Bug#759308: Add option for substring match to prefer Linux kernel versions

[Doug Brunner]

Package: grub-common

Version: 2.02~beta2-11

Severity: wishlist

I (and apparently a number of others, see e.g. http://askubuntu.com/questions/216398/set-older-kernel-as-default-grub-entry) found myself needing to change the Linux kernel version GRUB sets as default. The process is rather clunky and 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.

Testing: Kernels that do not have the substring from GRUB_LINUX_PREF_VERSION_SUBSTR should be ordered below kernels that do. The group of kernels with the substring should be sorted by version, as should kernels without. Specify GRUB_LINUX_PREF_VERSION_SUBSTR=foo in /etc/default/grub and run update-grub.

Patch against git c5b76152c1f9d0cdb999e27a82ea520ab5c4faa4 to implement change follows:
---
diff --git a/util/grub-mkconfig.in b/util/grub-mkconfig.in
index ccce9e5..d31f65c 100644
--- a/util/grub-mkconfig.in
+++ b/util/grub-mkconfig.in
@@ -242,7 +242,8 @@ export GRUB_DEFAULT \
   GRUB_OS_PROBER_SKIP_LIST \
   GRUB_DISABLE_SUBMENU \
   GRUB_RECORDFAIL_TIMEOUT \
-  GRUB_RECOVERY_TITLE
+  GRUB_RECOVERY_TITLE \
+  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 79fa03a..74b26b6 100644
--- a/util/grub.d/10_linux.in
+++ b/util/grub.d/10_linux.in
@@ -269,13 +269,28 @@ EOF
 # 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
   case $linux in
     *.efi.signed)
       # We handle these in linux_entry.
-      list=`echo $list | tr ' ' '\n' | grep -vx $linux | tr '\n' ' '`
       continue
       ;;
   esac

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