grubby-bls: expand kernel options if these are environment variables

The grub2 bootloader allows the BLS snippets fields to contain environment
variables instead of constants. This is useful for example to define the
kernel command line parameters only once in the grubenv file and set this
variable in the BLS snippets.

But this can be confusing for users when the information is printed by the
grubby script, so expand the variables if they can be looked up in grubenv.

Resolves: rhbz#1649785

Signed-off-by: Javier Martinez Canillas <javierm@redhat.com>

grubby-bls

@@ -216,6 +216,20 @@ get_prefix() {
     fi
 }
 
+expand_var() {
+    local var=$1
+
+    if [[ $bootloader == "grub2" ]]; then
+        local value="$(grub2-editenv "${env}" list | grep ${var##$} | sed -e "s/${var##$}=//")"
+        value="$(echo ${value} | sed -e 's/\//\\\//g')"
+        if [[ -n $value ]]; then
+            var="$value"
+        fi
+    fi
+
+    echo $var
+}
+
 display_info_values() {
     local indexes=($(param_to_indexes "$1"))
     local prefix=$(get_prefix)
@@ -226,9 +240,19 @@ display_info_values() {
 
     for i in ${indexes[*]}; do
         local root=""
+        local value=""
         local args=${bls_options[$i]}
         local opts=(${args})
 
+        for opt in ${opts[*]}; do
+            if [[ $opt =~ ^\$ ]]; then
+                value="$(expand_var $opt)"
+                args="$(echo ${args} | sed -e "s/${opt}/${value}/")"
+            fi
+        done
+
+        local opts=(${args})
+
         for opt in ${opts[*]}; do
             if echo $opt | grep -q "^root="; then
                 root="$(echo $opt | sed -e 's/root=//')"
@@ -443,7 +467,7 @@ update_args() {
 
 get_bls_args() {
     if [[ $bootloader = "grub2" && "${bls_options[$i]}" = "\$kernelopts" ]]; then
-        old_args=$(grub2-editenv list | grep kernelopts)
+        old_args=$(grub2-editenv "${env}" list | grep kernelopts)
         old_args="${old_args##kernelopts=}"
     else
         old_args="${bls_options[$i]}"