diff --git a/prebuilt/common/bin/backuptool.functions b/prebuilt/common/bin/backuptool.functions
index 4319b783..7a915072 100644
--- a/prebuilt/common/bin/backuptool.functions
+++ b/prebuilt/common/bin/backuptool.functions
@@ -34,10 +34,15 @@ restore_file() {
     if [ ! -d "$DIR" ]; then
       mkdir -p "$DIR";
     fi
-    copy_file "$C/$DIR/$FILE" "$1";
+    copy_file "$C/$DIR/$FILE" $(get_output_path "$1");
     if [ -n "$2" ]; then
       echo "Deleting obsolete file $2"
-      rm "$2";
+      rm $(get_output_path "$2");
     fi
   fi
 }
+
+get_output_path() {
+  # In recovery we mounted all partitions in the right place, so we can rely on symlinks
+  echo "$1"
+}
diff --git a/prebuilt/common/bin/backuptool.sh b/prebuilt/common/bin/backuptool.sh
index e0020925..878187f7 100755
--- a/prebuilt/common/bin/backuptool.sh
+++ b/prebuilt/common/bin/backuptool.sh
@@ -8,9 +8,20 @@ export SYSDEV="$(readlink -nf "$2")"
 export SYSFS="$3"
 export V=18.1
 
+export ADDOND_VERSION=3
+
+# Partitions to mount for backup/restore in V3
+export all_V3_partitions="vendor product system_ext"
+
 # Scripts in /system/addon.d expect to find backuptool.functions in /tmp
 cp -f /tmp/install/bin/backuptool.functions /tmp
 
+get_script_version() {
+  version=$(grep "^# ADDOND_VERSION=" $1 | cut -d= -f2)
+  [ -z "$version" ] && version=1
+  echo $version
+}
+
 # Preserve /system/addon.d in /tmp/addon.d
 preserve_addon_d() {
   if [ -d $S/addon.d/ ]; then
@@ -43,15 +54,31 @@ fi
 return 0
 }
 
-# Execute /system/addon.d/*.sh scripts with $1 parameter
-run_stage() {
+# Execute /system/addon.d/*.sh scripts with each $@ parameter
+run_stages() {
 if [ -d /tmp/addon.d/ ]; then
   for script in $(find /tmp/addon.d/ -name '*.sh' |sort -n); do
-    $script $1
+    v=$(get_script_version $script)
+    if [ $v -ge 3 ]; then
+      mount_extra $all_V3_partitions
+    else
+      umount_extra $all_V3_partitions
+    fi
+
+    for stage in $@; do
+      if [ $v -ge 3 ]; then
+        $script $stage
+      else
+        ADDOND_VERSION=2 $script $stage
+      fi
+    done
   done
 fi
 }
 
+#####################
+### Mount helpers ###
+#####################
 determine_system_mount() {
   if grep -q -e"^$SYSDEV" /proc/mounts; then
     umount $(grep -e"^$SYSDEV" /proc/mounts | cut -d" " -f2)
@@ -76,26 +103,77 @@ unmount_system() {
   umount $SYSMOUNT
 }
 
+get_block_for_mount_point() {
+  grep -v "^#" /etc/recovery.fstab | grep " $1 " | tail -n1 | tr -s ' ' | cut -d' ' -f1
+}
+
+find_block() {
+  local name="$1"
+  local fstab_entry=$(get_block_for_mount_point "/$name")
+  # P-SAR hacks
+  [ -z "$fstab_entry" ] && [ "$name" = "system" ] && fstab_entry=$(get_block_for_mount_point "/")
+  [ -z "$fstab_entry" ] && [ "$name" = "system" ] && fstab_entry=$(get_block_for_mount_point "/system_root")
+
+  local dev
+  if [ "$DYNAMIC_PARTITIONS" = "true" ]; then
+    if [ -n "$fstab_entry" ]; then
+      dev="${BLK_PATH}/${fstab_entry}"
+    else
+      dev="${BLK_PATH}/${name}"
+    fi
+  else
+    if [ -n "$fstab_entry" ]; then
+      dev="$fstab_entry"
+    else
+      dev="${BLK_PATH}/${name}"
+    fi
+  fi
+
+  if [ -b "$dev" ]; then
+    echo "$dev"
+  fi
+}
+
 determine_system_mount
 
+DYNAMIC_PARTITIONS=$(getprop ro.boot.dynamic_partitions)
+BLK_PATH=$(dirname "$SYSDEV")
+
+mount_extra() {
+  for partition in $@; do
+    mnt_point="/$partition"
+    mountpoint "$mnt_point" >/dev/null 2>&1 && break
+
+    blk_dev=$(find_block "$partition")
+    if [ -e "$blk_dev" ]; then
+      [ "$DYNAMIC_PARTITIONS" = "true" ] && blockdev --setrw "$blk_dev"
+      mkdir -p "$mnt_point"
+      mount -o rw "$blk_dev" "$mnt_point"
+    fi
+  done
+}
+
+umount_extra() {
+  for partition in $@; do
+    umount -l "/$partition" 2>/dev/null
+  done
+}
+
 case "$1" in
   backup)
     mount_system
     if check_prereq; then
       mkdir -p $C
       preserve_addon_d
-      run_stage pre-backup
-      run_stage backup
-      run_stage post-backup
+      run_stages pre-backup backup post-backup
     fi
     unmount_system
   ;;
   restore)
     mount_system
     if check_prereq; then
-      run_stage pre-restore
-      run_stage restore
-      run_stage post-restore
+      run_stages pre-restore restore post-restore
+      umount_extra $all_V3_partitions
       restore_addon_d
       rm -rf $C
       sync
diff --git a/prebuilt/common/bin/backuptool_ab.functions b/prebuilt/common/bin/backuptool_ab.functions
index a5103f6f..11869c9e 100644
--- a/prebuilt/common/bin/backuptool_ab.functions
+++ b/prebuilt/common/bin/backuptool_ab.functions
@@ -39,10 +39,35 @@ backup_file() {
 
 restore_file() {
   if [ -e "$C/$1" -o -L "$C/$1" ]; then
-    move_file "$C/$1" "/postinstall/$1";
+    move_file "$C/$1" $(get_output_path "$1");
     if [ -n "$2" ]; then
       echo "Deleting obsolete file $2"
-      rm "$2";
+      rm $(get_output_path "$2");
     fi
   fi
 }
+
+get_output_path() {
+  if [ $ADDOND_VERSION -lt 3 ]; then
+    echo "/postinstall/$1"
+    return
+  fi
+
+  file=$(echo "$1" | sed "s|^$S/||")
+  if __is_on_mounted_partition "$file"; then
+    echo "/postinstall/$file"
+  else
+    echo "/postinstall/$1"
+  fi
+}
+
+__is_on_mounted_partition() {
+  for p in $all_V3_partitions; do
+    mnt_point="/postinstall/$p"
+    if echo "$1" | grep -q "^$p/" && [ ! -L "$mnt_point" ] && mountpoint >/dev/null 2>&1 "$mnt_point"; then
+      return 0
+    fi
+  done
+
+  return 1
+}
diff --git a/prebuilt/common/bin/backuptool_ab.sh b/prebuilt/common/bin/backuptool_ab.sh
index 727a8cc2..b4cdba2f 100755
--- a/prebuilt/common/bin/backuptool_ab.sh
+++ b/prebuilt/common/bin/backuptool_ab.sh
@@ -7,26 +7,31 @@ export S=/system
 export C=/postinstall/tmp/backupdir
 export V=18.1
 
-export ADDOND_VERSION=2
+export ADDOND_VERSION=3
+
+# Partitions to mount for backup/restore in V3
+export all_V3_partitions="vendor product system_ext odm oem"
 
 # Scripts in /system/addon.d expect to find backuptool.functions in /tmp
 mkdir -p /postinstall/tmp/
 mountpoint /postinstall/tmp >/dev/null 2>&1 || mount -t tmpfs tmpfs /postinstall/tmp
 cp -f /postinstall/system/bin/backuptool_ab.functions /postinstall/tmp/backuptool.functions
 
+get_script_version() {
+  version=$(grep "^# ADDOND_VERSION=" $1 | cut -d= -f2)
+  [ -z "$version" ] && version=1
+  echo $version
+}
+
 # Preserve /system/addon.d in /tmp/addon.d
 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
+    # Discard any version 1 script, as it is not compatible with a/b
     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
+      if [ $(get_script_version $f) = 1 ]; then
         rm $f
       fi
     done
@@ -58,8 +63,8 @@ fi
 return 0
 }
 
-# Execute /system/addon.d/*.sh scripts with $1 parameter
-run_stage() {
+# Execute /system/addon.d/*.sh scripts with each $@ parameter
+run_stages() {
 if [ -d /postinstall/tmp/addon.d/ ]; then
   for script in $(find /postinstall/tmp/addon.d/ -name '*.sh' |sort -n); do
     # we have no /sbin/sh in android, only recovery
@@ -67,26 +72,110 @@ if [ -d /postinstall/tmp/addon.d/ ]; then
     sed -i '0,/#!\/sbin\/sh/{s|#!/sbin/sh|#!/system/bin/sh|}' $script
     # we can't count on /tmp existing on an A/B device, so utilize /postinstall/tmp as tmpfs
     sed -i 's|. /tmp/backuptool.functions|. /postinstall/tmp/backuptool.functions|g' $script
-    $script $1
+
+    v=$(get_script_version $script)
+    if [ $v -ge 3 ]; then
+      mount_extra $all_V3_partitions
+    else
+      umount_extra $all_V3_partitions
+    fi
+
+    for stage in $@; do
+      if [ $v -ge 3 ]; then
+        $script $stage
+      else
+        ADDOND_VERSION=2 $script $stage
+      fi
+    done
   done
 fi
 }
 
+#####################
+### Mount helpers ###
+#####################
+get_block_for_mount_point() {
+  grep -v "^#" /vendor/etc/fstab.$(getprop ro.boot.hardware) | grep " $1 " | tail -n1 | tr -s ' ' | cut -d' ' -f1
+}
+
+find_block() {
+  local name="$1"
+  local fstab_entry=$(get_block_for_mount_point "/$name")
+  # P-SAR hacks
+  [ -z "$fstab_entry" ] && [ "$name" = "system" ] && fstab_entry=$(get_block_for_mount_point "/")
+  [ -z "$fstab_entry" ] && [ "$name" = "system" ] && fstab_entry=$(get_block_for_mount_point "/system_root")
+
+  local dev
+  if [ "$DYNAMIC_PARTITIONS" = "true" ]; then
+    if [ -n "$fstab_entry" ]; then
+      dev="${BLK_PATH}/${fstab_entry}${SLOT_SUFFIX}"
+    else
+      dev="${BLK_PATH}/${name}${SLOT_SUFFIX}"
+    fi
+  else
+    if [ -n "$fstab_entry" ]; then
+      dev="${fstab_entry}${SLOT_SUFFIX}"
+    else
+      dev="${BLK_PATH}/${name}${SLOT_SUFFIX}"
+    fi
+  fi
+
+  if [ -b "$dev" ]; then
+    echo "$dev"
+  fi
+}
+
+DYNAMIC_PARTITIONS=$(getprop ro.boot.dynamic_partitions)
+if [ "$DYNAMIC_PARTITIONS" = "true" ]; then
+    BLK_PATH="/dev/block/mapper"
+else
+    BLK_PATH=/dev/block/bootdevice/by-name
+fi
+
+CURRENTSLOT=$(getprop ro.boot.slot_suffix)
+if [ ! -z "$CURRENTSLOT" ]; then
+  if [ "$CURRENTSLOT" = "_a" ]; then
+    # Opposite slot
+    SLOT_SUFFIX="_b"
+  else
+    SLOT_SUFFIX="_a"
+  fi
+fi
+
+mount_extra() {
+  for partition in $@; do
+    mnt_point="/postinstall/$partition"
+    mountpoint "$mnt_point" >/dev/null 2>&1 && break
+
+    blk_dev=$(find_block "$partition")
+    if [ -n "$blk_dev" ]; then
+      [ "$DYNAMIC_PARTITIONS" = "true" ] && blockdev --setrw "$blk_dev"
+      mount -o rw "$blk_dev" "$mnt_point"
+    fi
+  done
+}
+
+umount_extra() {
+  for partition in $@; do
+    # Careful with unmounting. If the update has a partition less than the current system,
+    # /postinstall/$partition is a symlink to /system/$partition, which on the active slot
+    # is a symlink to /$partition which is a mountpoint we would end up unmounting!
+    [ ! -L "/postinstall/$partition" ] && umount -l "/postinstall/$partition" 2>/dev/null
+  done
+}
+
 case "$1" in
   backup)
     if check_prereq; then
       mkdir -p $C
       preserve_addon_d
-      run_stage pre-backup
-      run_stage backup
-      run_stage post-backup
+      run_stages pre-backup backup post-backup
     fi
   ;;
   restore)
     if check_prereq; then
-      run_stage pre-restore
-      run_stage restore
-      run_stage post-restore
+      run_stages pre-restore restore post-restore
+      umount_extra $all_V3_partitions
       restore_addon_d
       rm -rf $C
       umount /postinstall/tmp