A whiteout is an empty file with a special name that signifies
a path that should not be present in upper layers.
When container image layer contains whiteouts (described in [2])
virt-bootstrap should handle them appropriately:
.wh.PATH : PATH should be deleted
.wh..wh..opq : all children (including sub-directories and all
descendants) of the folder containing this file
should be removed.
[1] https://github.com/opencontainers/image-spec/blob/master/layer.md#whiteouts
[2] https://github.com/moby/moby/blob/d1f470946/pkg/archive/whiteouts.go
Signed-off-by: Radostin Stoyanov <rstoyanov1@xxxxxxxxx>
---
src/virtBootstrap/utils.py | 12 ++++-
src/virtBootstrap/whiteout.py | 93 +++++++++++++++++++++++++++++++++++
2 files changed, 103 insertions(+), 2 deletions(-)
create mode 100644 src/virtBootstrap/whiteout.py
diff --git a/src/virtBootstrap/utils.py b/src/virtBootstrap/utils.py
index d6031f1..245d8e0 100644
--- a/src/virtBootstrap/utils.py
+++ b/src/virtBootstrap/utils.py
@@ -35,6 +35,7 @@ import logging
import shutil
import passlib.hosts
+from virtBootstrap import whiteout
try:
import guestfs
@@ -279,8 +280,12 @@ def safe_untar(src, dest):
# Note: Here we use --absolute-names flag to get around the error message
# "Cannot open: Permission denied" when symlynks are extracted, with the
# qemu:/// driver. This flag must not be used outside virt-sandbox.
- params = ['--', '/bin/tar', 'xf', src, '-C', '/mnt', '--exclude', 'dev/*',
- '--overwrite', '--absolute-names']
+ params = ['--', '/bin/tar', 'xf', src,
+ '-C', '/mnt',
+ '--exclude', 'dev/*',
+ '--exclude', '*/%s*' % whiteout.PREFIX,
+ '--overwrite',
+ '--absolute-names']
# Preserve file attributes following the specification in
# https://github.com/opencontainers/image-spec/blob/master/layer.md
if os.geteuid() == 0:
@@ -341,6 +346,9 @@ def untar_layers(layers_list, dest_dir, progress):
tar_file, tar_size = layer
log_layer_extract(tar_file, tar_size, index + 1, nlayers, progress)
+ # Apply whiteout changes with respect to parent layers
+ whiteout.apply_whiteout_changes(tar_file, dest_dir)
+
# Extract layer tarball into destination directory
safe_untar(tar_file, dest_dir)
diff --git a/src/virtBootstrap/whiteout.py b/src/virtBootstrap/whiteout.py
new file mode 100644
index 0000000..1f9efd4
--- /dev/null
+++ b/src/virtBootstrap/whiteout.py
@@ -0,0 +1,93 @@
+# -*- coding: utf-8 -*-
+# Authors: Radostin Stoyanov <rstoyanov1@xxxxxxxxx>
+#
+# Copyright (c) 2019 Radostin Stoyanov
+#
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+
+# 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 General Public License for more details.
+
+# You should have received a copy of the GNU General Public License
+# along with this program. If not, see <http://www.gnu.org/licenses/>.
+
+"""
+Whiteouts are files with a special meaning for a layered filesystem.
+The should not be extracted in the destination directory.
+
+
+import logging
+import os
+import shutil
+import tarfile
+
+
+PREFIX = ".wh."
+METAPREFIX = PREFIX + PREFIX
+OPAQUE = METAPREFIX + ".opq"
+
+# pylint: disable=invalid-name
+logger = logging.getLogger(__name__)
+
+
+def apply_whiteout_changes(tar_file, dest_dir):
+ """
+ Process files with whiteout prefix and apply
+ changes in destination folder.
+ """
+ for path in get_whiteout_files(tar_file):
+ basename = os.path.basename(path)
+ dirname = os.path.dirname(path)
+ dirname = os.path.join(dest_dir, dirname)
+
+ process_whiteout(dirname, basename)
+
+
+def get_whiteout_files(filepath):
+ """
+ Return a list of whiteout files from tar file
+ """
+ whiteout_files = []
+ with tarfile.open(filepath) as tar:
+ for path in tar.getnames():
+ if os.path.basename(path).startswith(PREFIX):
+ whiteout_files.append(path)
+ return whiteout_files
+
+
+def process_whiteout(dirname, basename):
+ """
+ Process a whiteout file:
+
+ .wh.PATH : PATH should be deleted
+ .wh..wh..opq : all children (including sub-directories and all
+ descendants) of the folder containing this file
+ should be removed
+
+ When a folder is first created in a layer an opq file will be
+ generated. In such case, there is nothing to remove we can simply
+ ignore the opque whiteout file.
+ """
+ if basename == OPAQUE:
+ if os.path.isdir(dirname):
+ shutil.rmtree(dirname)
+ os.makedirs(dirname)
+ elif not basename.startswith(METAPREFIX):
+ target = os.path.join(dirname, basename[len(PREFIX):])
+ if os.path.isfile(target):
+ os.remove(target)
+ elif os.path.isdir(target):
+ shutil.rmtree(target)
+ else:
+ logger.error("%s is not a file or directory", target)
