Merge "Adds temporary chown to sparse_copy."

nova/utils.py

@@ -1523,3 +1523,23 @@ def read_file_as_root(file_path):
         return out
     except exception.ProcessExecutionError:
         raise exception.FileNotFound(file_path=file_path)
+
+
+@contextlib.contextmanager
+def temporary_chown(path, owner_uid=None):
+    """Temporarily chown a path.
+
+    :params owner_uid: UID of temporary owner (defaults to current user)
+    """
+    if owner_uid is None:
+        owner_uid = os.getuid()
+
+    orig_uid = os.stat(path).st_uid
+
+    if orig_uid != owner_uid:
+        execute('chown', owner_uid, path, run_as_root=True)
+    try:
+        yield
+    finally:
+        if orig_uid != owner_uid:
+            execute('chown', orig_uid, path, run_as_root=True)

nova/virt/xenapi/vm_utils.py

@@ -1651,6 +1651,11 @@ def _sparse_copy(src_path, dst_path, virtual_size, block_size=4096):
                 "virtual_size=%(virtual_size)d block_size=%(block_size)d"),
                 locals())
 
+    # NOTE(sirp): we need read/write access to the devices; since we don't have
+    # the luxury of shelling out to a sudo'd command, we temporarily take
+    # ownership of the devices.
+    with utils.temporary_chown(src_path):
+        with utils.temporary_chown(dst_path):
             with open(src_path, "r") as src:
                 with open(dst_path, "w") as dst:
                     data = src.read(min(block_size, left))