fix(*): use /media/state and overlays dir

/mnt/stateful_partition was already a little unruly with
/mnt/stateful_partition/home and /mnt/stateful_partition/var_overlay
serving similar functional purposes.

Then we needed to also add /opt and /srv overlays.

I also have wanted to get rid of the ugly and weird
/mnt/stateful_partition name so lets just have one big move.

/mnt/stateful_partition -> /media/state
/mnt/stateful_partition/var_overlay -> /media/overlays/var
/mnt/stateful_partition/home -> /media/overlays/home

From there we add /media/overlays/srv and /media/overlays/opt

boot_nspawn

@@ -28,4 +28,4 @@ STATE="${ROOT}-STATE"
 
 [ -d "$STATE" ] || sudo mkdir -p "$STATE"
 sudo systemd-nspawn --boot --read-only --machine="$HOSTNAME-$BOARD" \
-    --directory="$ROOT" --bind="$STATE:/mnt/stateful_partition"
+    --directory="$ROOT" --bind="$STATE:/media/state"

build_library/base_image_util.sh

@@ -4,6 +4,9 @@
 
 . "${SRC_ROOT}/platform/dev/toolchain_utils.sh" || exit 1
 
+# Overlays are parts of the disk that live on the stateful partition
+ROOT_OVERLAYS=(var opt srv home)
+
 cleanup_mounts() {
   local prev_ret=$?
 
@@ -142,21 +145,28 @@ create_base_image() {
   sudo mount -o loop "${oem_fs_img}" "${oem_fs_dir}"
 
   # Prepare stateful partition with some pre-created directories.
-  sudo mkdir "${stateful_fs_dir}/dev_image"
-  sudo mkdir "${stateful_fs_dir}/var_overlay"
+  for i in ${ROOT_OVERLAYS}; do
+    sudo mkdir -p "${stateful_fs_dir}/overlays/$i"
+    sudo mkdir -p "${root_fs_dir}/$i"
+    sudo mount --bind "${stateful_fs_dir}/overlays/$i" "${root_fs_dir}/$i"
+  done
+
+  sudo mkdir -p "${stateful_fs_dir}/images/dev"
 
   # Create symlinks so that /usr/local/usr based directories are symlinked to
   # /usr/local/ directories e.g. /usr/local/usr/bin -> /usr/local/bin, etc.
-  setup_symlinks_on_root "${stateful_fs_dir}/dev_image" \
-    "${stateful_fs_dir}/var_overlay" "${stateful_fs_dir}"
+  setup_symlinks_on_root "${stateful_fs_dir}/images/dev" \
+    "${stateful_fs_dir}/overlays/var" \
+    "${stateful_fs_dir}"
 
   # Perform binding rather than symlinking because directories must exist
   # on rootfs so that we can bind at run-time since rootfs is read-only.
   info "Binding directories from stateful partition onto the rootfs"
+
+  # Setup the dev image for developer tools
   sudo mkdir -p "${root_fs_dir}/usr/local"
-  sudo mount --bind "${stateful_fs_dir}/dev_image" "${root_fs_dir}/usr/local"
-  sudo mkdir -p "${root_fs_dir}/var"
-  sudo mount --bind "${stateful_fs_dir}/var_overlay" "${root_fs_dir}/var"
+  sudo mount --bind "${stateful_fs_dir}/images/dev" "${root_fs_dir}/usr/local"
+
   sudo mkdir -p "${root_fs_dir}/dev"
 
   info "Binding directories from OEM partition onto the rootfs"

common.sh

@@ -735,7 +735,7 @@ setup_symlinks_on_root() {
   # Give args better names.
   local dev_image_target=$1
   local var_target=$2
-  local dev_image_root="$3/dev_image"
+  local dev_image_root="$3/images/dev"
 
   # If our var target is actually the standard var, we are cleaning up the
   # symlinks (could also check for /usr/local for the dev_image_target).

mount_gpt_image.sh

@@ -179,15 +179,15 @@ mount_image() {
   fi
 
   # Mount directories and setup symlinks.
-  sudo mount --bind "${FLAGS_stateful_mountpt}/var_overlay" \
+  sudo mount --bind "${FLAGS_stateful_mountpt}/overlays/var" \
     "${FLAGS_rootfs_mountpt}/var"
-  sudo mount --bind "${FLAGS_stateful_mountpt}/dev_image" \
+  sudo mount --bind "${FLAGS_stateful_mountpt}/images/dev" \
     "${FLAGS_rootfs_mountpt}/usr/local"
   # Setup symlinks in /usr/local so you can emerge packages into /usr/local.
 
   if [ ${FLAGS_read_only} -eq ${FLAGS_FALSE} ]; then
-    setup_symlinks_on_root "${FLAGS_stateful_mountpt}/dev_image" \
-      "${FLAGS_stateful_mountpt}/var_overlay" "${FLAGS_stateful_mountpt}"
+    setup_symlinks_on_root "${FLAGS_stateful_mountpt}/images/dev" \
+      "${FLAGS_stateful_mountpt}/overlays/var" "${FLAGS_stateful_mountpt}"
   fi
   info "Image specified by ${FLAGS_from} mounted at"\
     "${FLAGS_rootfs_mountpt} successfully."