templates: Introduce GRUB_TOP_LEVEL_* vars

A user may wish to use an image that is not sorted as the "latest"
version as the top-level entry. For example, in Arch Linux, if a user
has the LTS and regular kernels installed, "/boot/vmlinuz-linux-lts"
gets sorted as the "latest" compared to "/boot/vmlinuz-linux", meaning
the LTS kernel becomes the top-level entry. However, a user may wish to
use the regular kernel as the top-level default with the LTS only
existing as a backup.

This need can be seen in Arch Linux's AUR with two user-submitted
packages[0][1] providing an update hook which patches /etc/grub.d/10_linux
to move the desired kernel to the top-level. This patch serves to solve
this in a more generic way.

Introduce the GRUB_TOP_LEVEL, GRUB_TOP_LEVEL_XEN and GRUB_TOP_LEVEL_OS_PROBER
variables to allow users to specify the top-level entry.

Create grub_move_to_front() as a helper function which moves entries to
the front of a list. This function does the heavy lifting of moving
the menu entry to the front in each script.

In 10_netbsd, since there isn't an explicit list variable, extract the
items that are being iterated through into a list so that we can
optionally apply grub_move_to_front() to the list before the loop.

[0]: https://aur.archlinux.org/packages/grub-linux-default-hook
[1]: https://aur.archlinux.org/packages/grub-linux-rt-default-hook

Signed-off-by: Denton Liu <liu.denton@gmail.com>
Reviewed-by: Oskari Pirhonen <xxc3ncoredxx@gmail.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>

docs/grub.texi

@@ -1444,6 +1444,16 @@ for all respectively normal entries.
 The values of these options replace the values of @samp{GRUB_CMDLINE_LINUX}
 and @samp{GRUB_CMDLINE_LINUX_DEFAULT} for Linux and Xen menu entries.
 
+@item GRUB_TOP_LEVEL
+@item GRUB_TOP_LEVEL_XEN
+This option should be an absolute path to a kernel image. If provided, the
+image specified will be made the top-level entry if it is found in the scan.
+
+@item GRUB_TOP_LEVEL_OS_PROBER
+This option should be a line of output from @command{os-prober}. As
+@samp{GRUB_TOP_LEVEL}, if provided, the image specified will be made the
+top-level entry if it is found in the scan.
+
 @item GRUB_EARLY_INITRD_LINUX_CUSTOM
 @itemx GRUB_EARLY_INITRD_LINUX_STOCK
 List of space-separated early initrd images to be loaded from @samp{/boot}.

util/grub-mkconfig.in

@@ -233,6 +233,9 @@ export GRUB_DEFAULT \
   GRUB_CMDLINE_NETBSD \
   GRUB_CMDLINE_NETBSD_DEFAULT \
   GRUB_CMDLINE_GNUMACH \
+  GRUB_TOP_LEVEL \
+  GRUB_TOP_LEVEL_XEN \
+  GRUB_TOP_LEVEL_OS_PROBER \
   GRUB_EARLY_INITRD_LINUX_CUSTOM \
   GRUB_EARLY_INITRD_LINUX_STOCK \
   GRUB_TERMINAL_INPUT \

util/grub-mkconfig_lib.in

@@ -218,6 +218,32 @@ version_sort ()
    esac
 }
 
+# Given an item as the first argument and a list as the subsequent arguments,
+# returns the list with the first argument moved to the front if it exists in
+# the list.
+grub_move_to_front ()
+{
+  item="$1"
+  shift
+
+  item_found=false
+  for i in "$@"; do
+    if [ "x$i" = "x$item" ]; then
+      item_found=true
+    fi
+  done
+
+  if [ "x$item_found" = xtrue ]; then
+    echo "$item"
+  fi
+  for i in "$@"; do
+    if [ "x$i" = "x$item" ]; then
+      continue
+    fi
+    echo "$i"
+  done
+}
+
 # One layer of quotation is eaten by "" and the second by sed; so this turns
 # ' into \'.
 grub_quote () {

util/grub.d/10_hurd.in

@@ -229,6 +229,10 @@ submenu_indentation=""
 
 reverse_sorted_kernels=$(echo ${kernels} | tr ' ' '\n' | sed -e 's/\.old$/ 1/; / 1$/! s/$/ 2/' | version_sort -r | sed -e 's/ 1$/.old/; s/ 2$//')
 
+if [ "x$GRUB_TOP_LEVEL" != x ]; then
+  reverse_sorted_kernels=$(grub_move_to_front "$GRUB_TOP_LEVEL" ${reverse_sorted_kernels})
+fi
+
 is_top_level=true
 
 for kernel in ${reverse_sorted_kernels}; do

util/grub.d/10_kfreebsd.in

@@ -164,6 +164,10 @@ submenu_indentation=""
 
 reverse_sorted_list=$(echo ${list} | tr ' ' '\n' | sed -e 's/\.old$/ 1/; / 1$/! s/$/ 2/' | version_sort -r | sed -e 's/ 1$/.old/; s/ 2$//')
 
+if [ "x$GRUB_TOP_LEVEL" != x ]; then
+  reverse_sorted_list=$(grub_move_to_front "$GRUB_TOP_LEVEL" ${reverse_sorted_list})
+fi
+
 is_top_level=true
 
 for kfreebsd in ${reverse_sorted_list}; do

util/grub.d/10_linux.in

@@ -202,6 +202,10 @@ submenu_indentation=""
 
 reverse_sorted_list=$(echo $list | tr ' ' '\n' | sed -e 's/\.old$/ 1/; / 1$/! s/$/ 2/' | version_sort -r | sed -e 's/ 1$/.old/; s/ 2$//')
 
+if [ "x$GRUB_TOP_LEVEL" != x ]; then
+  reverse_sorted_list=$(grub_move_to_front "$GRUB_TOP_LEVEL" ${reverse_sorted_list})
+fi
+
 is_top_level=true
 for linux in ${reverse_sorted_list}; do
   gettext_printf "Found linux image: %s\n" "$linux" >&2

util/grub.d/10_netbsd.in

@@ -146,8 +146,14 @@ pattern="^ELF[^,]*executable.*statically linked"
 # yet, so it's empty. In a submenu it will be equal to '\t' (one tab).
 submenu_indentation=""
 
+list="/netbsd $(ls -t /netbsd?* 2>/dev/null)"
+
+if [ "x$GRUB_TOP_LEVEL" != x ]; then
+  list=$(grub_move_to_front "$GRUB_TOP_LEVEL" ${list})
+fi
+
 is_top_level=true
-for k in /netbsd $(ls -t /netbsd?* 2>/dev/null) ; do
+for k in ${list}; do
   if ! grub_file_is_not_garbage "$k" ; then
     continue
   fi

util/grub.d/20_linux_xen.in

@@ -245,6 +245,13 @@ submenu_indentation=""
 reverse_sorted_xen_list=$(echo ${xen_list} | tr ' ' '\n' | sed -e 's/\.old$/ 1/; / 1$/! s/$/ 2/' | version_sort -r | sed -e 's/ 1$/.old/; s/ 2$//')
 reverse_sorted_linux_list=$(echo ${linux_list} | tr ' ' '\n' | sed -e 's/\.old$/ 1/; / 1$/! s/$/ 2/' | version_sort -r | sed -e 's/ 1$/.old/; s/ 2$//')
 
+if [ "x$GRUB_TOP_LEVEL_XEN" != x ]; then
+  reverse_sorted_xen_list=$(grub_move_to_front "$GRUB_TOP_LEVEL_XEN" ${reverse_sorted_xen_list})
+fi
+if [ "x$GRUB_TOP_LEVEL" != x ]; then
+  reverse_sorted_linux_list=$(grub_move_to_front "$GRUB_TOP_LEVEL" ${reverse_sorted_linux_list})
+fi
+
 is_top_level=true
 
 for current_xen in ${reverse_sorted_xen_list}; do

util/grub.d/30_os-prober.in

@@ -113,6 +113,10 @@ EOF
 
 used_osprober_linux_ids=
 
+if [ "x$GRUB_TOP_LEVEL_OS_PROBER" != x ]; then
+  OSPROBED=$(grub_move_to_front "$GRUB_TOP_LEVEL_OS_PROBER" ${OSPROBED})
+fi
+
 for OS in ${OSPROBED} ; do
   DEVICE="`echo ${OS} | cut -d ':' -f 1`"
   LONGNAME="`echo ${OS} | cut -d ':' -f 2 | tr '^' ' '`"