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. + +Whiteout prefix (.wh.) followed by a filename means that the file has +been removed from. + +Whiteout meta prefix (.wh..wh.) has special meaning which is not for +removing a file. +""" + +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) -- 2.21.0 _______________________________________________ virt-tools-list mailing list virt-tools-list@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/virt-tools-list
