "$GRUB_EDITENV_PATH" ]; then
+        return 1
+    fi
+
+    echo "$GRUB_EDITENV_PATH"
+}
+
+function is_grub2_used() {
+    local bootloader_path="$VAR_DIR/recovery/bootloader"
+
+    if [ ! -f "$bootloader_path" ]; then
+        return 1
+    fi
+
+    local used_bootloader
+    used_bootloader="$( cat "$bootloader_path" )"
+
+    case $used_bootloader in
+        (GRUB2|GRUB2-EFI)
+            return 0
+            ;;
+        (*)
+            return 1
+            ;;
+    esac
+}
+
 # vim: set et ts=4 sw=4