kernel-install: add a new $ENTRY_TOKEN variable for naming boot entries

This cleans up naming of boot loader spec boot entries a bit (i.e. the
naming of the .conf snippet files, and the directory in $BOOT where the
kernel images and initrds are placed), and isolates it from the actual machine
ID concept.

Previously there was a sinlge concept for both things, because typically
the entries are just named after the machine ID. However one could also
use a different identifier, i.e. not a 128bit ID in which cases issues
pop up everywhere. For example, the "machine-id" field in the generated
snippets would not be a machine ID anymore, and the newly added
systemd.machine_id= kernel parameter would possibly get passed invalid
data.

Hence clean this up:

$MACHINE_ID → always a valid 128bit ID.

$ENTRY_TOKEN → usually the $MACHINE_ID but can be any other string too.
This is used to name the directory to put kernels/initrds in. It's also
used for naming the *.conf snippets that implement the Boot Loader Type
1 spec.

src/kernel-install/90-loaderentry.install

@@ -29,6 +29,7 @@ INITRD_OPTIONS_SHIFT=4
 [ "$KERNEL_INSTALL_LAYOUT" = "bls" ] || exit 0
 
 MACHINE_ID="$KERNEL_INSTALL_MACHINE_ID"
+ENTRY_TOKEN="$KERNEL_INSTALL_ENTRY_TOKEN"
 BOOT_ROOT="$KERNEL_INSTALL_BOOT_ROOT"
 
 BOOT_MNT="$(stat -c %m "$BOOT_ROOT")"
@@ -41,10 +42,10 @@ fi
 case "$COMMAND" in
     remove)
         [ "$KERNEL_INSTALL_VERBOSE" -gt 0 ] && \
-            echo "Removing $BOOT_ROOT/loader/entries/$MACHINE_ID-$KERNEL_VERSION*.conf"
+            echo "Removing $BOOT_ROOT/loader/entries/$ENTRY_TOKEN-$KERNEL_VERSION*.conf"
         exec rm -f \
-            "$BOOT_ROOT/loader/entries/$MACHINE_ID-$KERNEL_VERSION.conf" \
-            "$BOOT_ROOT/loader/entries/$MACHINE_ID-$KERNEL_VERSION+"*".conf"
+            "$BOOT_ROOT/loader/entries/$ENTRY_TOKEN-$KERNEL_VERSION.conf" \
+            "$BOOT_ROOT/loader/entries/$ENTRY_TOKEN-$KERNEL_VERSION+"*".conf"
         ;;
     add)
         ;;
@@ -80,9 +81,9 @@ if [ -r /etc/kernel/tries ]; then
         echo "/etc/kernel/tries does not contain an integer." >&2
         exit 1
     fi
-    LOADER_ENTRY="$BOOT_ROOT/loader/entries/$MACHINE_ID-$KERNEL_VERSION+$TRIES.conf"
+    LOADER_ENTRY="$BOOT_ROOT/loader/entries/$ENTRY_TOKEN-$KERNEL_VERSION+$TRIES.conf"
 else
-    LOADER_ENTRY="$BOOT_ROOT/loader/entries/$MACHINE_ID-$KERNEL_VERSION.conf"
+    LOADER_ENTRY="$BOOT_ROOT/loader/entries/$ENTRY_TOKEN-$KERNEL_VERSION.conf"
 fi
 
 if ! [ -d "$ENTRY_DIR_ABS" ]; then

src/kernel-install/kernel-install

@@ -97,7 +97,19 @@ fi
 [ -z "$MACHINE_ID" ] && [ -r /etc/machine-id ]   && read -r MACHINE_ID </etc/machine-id
 [ -z "$MACHINE_ID" ] && MACHINE_ID="$(systemd-id128 new)"
 
-[ -z "$BOOT_ROOT" ] && for suff in "$MACHINE_ID" "loader/entries"; do
+# Now that we determined the machine ID to use, let's determine the "token" for
+# the boot loader entry to generate. We use that for naming the directory below
+# $BOOT where we want to place the kernel/initrd and related resources, as well
+# for naming the .conf boot loader spec entry. Typically this is just the
+# machine ID, but it can be anything else, too, if we are told so.
+[ -z "$ENTRY_TOKEN" ] && [ -r /etc/kernel/entry-token ] && read -r ENTRY_TOKEN </etc/kernel/entry-token
+[ -z "$ENTRY_TOKEN" ] && ENTRY_TOKEN="$MACHINE_ID"
+
+# NB: The $MACHINE_ID is guaranteed to be a valid machine ID, but
+#     $ENTRY_TOKEN can be any string that fits into a VFAT filename, though
+#     typically is just the machine ID.
+
+[ -z "$BOOT_ROOT" ] && for suff in "$ENTRY_TOKEN" "loader/entries"; do
     for pref in "/efi" "/boot" "/boot/efi" ; do
         if [ -d "$pref/$suff" ]; then
             BOOT_ROOT="$pref"
@@ -117,14 +129,14 @@ done
 
 if [ -z "$layout" ]; then
     # Administrative decision: if not present, some scripts generate into /boot.
-    if [ -d "$BOOT_ROOT/$MACHINE_ID" ]; then
+    if [ -d "$BOOT_ROOT/$ENTRY_TOKEN" ]; then
         layout="bls"
     else
         layout="other"
     fi
 fi
 
-ENTRY_DIR_ABS="$BOOT_ROOT/$MACHINE_ID/$KERNEL_VERSION"
+ENTRY_DIR_ABS="$BOOT_ROOT/$ENTRY_TOKEN/$KERNEL_VERSION"
 
 # Provide a directory where to store generated initrds
 cleanup() {
@@ -136,6 +148,7 @@ trap cleanup EXIT
 KERNEL_INSTALL_STAGING_AREA="$(mktemp -d -t -p /tmp kernel-install.staging.XXXXXXX)"
 
 export KERNEL_INSTALL_MACHINE_ID="$MACHINE_ID"
+export KERNEL_INSTALL_ENTRY_TOKEN="$ENTRY_TOKEN"
 export KERNEL_INSTALL_BOOT_ROOT="$BOOT_ROOT"
 export KERNEL_INSTALL_LAYOUT="$layout"
 export KERNEL_INSTALL_INITRD_GENERATOR="$initrd_generator"
@@ -168,7 +181,7 @@ case "$COMMAND" in
         fi
 
         if [ "$MAKE_ENTRY_DIR_ABS" -eq 0 ]; then
-            # Compatibility with earlier versions that used the presence of $BOOT_ROOT/$MACHINE_ID
+            # Compatibility with earlier versions that used the presence of $BOOT_ROOT/$ENTRY_TOKEN
             # to signal to 00-entry-directory to create $ENTRY_DIR_ABS
             # to serve as the indication to use or to not use the BLS
             if [ "$KERNEL_INSTALL_VERBOSE" -gt 0 ]; then