diff --git a/cros.sh b/cros.sh
new file mode 100755
index 0000000..a54f383
--- /dev/null
+++ b/cros.sh
@@ -0,0 +1,61 @@
+#!/bin/bash
+set -e
+
+USE_BITMAP_INDEX=${USE_BITMAP_INDEX:-"0"}
+MANIFEST_URL=$TUNASYNC_UPSTREAM_URL/chromiumos/manifest.git
+MANIFEST_DIR=$TUNASYNC_WORKING_DIR/.manifest
+MANIFEST_XML_REPOLIST=$(dirname $0)/helpers/manifest-xml-repolist.py
+IGNORED_REPO=(
+)
+
+export GIT_TERMINAL_PROMPT=0
+
+function contains() {
+    for e in "${@:2}"; do [[ "$e" == "$1" ]] && return 0; done
+    return 1
+}
+
+function git_clone_or_pull {
+    URL=$1
+    DIRECTORY=$2
+    MIRROR=$3
+    if [[ -z $MIRROR ]]; then
+        if [[ -d $DIRECTORY ]]; then
+            git -C $DIRECTORY pull
+        else
+            git clone $URL $DIRECTORY 
+        fi
+    else
+        if [[ -d $DIRECTORY ]]; then
+            git -C $DIRECTORY remote update
+        else
+            git clone --mirror $URL $DIRECTORY 
+        fi
+    fi
+}
+
+function git_repack() {
+	echo "Start writing bitmap index"
+	while read repo; do 
+		cd $repo
+		size=$(du -sm .|cut -f1)
+		if [[ "$size" -gt "100" ]]; then
+			echo $repo, ${size}M
+			git repack -a -b -d
+		fi
+	done < <(find $TUNASYNC_WORKING_DIR -not -path "$MANIFEST_DIR/.git/*" -type f -name HEAD -exec dirname '{}' ';')
+}
+
+git_clone_or_pull $MANIFEST_URL $MANIFEST_DIR
+
+for repo in $($MANIFEST_XML_REPOLIST $MANIFEST_DIR/default.xml cros chromium); do
+    if [[ -z ${DRY_RUN:-} ]]; then
+        contains $repo ${IGNORED_REPO[@]} && continue
+        git_clone_or_pull $TUNASYNC_UPSTREAM_URL/$repo $TUNASYNC_WORKING_DIR/$repo yes
+        if [[ "$USE_BITMAP_INDEX" == "1" ]]; then
+            git_repack
+        fi
+    else
+        echo $TUNASYNC_UPSTREAM_URL/$repo
+    fi
+done