This patch handles the case where the LUKS encrypted root partition was
unlocked by GRUB, allowing to load the kernel and initrd.
In this case GRUB set root like to /dev/mapper/cryptroot in the command line.

If the intrd tree includes a LUKS keyfile use that, else we should set CRYPTDEV
to $(basename $root) so that ROOTDEV be /dev/mapper$CRYPTDEV in the mount
command
Didier Spaier

--- ./init	2018-04-18 20:55:09.661574000 +0200
+++ ./init.new	2021-02-11 00:37:33.753687578 +0100
@@ -76,7 +76,12 @@
 INITRD=$(cat /initrd-name)
 ROOTDEV=$(cat /rootdev)
 ROOTFS=$(cat /rootfs)
-LUKSDEV=$(cat /luksdev)
+if grep -q : luksdev; then
+  LUKSDEV=$(cat /luksdev|cut -d: -f1)
+  LUKSNAME=$(cat /luksdev|cut -d: -f2)
+else
+  LUKSDEV=$(cat /luksdev)
+fi
 LUKSTRIM=$(cat /lukstrim 2>/dev/null)
 LUKSKEY=$(cat /lukskey)
 RESUMEDEV=$(cat /resumedev)
@@ -193,8 +198,9 @@
   # partitions or mdadm arrays.
   # Unavailable devices such as LVM Logical Volumes will need to be
   # deferred until they become available after the vgscan.
-
-  if [ -x /sbin/cryptsetup ]; then
+  
+  [ "$LUKSKEY" ] && ! echo "$LUKSKEY" |grep -q "^/dev" && KEYININITRD="y"
+  if [ -x /sbin/cryptsetup ] && [ ! "$KEYININITRD" ] ; then
 
     # Determine if we have to use a LUKS keyfile:
     if [ ! -z "$LUKSKEY" ]; then
@@ -229,6 +235,8 @@
           CRYPTDEV="luks$(basename $LUKSDEV)"
         elif [ "x$ROOTDEV" = "x$(basename $ROOTDEV)" ]; then
           CRYPTDEV="$ROOTDEV"
+        elif echo $ROOTDEV | grep -q "^/dev/mapper/"; then
+          CRYPTDEV=$(basename $ROOTDEV)
         else
           CRYPTDEV="luks$(basename $LUKSDEV)"
         fi
@@ -252,6 +260,12 @@
     done
   fi
 
+  if [ -x /sbin/cryptsetup ] && [ "$KEYININITRD" ] ; then
+    [ ! "$LUKSNAME" ] && LUKSNAME=cryptroot
+    echo "Unlocking the root partition."
+    cryptsetup open --key-file "$LUKSKEY" "$LUKSDEV" "$LUKSNAME"
+  fi 
+
   # Initialize LVM:
   if [ -x /sbin/vgchange ]; then
     mkdir -p /var/lock/lvm	# this avoids useless warnings