[PATCH] Add support for specifying the boot device by label

[darkpenguin]

Specifying the boot device by its label rather than its UUID can be
pretty useful in various situations (e.g. multiple test VMs).

This might have to be adapted a little to meet the coding standards I'm
not familiar with. Please feel free to improve it in any way you want.

This patch works for me on an older version of grub2 (=2.06-13 in Debian
Bookworm), but it's rather trivial, and only touches two parts that are
otherwise untouched for ages.

- Specify "GRUB_DISABLE_LINUX_UUID=LABEL" in /etc/default/grub
- It will attempt to use a label instead of UUID
- If a device with the necessary label is not found in
/dev/disk/by-label/ , it falls back to using UUID
- If you just assigned new labels, run 'partprobe' to populate
/dev/disk/by-label/ properly

The decision to reuse GRUB_DISABLE_LINUX_UUID was because:
1) This is more of an addition on top of UUID rather than "disabling"
it, it still uses UUID internally, and it falls back to UUID
2) I could not come up with a better way to do it
3) I could not figure out how to source other variables from
/etc/defaults/grub and why not all of them are there. :)


---
diff --git a/util/grub-mkconfig_lib.in b/util/grub-mkconfig_lib.in
index 0895328..bd43bc0 100644
--- a/util/grub-mkconfig_lib.in
+++ b/util/grub-mkconfig_lib.in
@@ -158,14 +158,22 @@ prepare_grub_to_access_device ()
   fi
   if [ "x${GRUB_DISABLE_UUID}" != "xtrue" ] &&
fs_uuid="`"${grub_probe}" --device $@ --target=fs_uuid 2> /dev/null`" ; then
     hints="`"${grub_probe}" --device $@ --target=hints_string 2>
/dev/null`" || hints=
+
+    if [ "x${GRUB_DISABLE_LINUX_UUID}" = "xLABEL" ] \
+        && [ -b "/dev/disk/by-label/$(blkid -l -t UUID=${fs_uuid} -s
LABEL -o value)" ]; then
+      device="--label $(blkid -l -t UUID=${fs_uuid} -s LABEL -o value)"
+    else
+      device="--fs-uuid ${fs_uuid}"
+    fi
+
     if [ "x$hints" != x ]; then
       echo "if [ x\$feature_platform_search_hint = xy ]; then"
-      echo "  search --no-floppy --fs-uuid --set=root ${hints} ${fs_uuid}"
+      echo "  search --no-floppy --set=root ${hints} ${device}"
       echo "else"
-      echo "  search --no-floppy --fs-uuid --set=root ${fs_uuid}"
+      echo "  search --no-floppy --set=root ${device}"
       echo "fi"
     else
-      echo "search --no-floppy --fs-uuid --set=root ${fs_uuid}"
+      echo "search --no-floppy --set=root ${device}"
     fi
   fi
   IFS="$old_ifs"
diff --git a/util/grub.d/10_linux.in b/util/grub.d/10_linux.in
index cc393be..d29a004 100644
--- a/util/grub.d/10_linux.in
+++ b/util/grub.d/10_linux.in
@@ -61,6 +61,9 @@ if ( [ "x${GRUB_DEVICE_UUID}" = "x" ] && [
"x${GRUB_DEVICE_PARTUUID}" = "x" ] )
 elif [ "x${GRUB_DEVICE_UUID}" = "x" ] \
     || [ "x${GRUB_DISABLE_LINUX_UUID}" = "xtrue" ]; then
   LINUX_ROOT_DEVICE=PARTUUID=${GRUB_DEVICE_PARTUUID}
+elif [ "x${GRUB_DISABLE_LINUX_UUID}" = "xLABEL" ] \
+    && [ -b "/dev/disk/by-label/$(blkid -l -t UUID=${GRUB_DEVICE_UUID}
-s LABEL -o value)" ]; then
+  LINUX_ROOT_DEVICE=LABEL="$(blkid -l -t UUID=${GRUB_DEVICE_UUID} -s
LABEL -o value)"
 else
   LINUX_ROOT_DEVICE=UUID=${GRUB_DEVICE_UUID}
 fi