1 files changed, 59 insertions, 0 deletions
diff --git a/nova/filesystem.py b/nova/filesystem.py
new file mode 100644
index 0000000000..5394d2d835
--- /dev/null
+++ b/nova/filesystem.py
@@ -0,0 +1,59 @@
+#    Licensed under the Apache License, Version 2.0 (the "License"); you may
+#    not use this file except in compliance with the License. You may obtain
+#    a copy of the License at
+#
+#         http://www.apache.org/licenses/LICENSE-2.0
+#
+#    Unless required by applicable law or agreed to in writing, software
+#    distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+#    WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+#    License for the specific language governing permissions and limitations
+#    under the License.
+
+"""Functions to address filesystem calls, particularly sysfs."""
+
+import os
+
+from oslo_log import log as logging
+
+from nova import exception
+
+LOG = logging.getLogger(__name__)
+
+
+SYS = '/sys'
+
+
+# NOTE(bauzas): this method is deliberately not wrapped in a privsep entrypoint
+def read_sys(path: str) -> str:
+    """Reads the content of a file in the sys filesystem.
+
+    :param path: relative or absolute. If relative, will be prefixed by /sys.
+    :returns: contents of that file.
+    :raises: nova.exception.FileNotFound if we can't read that file.
+    """
+    try:
+        # The path can be absolute with a /sys prefix but that's fine.
+        with open(os.path.join(SYS, path), mode='r') as data:
+            return data.read()
+    except (OSError, ValueError) as exc:
+        raise exception.FileNotFound(file_path=path) from exc
+
+
+# NOTE(bauzas): this method is deliberately not wrapped in a privsep entrypoint
+# In order to correctly use it, you need to decorate the caller with a specific
+# privsep entrypoint.
+def write_sys(path: str, data: str) -> None:
+    """Writes the content of a file in the sys filesystem with data.
+
+    :param path: relative or absolute. If relative, will be prefixed by /sys.
+    :param data: the data to write.
+    :returns: contents of that file.
+    :raises: nova.exception.FileNotFound if we can't write that file.
+    """
+    try:
+        # The path can be absolute with a /sys prefix but that's fine.
+        with open(os.path.join(SYS, path), mode='w') as fd:
+            fd.write(data)
+    except (OSError, ValueError) as exc:
+        raise exception.FileNotFound(file_path=path) from exc