Prevent local storage setup on non-mounted paths

Fixes #269

storage/local.py

@@ -3,6 +3,7 @@ import shutil
 import hashlib
 import io
 import logging
+import psutil
 
 from uuid import uuid4
 
@@ -145,5 +146,20 @@ class LocalStorage(BaseStorageV2):
     else:
       logger.debug('Content already exists at path: %s', final_path_abs)
 
+  def validate(self):
+    # Load the set of disk mounts.
+    try:
+      mounts = psutil.disk_partitions(all=True)
+    except:
+      logger.exception('Could not load disk partitions')
+      return
 
+    # Verify that the storage's root path is under a mounted Docker volume.
+    for mount in mounts:
+      if mount.mountpoint != '/' and self._root_path.startswith(mount.mountpoint):
+        if mount.device == 'tmpfs':
+          return
 
+    raise Exception('Storage path %s is not under a mounted volume.\n\n'
+                    'Registry data must be stored under a mounted volume '
+                    'to prevent data loss' % self._root_path)