backuptool: introduce addon.d script versioning

* Since A/B addon.d scripts are going to need to do things in a
  specific way or things could go horribly wrong for a user, let's
  introduce versioning so that scripts can claim to be compatible.

* A script can denote it is compatible with addon.d version 2 by
  adding: "# ADDOND_VERSION=2" somewhere in its script.

* Only A/B will require version 2 scripts for now, and version 2
  scripts will still run on non-A/B. Additionally if a script does
  not explicitly denote its version, assume its version 1.

* Version 1: The same old scripts we've always used. We cannot assume
             these will all work with A/B backuptools.

* Version 2: Scripts that denote they are compatible with version 2
             must be aware of the fact that A/B devices will run this
             script for a rom, during a seamless update, mounted at
             /postinstall. The best way to ensure compatibility would
             be to use the pre-designated functions found in the
             backuptool[,_ab].functions scripts.

Change-Id: I5573018dabd21bb64c7c964e2081806072a75243

addonsu/51-addonsu.sh

@@ -1,4 +1,7 @@
 #!/sbin/sh
+#
+# ADDOND_VERSION=2
+#
 
 . /tmp/backuptool.functions
 

prebuilt/common/bin/50-lineage.sh

@@ -1,5 +1,7 @@
 #!/sbin/sh
 #
+# ADDOND_VERSION=2
+#
 # /system/addon.d/50-lineage.sh
 # During a LineageOS 15.1 upgrade, this script backs up /system/etc/hosts,
 # /system is formatted and reinstalled, then the file is restored.

prebuilt/common/bin/backuptool.sh

@@ -7,6 +7,8 @@ export C=/tmp/backupdir
 export S=/system
 export V=15.1
 
+export ADDOND_VERSION=1
+
 # Scripts in /system/addon.d expect to find backuptool.functions in /tmp
 cp -f /tmp/install/bin/backuptool.functions /tmp
 
@@ -15,6 +17,18 @@ preserve_addon_d() {
   if [ -d /system/addon.d/ ]; then
     mkdir -p /tmp/addon.d/
     cp -a /system/addon.d/* /tmp/addon.d/
+
+    # Discard any scripts that aren't at least our version level
+    for f in /postinstall/tmp/addon.d/*sh; do
+      SCRIPT_VERSION=$(grep "^# ADDOND_VERSION=" $f | cut -d= -f2)
+      if [ -z "$SCRIPT_VERSION" ]; then
+        SCRIPT_VERSION=1
+      fi
+      if [ $SCRIPT_VERSION -lt $ADDOND_VERSION ]; then
+        rm $f
+      fi
+    done
+
     chmod 755 /tmp/addon.d/*.sh
   fi
 }

prebuilt/common/bin/backuptool_ab.sh

@@ -7,6 +7,8 @@ export S=/system
 export C=/postinstall/tmp/backupdir
 export V=15.1
 
+export ADDOND_VERSION=2
+
 # Scripts in /system/addon.d expect to find backuptool.functions in /tmp
 mkdir -p /postinstall/tmp/
 cp -f /postinstall/system/bin/backuptool_ab.functions /postinstall/tmp/backuptool.functions
@@ -16,6 +18,18 @@ preserve_addon_d() {
   if [ -d /system/addon.d/ ]; then
     mkdir -p /postinstall/tmp/addon.d/
     cp -a /system/addon.d/* /postinstall/tmp/addon.d/
+
+    # Discard any scripts that aren't at least our version level
+    for f in /postinstall/tmp/addon.d/*sh; do
+      SCRIPT_VERSION=$(grep "^# ADDOND_VERSION=" $f | cut -d= -f2)
+      if [ -z "$SCRIPT_VERSION" ]; then
+        SCRIPT_VERSION=1
+      fi
+      if [ $SCRIPT_VERSION -lt $ADDOND_VERSION ]; then
+        rm $f
+      fi
+    done
+
     chmod 755 /postinstall/tmp/addon.d/*.sh
   fi
 }