templates/kfreebsd: Fix quadratic algorithm for sorting menu items

The current implementation of the 10_kfreebsd script implements its menu
items sorting in bash with a quadratic algorithm, calling "sed", "sort",
"head", and "grep" to compare versions between individual lines, which
is annoyingly slow for kernel developers who can easily end up with
50-100 kernels in their boot partition.

This fix is ported from the 10_linux script, which has a similar
quadratic code pattern.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: debian-bsd@lists.debian.org
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>

util/grub.d/10_kfreebsd.in

@@ -157,10 +157,16 @@ title_correction_code=
 # yet, so it's empty. In a submenu it will be equal to '\t' (one tab).
 submenu_indentation=""
 
+# Perform a reverse version sort on the entire list.
+# Temporarily replace the '.old' suffix by ' 1' and append ' 2' for all
+# other files to order the '.old' files after their non-old counterpart
+# in reverse-sorted order.
+
+reverse_sorted_list=$(echo ${list} | tr ' ' '\n' | sed -e 's/\.old$/ 1/; / 1$/! s/$/ 2/' | version_sort -r | sed -e 's/ 1$/.old/; s/ 2$//')
+
 is_top_level=true
 
-while [ "x$list" != "x" ] ; do
+for kfreebsd in ${reverse_sorted_list}; do
-  kfreebsd=`version_find_latest $list`
   gettext_printf "Found kernel of FreeBSD: %s\n" "$kfreebsd" >&2
   basename=`basename $kfreebsd`
   dirname=`dirname $kfreebsd`
@@ -238,8 +244,6 @@ while [ "x$list" != "x" ] ; do
   if [ "x${GRUB_DISABLE_RECOVERY}" != "xtrue" ]; then
     kfreebsd_entry "${OS}" "${version}" recovery "-s"
   fi
-
-  list=`echo $list | tr ' ' '\n' | fgrep -vx "$kfreebsd" | tr '\n' ' '`
 done
 
 # If at least one kernel was found, then we need to