# -*- Mode:Python; indent-tabs-mode:nil; tab-width:4 -*-
#
# Copyright 2021 Canonical Ltd.
#
# This program is free software; you can redistribute it and/or
# modify it under the terms of the GNU Lesser General Public
# License version 3 as published by the Free Software Foundation.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
# Lesser General Public License for more details.
#
# You should have received a copy of the GNU Lesser General Public License
# along with this program. If not, see <http://www.gnu.org/licenses/>.
"""Overlay handling helpers.
Relevant OCI documentation available at:
https://github.com/opencontainers/image-spec/blob/main/layer.md
"""
import logging
import os
from pathlib import Path
from typing import Set, Tuple
logger = logging.getLogger(__name__)
[docs]def visible_in_layer(lower_dir: Path, upper_dir: Path) -> Tuple[Set[str], Set[str]]:
"""Determine the files and directories that are visible in a layer.
Given a pair of directories containing lower and upper layer entries, list the
files and subdirectories in the lower layer that would be directly visible when
the layers are stacked (i.e. the visibility is not "blocked" by an entry with
the same name that exists in the upper directory). The upper directory may contain
OCI whiteout files and opaque dirs.
:param lower_dir: The lower directory.
:param upper_dir: The upper directory.
:returns: A tuple containing the sets of files and directories that are visible.
"""
visible_files: Set[str] = set()
visible_dirs: Set[str] = set()
logger.debug("check layer visibility in %s", lower_dir)
for root, directories, files in os.walk(lower_dir, topdown=True):
for file_name in files:
path = Path(root, file_name)
relpath = path.relative_to(lower_dir)
if not _is_path_visible(upper_dir, relpath):
continue
upper_path = upper_dir / relpath
if not upper_path.exists() and not oci_whiteout(upper_path).exists():
visible_files.add(str(relpath))
for directory in directories:
path = Path(root, directory)
relpath = path.relative_to(lower_dir)
if not _is_path_visible(upper_dir, relpath):
continue
upper_path = upper_dir / relpath
if not upper_path.exists():
if path.is_symlink():
visible_files.add(str(relpath))
else:
visible_dirs.add(str(relpath))
elif is_oci_opaque_dir(upper_path):
logger.debug("is opaque dir: %s", relpath)
# Don't descend into this directory, overridden by opaque
directories.remove(directory)
logger.debug("layer visibility files=%r, dirs=%r", visible_files, visible_dirs)
return visible_files, visible_dirs
def _is_path_visible(root: Path, relpath: Path) -> bool:
"""Verify if any element of the given path is not whited out.
:param root: The root directory, not included in the verification.
:param relpath: The relative path to verify.
:returns: Whether the final element of the path is visible.
"""
logger.debug("check if path is visible: root=%s, relpath=%s", root, relpath)
levels = len(relpath.parts)
for level in range(levels):
path = Path(root, os.path.join(*relpath.parts[: level + 1]))
if oci_whiteout(path).exists() or is_oci_opaque_dir(path):
logger.debug("is whiteout or opaque: %s", path)
return False
return True
[docs]def is_oci_opaque_dir(path: Path) -> bool:
"""Verify if the given path corresponds to an opaque directory.
:param path: The path of the file to verify.
:returns: Whether the given path is an overlayfs opaque directory.
"""
if not path.is_dir() or path.is_symlink():
return False
return oci_opaque_dir(path).exists()
[docs]def is_oci_whiteout_file(path: Path) -> bool:
"""Verify if the given path corresponds to an OCI whiteout file.
:param path: The path of the file to verify.
:returns: Whether the given path is an OCI whiteout file.
"""
return path.name.startswith(".wh.") and path.name != ".wh..wh..opq"
[docs]def oci_whiteout(path: Path) -> Path:
"""Convert the given path to an OCI whiteout file name.
:param path: The file path to white out.
:returns: The corresponding OCI whiteout file name.
"""
return path.parent / (".wh." + path.name)
[docs]def oci_whited_out_file(whiteout_file: Path) -> Path:
"""Find the whited out file corresponding to a whiteout file.
:param whiteout_file: The whiteout file to process.
:returns: The file that was whited out.
"""
if not whiteout_file.name.startswith(".wh."):
raise ValueError("argument is not an OCI whiteout file")
return whiteout_file.parent / whiteout_file.name[4:]
[docs]def oci_opaque_dir(path: Path) -> Path:
"""Return the OCI opaque directory marker.
:param path: The directory to mark as opaque.
:returns: The corresponding OCI opaque directory marker path.
"""
return path / ".wh..wh..opq"
