[PATCH] Add config option to prefer Linux kernel versions by substring match

[Doug Brunner <doug@doug-brunner.com>]

Hi all,

First time submitting - please let me know if I'm doing anything wrong.

This patch adds an option, GRUB_LINUX_PREF_VERSION_SUBSTR, that can be set to prioritize Linux kernels containing a
given substring. This takes precedence over version ordering, so if you have 3.14.1-generic, 3.14.2-generic,
3.8.13-fnord1, and 3.8.13-fnord2 and the substring is 'fnord', the order is:
3.8.13-fnord2
3.8.13-fnord1
3.14.2-generic
3.14.1-generic

Rationale: I and others, (see e.g. http://askubuntu.com/questions/216398/set-older-kernel-as-default-grub-entry) needed
to change the Linux kernel version GRUB sets as default. The process is error-prone: you have to figure out where in the
GRUB menu it will appear, then enter that in /etc/default/grub, and if the menu position changes due to new kernels
added to the system you have to do it all over again. I had older kernels with a distinctive local version naming scheme
that I wanted preferred over the stock kernels, but it could also be used to specify a particular kernel version.

* util/grub-mkconfig.in: Add export of GRUB_LINUX_PREF_VERSION_SUBSTR
* util/grub.d/10_linux.in: Handle GRUB_LINUX_PREF_VERSION_SUBSTR when adding kernels

Signed-off-by: Doug Brunner <doug@doug-brunner.com>
---
 util/grub-mkconfig.in   |  3 ++-
 util/grub.d/10_linux.in | 22 ++++++++++++++++++----
 2 files changed, 20 insertions(+), 5 deletions(-)

diff --git a/util/grub-mkconfig.in b/util/grub-mkconfig.in
index d1fae49..9a3a3e9 100644
--- a/util/grub-mkconfig.in
+++ b/util/grub-mkconfig.in
@@ -224,7 +224,8 @@ export GRUB_DEFAULT \
   GRUB_ENABLE_CRYPTODISK \
   GRUB_BADRAM \
   GRUB_OS_PROBER_SKIP_LIST \
-  GRUB_DISABLE_SUBMENU
+  GRUB_DISABLE_SUBMENU \
+  GRUB_LINUX_PREF_VERSION_SUBSTR
 
 if test "x${grub_cfg}" != "x"; then
   rm -f "${grub_cfg}.new"
diff --git a/util/grub.d/10_linux.in b/util/grub.d/10_linux.in
index d2e2a8f..0c447f6 100644
--- a/util/grub.d/10_linux.in
+++ b/util/grub.d/10_linux.in
@@ -173,9 +173,25 @@ title_correction_code=
 # yet, so it's empty. In a submenu it will be equal to '\t' (one tab).
 submenu_indentation=""
 
+pref_list=""
+non_pref_list=""
+for entry in $list; do
+  if [[ "$entry" == *$GRUB_LINUX_PREF_VERSION_SUBSTR* ]]; then
+    pref_list="$pref_list $entry"
+  else
+    non_pref_list="$non_pref_list $entry"
+  fi
+done
+
 is_top_level=true
-while [ "x$list" != "x" ] ; do
-  linux=`version_find_latest $list`
+while [ "x$pref_list$non_pref_list" != "x" ] ; do
+  if [ "x$pref_list" != "x" ]; then
+    linux=`version_find_latest $pref_list`
+    pref_list=`echo $pref_list | tr ' ' '\n' | fgrep -vx "$linux" | tr '\n' ' '`
+  else
+    linux=`version_find_latest $non_pref_list`
+    non_pref_list=`echo $non_pref_list | tr ' ' '\n' | fgrep -vx "$linux" | tr '\n' ' '`
+  fi
   gettext_printf "Found linux image: %s\n" "$linux" >&2
   basename=`basename $linux`
   dirname=`dirname $linux`
@@ -240,8 +256,6 @@ while [ "x$list" != "x" ] ; do
     linux_entry "${OS}" "${version}" recovery \
                 "single ${GRUB_CMDLINE_LINUX}"
   fi
-
-  list=`echo $list | tr ' ' '\n' | fgrep -vx "$linux" | tr '\n' ' '`
 done
 
 # If at least one kernel was found, then we need to