Merge pull request #4310 from nalind/manifest-lists

Move to containers/image v5, support manifest lists

18 files changed, 1787 insertions, 0 deletions

diff --git a/vendor/github.com/containerd/continuity/fs/copy.go b/vendor/github.com/containerd/continuity/fs/copy.go
new file mode 100644
index 000000000..ad61022ad
--- /dev/null
+++ b/vendor/github.com/containerd/continuity/fs/copy.go
@@ -0,0 +1,172 @@
+/*
+   Copyright The containerd Authors.
+
+   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.
+*/
+
+package fs
+
+import (
+	"io/ioutil"
+	"os"
+	"path/filepath"
+	"sync"
+
+	"github.com/pkg/errors"
+)
+
+var bufferPool = &sync.Pool{
+	New: func() interface{} {
+		buffer := make([]byte, 32*1024)
+		return &buffer
+	},
+}
+
+// XAttrErrorHandlers transform a non-nil xattr error.
+// Return nil to ignore an error.
+// xattrKey can be empty for listxattr operation.
+type XAttrErrorHandler func(dst, src, xattrKey string, err error) error
+
+type copyDirOpts struct {
+	xeh XAttrErrorHandler
+}
+
+type CopyDirOpt func(*copyDirOpts) error
+
+// WithXAttrErrorHandler allows specifying XAttrErrorHandler
+// If nil XAttrErrorHandler is specified (default), CopyDir stops
+// on a non-nil xattr error.
+func WithXAttrErrorHandler(xeh XAttrErrorHandler) CopyDirOpt {
+	return func(o *copyDirOpts) error {
+		o.xeh = xeh
+		return nil
+	}
+}
+
+// WithAllowXAttrErrors allows ignoring xattr errors.
+func WithAllowXAttrErrors() CopyDirOpt {
+	xeh := func(dst, src, xattrKey string, err error) error {
+		return nil
+	}
+	return WithXAttrErrorHandler(xeh)
+}
+
+// CopyDir copies the directory from src to dst.
+// Most efficient copy of files is attempted.
+func CopyDir(dst, src string, opts ...CopyDirOpt) error {
+	var o copyDirOpts
+	for _, opt := range opts {
+		if err := opt(&o); err != nil {
+			return err
+		}
+	}
+	inodes := map[uint64]string{}
+	return copyDirectory(dst, src, inodes, &o)
+}
+
+func copyDirectory(dst, src string, inodes map[uint64]string, o *copyDirOpts) error {
+	stat, err := os.Stat(src)
+	if err != nil {
+		return errors.Wrapf(err, "failed to stat %s", src)
+	}
+	if !stat.IsDir() {
+		return errors.Errorf("source is not directory")
+	}
+
+	if st, err := os.Stat(dst); err != nil {
+		if err := os.Mkdir(dst, stat.Mode()); err != nil {
+			return errors.Wrapf(err, "failed to mkdir %s", dst)
+		}
+	} else if !st.IsDir() {
+		return errors.Errorf("cannot copy to non-directory: %s", dst)
+	} else {
+		if err := os.Chmod(dst, stat.Mode()); err != nil {
+			return errors.Wrapf(err, "failed to chmod on %s", dst)
+		}
+	}
+
+	fis, err := ioutil.ReadDir(src)
+	if err != nil {
+		return errors.Wrapf(err, "failed to read %s", src)
+	}
+
+	if err := copyFileInfo(stat, dst); err != nil {
+		return errors.Wrapf(err, "failed to copy file info for %s", dst)
+	}
+
+	for _, fi := range fis {
+		source := filepath.Join(src, fi.Name())
+		target := filepath.Join(dst, fi.Name())
+
+		switch {
+		case fi.IsDir():
+			if err := copyDirectory(target, source, inodes, o); err != nil {
+				return err
+			}
+			continue
+		case (fi.Mode() & os.ModeType) == 0:
+			link, err := getLinkSource(target, fi, inodes)
+			if err != nil {
+				return errors.Wrap(err, "failed to get hardlink")
+			}
+			if link != "" {
+				if err := os.Link(link, target); err != nil {
+					return errors.Wrap(err, "failed to create hard link")
+				}
+			} else if err := CopyFile(target, source); err != nil {
+				return errors.Wrap(err, "failed to copy files")
+			}
+		case (fi.Mode() & os.ModeSymlink) == os.ModeSymlink:
+			link, err := os.Readlink(source)
+			if err != nil {
+				return errors.Wrapf(err, "failed to read link: %s", source)
+			}
+			if err := os.Symlink(link, target); err != nil {
+				return errors.Wrapf(err, "failed to create symlink: %s", target)
+			}
+		case (fi.Mode() & os.ModeDevice) == os.ModeDevice:
+			if err := copyDevice(target, fi); err != nil {
+				return errors.Wrapf(err, "failed to create device")
+			}
+		default:
+			// TODO: Support pipes and sockets
+			return errors.Wrapf(err, "unsupported mode %s", fi.Mode())
+		}
+		if err := copyFileInfo(fi, target); err != nil {
+			return errors.Wrap(err, "failed to copy file info")
+		}
+
+		if err := copyXAttrs(target, source, o.xeh); err != nil {
+			return errors.Wrap(err, "failed to copy xattrs")
+		}
+	}
+
+	return nil
+}
+
+// CopyFile copies the source file to the target.
+// The most efficient means of copying is used for the platform.
+func CopyFile(target, source string) error {
+	src, err := os.Open(source)
+	if err != nil {
+		return errors.Wrapf(err, "failed to open source %s", source)
+	}
+	defer src.Close()
+	tgt, err := os.Create(target)
+	if err != nil {
+		return errors.Wrapf(err, "failed to open target %s", target)
+	}
+	defer tgt.Close()
+
+	return copyFileContent(tgt, src)
+}
diff --git a/vendor/github.com/containerd/continuity/fs/copy_linux.go b/vendor/github.com/containerd/continuity/fs/copy_linux.go
new file mode 100644
index 000000000..81c71522a
--- /dev/null
+++ b/vendor/github.com/containerd/continuity/fs/copy_linux.go
@@ -0,0 +1,144 @@
+/*
+   Copyright The containerd Authors.
+
+   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.
+*/
+
+package fs
+
+import (
+	"io"
+	"os"
+	"syscall"
+
+	"github.com/containerd/continuity/sysx"
+	"github.com/pkg/errors"
+	"golang.org/x/sys/unix"
+)
+
+func copyFileInfo(fi os.FileInfo, name string) error {
+	st := fi.Sys().(*syscall.Stat_t)
+	if err := os.Lchown(name, int(st.Uid), int(st.Gid)); err != nil {
+		if os.IsPermission(err) {
+			// Normally if uid/gid are the same this would be a no-op, but some
+			// filesystems may still return EPERM... for instance NFS does this.
+			// In such a case, this is not an error.
+			if dstStat, err2 := os.Lstat(name); err2 == nil {
+				st2 := dstStat.Sys().(*syscall.Stat_t)
+				if st.Uid == st2.Uid && st.Gid == st2.Gid {
+					err = nil
+				}
+			}
+		}
+		if err != nil {
+			return errors.Wrapf(err, "failed to chown %s", name)
+		}
+	}
+
+	if (fi.Mode() & os.ModeSymlink) != os.ModeSymlink {
+		if err := os.Chmod(name, fi.Mode()); err != nil {
+			return errors.Wrapf(err, "failed to chmod %s", name)
+		}
+	}
+
+	timespec := []unix.Timespec{unix.Timespec(StatAtime(st)), unix.Timespec(StatMtime(st))}
+	if err := unix.UtimesNanoAt(unix.AT_FDCWD, name, timespec, unix.AT_SYMLINK_NOFOLLOW); err != nil {
+		return errors.Wrapf(err, "failed to utime %s", name)
+	}
+
+	return nil
+}
+
+const maxSSizeT = int64(^uint(0) >> 1)
+
+func copyFileContent(dst, src *os.File) error {
+	st, err := src.Stat()
+	if err != nil {
+		return errors.Wrap(err, "unable to stat source")
+	}
+
+	size := st.Size()
+	first := true
+	srcFd := int(src.Fd())
+	dstFd := int(dst.Fd())
+
+	for size > 0 {
+		// Ensure that we are never trying to copy more than SSIZE_MAX at a
+		// time and at the same time avoids overflows when the file is larger
+		// than 4GB on 32-bit systems.
+		var copySize int
+		if size > maxSSizeT {
+			copySize = int(maxSSizeT)
+		} else {
+			copySize = int(size)
+		}
+		n, err := unix.CopyFileRange(srcFd, nil, dstFd, nil, copySize, 0)
+		if err != nil {
+			if (err != unix.ENOSYS && err != unix.EXDEV) || !first {
+				return errors.Wrap(err, "copy file range failed")
+			}
+
+			buf := bufferPool.Get().(*[]byte)
+			_, err = io.CopyBuffer(dst, src, *buf)
+			bufferPool.Put(buf)
+			return errors.Wrap(err, "userspace copy failed")
+		}
+
+		first = false
+		size -= int64(n)
+	}
+
+	return nil
+}
+
+func copyXAttrs(dst, src string, xeh XAttrErrorHandler) error {
+	xattrKeys, err := sysx.LListxattr(src)
+	if err != nil {
+		e := errors.Wrapf(err, "failed to list xattrs on %s", src)
+		if xeh != nil {
+			e = xeh(dst, src, "", e)
+		}
+		return e
+	}
+	for _, xattr := range xattrKeys {
+		data, err := sysx.LGetxattr(src, xattr)
+		if err != nil {
+			e := errors.Wrapf(err, "failed to get xattr %q on %s", xattr, src)
+			if xeh != nil {
+				if e = xeh(dst, src, xattr, e); e == nil {
+					continue
+				}
+			}
+			return e
+		}
+		if err := sysx.LSetxattr(dst, xattr, data, 0); err != nil {
+			e := errors.Wrapf(err, "failed to set xattr %q on %s", xattr, dst)
+			if xeh != nil {
+				if e = xeh(dst, src, xattr, e); e == nil {
+					continue
+				}
+			}
+			return e
+		}
+	}
+
+	return nil
+}
+
+func copyDevice(dst string, fi os.FileInfo) error {
+	st, ok := fi.Sys().(*syscall.Stat_t)
+	if !ok {
+		return errors.New("unsupported stat type")
+	}
+	return unix.Mknod(dst, uint32(fi.Mode()), int(st.Rdev))
+}
diff --git a/vendor/github.com/containerd/continuity/fs/copy_unix.go b/vendor/github.com/containerd/continuity/fs/copy_unix.go
new file mode 100644
index 000000000..73c01a46d
--- /dev/null
+++ b/vendor/github.com/containerd/continuity/fs/copy_unix.go
@@ -0,0 +1,112 @@
+// +build solaris darwin freebsd
+
+/*
+   Copyright The containerd Authors.
+
+   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.
+*/
+
+package fs
+
+import (
+	"io"
+	"os"
+	"syscall"
+
+	"github.com/containerd/continuity/sysx"
+	"github.com/pkg/errors"
+	"golang.org/x/sys/unix"
+)
+
+func copyFileInfo(fi os.FileInfo, name string) error {
+	st := fi.Sys().(*syscall.Stat_t)
+	if err := os.Lchown(name, int(st.Uid), int(st.Gid)); err != nil {
+		if os.IsPermission(err) {
+			// Normally if uid/gid are the same this would be a no-op, but some
+			// filesystems may still return EPERM... for instance NFS does this.
+			// In such a case, this is not an error.
+			if dstStat, err2 := os.Lstat(name); err2 == nil {
+				st2 := dstStat.Sys().(*syscall.Stat_t)
+				if st.Uid == st2.Uid && st.Gid == st2.Gid {
+					err = nil
+				}
+			}
+		}
+		if err != nil {
+			return errors.Wrapf(err, "failed to chown %s", name)
+		}
+	}
+
+	if (fi.Mode() & os.ModeSymlink) != os.ModeSymlink {
+		if err := os.Chmod(name, fi.Mode()); err != nil {
+			return errors.Wrapf(err, "failed to chmod %s", name)
+		}
+	}
+
+	timespec := []syscall.Timespec{StatAtime(st), StatMtime(st)}
+	if err := syscall.UtimesNano(name, timespec); err != nil {
+		return errors.Wrapf(err, "failed to utime %s", name)
+	}
+
+	return nil
+}
+
+func copyFileContent(dst, src *os.File) error {
+	buf := bufferPool.Get().(*[]byte)
+	_, err := io.CopyBuffer(dst, src, *buf)
+	bufferPool.Put(buf)
+
+	return err
+}
+
+func copyXAttrs(dst, src string, xeh XAttrErrorHandler) error {
+	xattrKeys, err := sysx.LListxattr(src)
+	if err != nil {
+		e := errors.Wrapf(err, "failed to list xattrs on %s", src)
+		if xeh != nil {
+			e = xeh(dst, src, "", e)
+		}
+		return e
+	}
+	for _, xattr := range xattrKeys {
+		data, err := sysx.LGetxattr(src, xattr)
+		if err != nil {
+			e := errors.Wrapf(err, "failed to get xattr %q on %s", xattr, src)
+			if xeh != nil {
+				if e = xeh(dst, src, xattr, e); e == nil {
+					continue
+				}
+			}
+			return e
+		}
+		if err := sysx.LSetxattr(dst, xattr, data, 0); err != nil {
+			e := errors.Wrapf(err, "failed to set xattr %q on %s", xattr, dst)
+			if xeh != nil {
+				if e = xeh(dst, src, xattr, e); e == nil {
+					continue
+				}
+			}
+			return e
+		}
+	}
+
+	return nil
+}
+
+func copyDevice(dst string, fi os.FileInfo) error {
+	st, ok := fi.Sys().(*syscall.Stat_t)
+	if !ok {
+		return errors.New("unsupported stat type")
+	}
+	return unix.Mknod(dst, uint32(fi.Mode()), int(st.Rdev))
+}
diff --git a/vendor/github.com/containerd/continuity/fs/copy_windows.go b/vendor/github.com/containerd/continuity/fs/copy_windows.go
new file mode 100644
index 000000000..27c7d7dbb
--- /dev/null
+++ b/vendor/github.com/containerd/continuity/fs/copy_windows.go
@@ -0,0 +1,49 @@
+/*
+   Copyright The containerd Authors.
+
+   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.
+*/
+
+package fs
+
+import (
+	"io"
+	"os"
+
+	"github.com/pkg/errors"
+)
+
+func copyFileInfo(fi os.FileInfo, name string) error {
+	if err := os.Chmod(name, fi.Mode()); err != nil {
+		return errors.Wrapf(err, "failed to chmod %s", name)
+	}
+
+	// TODO: copy windows specific metadata
+
+	return nil
+}
+
+func copyFileContent(dst, src *os.File) error {
+	buf := bufferPool.Get().(*[]byte)
+	_, err := io.CopyBuffer(dst, src, *buf)
+	bufferPool.Put(buf)
+	return err
+}
+
+func copyXAttrs(dst, src string, xeh XAttrErrorHandler) error {
+	return nil
+}
+
+func copyDevice(dst string, fi os.FileInfo) error {
+	return errors.New("device copy not supported")
+}
diff --git a/vendor/github.com/containerd/continuity/fs/diff.go b/vendor/github.com/containerd/continuity/fs/diff.go
new file mode 100644
index 000000000..e64f9e73d
--- /dev/null
+++ b/vendor/github.com/containerd/continuity/fs/diff.go
@@ -0,0 +1,326 @@
+/*
+   Copyright The containerd Authors.
+
+   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.
+*/
+
+package fs
+
+import (
+	"context"
+	"os"
+	"path/filepath"
+	"strings"
+
+	"golang.org/x/sync/errgroup"
+
+	"github.com/sirupsen/logrus"
+)
+
+// ChangeKind is the type of modification that
+// a change is making.
+type ChangeKind int
+
+const (
+	// ChangeKindUnmodified represents an unmodified
+	// file
+	ChangeKindUnmodified = iota
+
+	// ChangeKindAdd represents an addition of
+	// a file
+	ChangeKindAdd
+
+	// ChangeKindModify represents a change to
+	// an existing file
+	ChangeKindModify
+
+	// ChangeKindDelete represents a delete of
+	// a file
+	ChangeKindDelete
+)
+
+func (k ChangeKind) String() string {
+	switch k {
+	case ChangeKindUnmodified:
+		return "unmodified"
+	case ChangeKindAdd:
+		return "add"
+	case ChangeKindModify:
+		return "modify"
+	case ChangeKindDelete:
+		return "delete"
+	default:
+		return ""
+	}
+}
+
+// Change represents single change between a diff and its parent.
+type Change struct {
+	Kind ChangeKind
+	Path string
+}
+
+// ChangeFunc is the type of function called for each change
+// computed during a directory changes calculation.
+type ChangeFunc func(ChangeKind, string, os.FileInfo, error) error
+
+// Changes computes changes between two directories calling the
+// given change function for each computed change. The first
+// directory is intended to the base directory and second
+// directory the changed directory.
+//
+// The change callback is called by the order of path names and
+// should be appliable in that order.
+//  Due to this apply ordering, the following is true
+//  - Removed directory trees only create a single change for the root
+//    directory removed. Remaining changes are implied.
+//  - A directory which is modified to become a file will not have
+//    delete entries for sub-path items, their removal is implied
+//    by the removal of the parent directory.
+//
+// Opaque directories will not be treated specially and each file
+// removed from the base directory will show up as a removal.
+//
+// File content comparisons will be done on files which have timestamps
+// which may have been truncated. If either of the files being compared
+// has a zero value nanosecond value, each byte will be compared for
+// differences. If 2 files have the same seconds value but different
+// nanosecond values where one of those values is zero, the files will
+// be considered unchanged if the content is the same. This behavior
+// is to account for timestamp truncation during archiving.
+func Changes(ctx context.Context, a, b string, changeFn ChangeFunc) error {
+	if a == "" {
+		logrus.Debugf("Using single walk diff for %s", b)
+		return addDirChanges(ctx, changeFn, b)
+	} else if diffOptions := detectDirDiff(b, a); diffOptions != nil {
+		logrus.Debugf("Using single walk diff for %s from %s", diffOptions.diffDir, a)
+		return diffDirChanges(ctx, changeFn, a, diffOptions)
+	}
+
+	logrus.Debugf("Using double walk diff for %s from %s", b, a)
+	return doubleWalkDiff(ctx, changeFn, a, b)
+}
+
+func addDirChanges(ctx context.Context, changeFn ChangeFunc, root string) error {
+	return filepath.Walk(root, func(path string, f os.FileInfo, err error) error {
+		if err != nil {
+			return err
+		}
+
+		// Rebase path
+		path, err = filepath.Rel(root, path)
+		if err != nil {
+			return err
+		}
+
+		path = filepath.Join(string(os.PathSeparator), path)
+
+		// Skip root
+		if path == string(os.PathSeparator) {
+			return nil
+		}
+
+		return changeFn(ChangeKindAdd, path, f, nil)
+	})
+}
+
+// diffDirOptions is used when the diff can be directly calculated from
+// a diff directory to its base, without walking both trees.
+type diffDirOptions struct {
+	diffDir      string
+	skipChange   func(string) (bool, error)
+	deleteChange func(string, string, os.FileInfo) (string, error)
+}
+
+// diffDirChanges walks the diff directory and compares changes against the base.
+func diffDirChanges(ctx context.Context, changeFn ChangeFunc, base string, o *diffDirOptions) error {
+	changedDirs := make(map[string]struct{})
+	return filepath.Walk(o.diffDir, func(path string, f os.FileInfo, err error) error {
+		if err != nil {
+			return err
+		}
+
+		// Rebase path
+		path, err = filepath.Rel(o.diffDir, path)
+		if err != nil {
+			return err
+		}
+
+		path = filepath.Join(string(os.PathSeparator), path)
+
+		// Skip root
+		if path == string(os.PathSeparator) {
+			return nil
+		}
+
+		// TODO: handle opaqueness, start new double walker at this
+		// location to get deletes, and skip tree in single walker
+
+		if o.skipChange != nil {
+			if skip, err := o.skipChange(path); skip {
+				return err
+			}
+		}
+
+		var kind ChangeKind
+
+		deletedFile, err := o.deleteChange(o.diffDir, path, f)
+		if err != nil {
+			return err
+		}
+
+		// Find out what kind of modification happened
+		if deletedFile != "" {
+			path = deletedFile
+			kind = ChangeKindDelete
+			f = nil
+		} else {
+			// Otherwise, the file was added
+			kind = ChangeKindAdd
+
+			// ...Unless it already existed in a base, in which case, it's a modification
+			stat, err := os.Stat(filepath.Join(base, path))
+			if err != nil && !os.IsNotExist(err) {
+				return err
+			}
+			if err == nil {
+				// The file existed in the base, so that's a modification
+
+				// However, if it's a directory, maybe it wasn't actually modified.
+				// If you modify /foo/bar/baz, then /foo will be part of the changed files only because it's the parent of bar
+				if stat.IsDir() && f.IsDir() {
+					if f.Size() == stat.Size() && f.Mode() == stat.Mode() && sameFsTime(f.ModTime(), stat.ModTime()) {
+						// Both directories are the same, don't record the change
+						return nil
+					}
+				}
+				kind = ChangeKindModify
+			}
+		}
+
+		// If /foo/bar/file.txt is modified, then /foo/bar must be part of the changed files.
+		// This block is here to ensure the change is recorded even if the
+		// modify time, mode and size of the parent directory in the rw and ro layers are all equal.
+		// Check https://github.com/docker/docker/pull/13590 for details.
+		if f.IsDir() {
+			changedDirs[path] = struct{}{}
+		}
+		if kind == ChangeKindAdd || kind == ChangeKindDelete {
+			parent := filepath.Dir(path)
+			if _, ok := changedDirs[parent]; !ok && parent != "/" {
+				pi, err := os.Stat(filepath.Join(o.diffDir, parent))
+				if err := changeFn(ChangeKindModify, parent, pi, err); err != nil {
+					return err
+				}
+				changedDirs[parent] = struct{}{}
+			}
+		}
+
+		return changeFn(kind, path, f, nil)
+	})
+}
+
+// doubleWalkDiff walks both directories to create a diff
+func doubleWalkDiff(ctx context.Context, changeFn ChangeFunc, a, b string) (err error) {
+	g, ctx := errgroup.WithContext(ctx)
+
+	var (
+		c1 = make(chan *currentPath)
+		c2 = make(chan *currentPath)
+
+		f1, f2 *currentPath
+		rmdir  string
+	)
+	g.Go(func() error {
+		defer close(c1)
+		return pathWalk(ctx, a, c1)
+	})
+	g.Go(func() error {
+		defer close(c2)
+		return pathWalk(ctx, b, c2)
+	})
+	g.Go(func() error {
+		for c1 != nil || c2 != nil {
+			if f1 == nil && c1 != nil {
+				f1, err = nextPath(ctx, c1)
+				if err != nil {
+					return err
+				}
+				if f1 == nil {
+					c1 = nil
+				}
+			}
+
+			if f2 == nil && c2 != nil {
+				f2, err = nextPath(ctx, c2)
+				if err != nil {
+					return err
+				}
+				if f2 == nil {
+					c2 = nil
+				}
+			}
+			if f1 == nil && f2 == nil {
+				continue
+			}
+
+			var f os.FileInfo
+			k, p := pathChange(f1, f2)
+			switch k {
+			case ChangeKindAdd:
+				if rmdir != "" {
+					rmdir = ""
+				}
+				f = f2.f
+				f2 = nil
+			case ChangeKindDelete:
+				// Check if this file is already removed by being
+				// under of a removed directory
+				if rmdir != "" && strings.HasPrefix(f1.path, rmdir) {
+					f1 = nil
+					continue
+				} else if f1.f.IsDir() {
+					rmdir = f1.path + string(os.PathSeparator)
+				} else if rmdir != "" {
+					rmdir = ""
+				}
+				f1 = nil
+			case ChangeKindModify:
+				same, err := sameFile(f1, f2)
+				if err != nil {
+					return err
+				}
+				if f1.f.IsDir() && !f2.f.IsDir() {
+					rmdir = f1.path + string(os.PathSeparator)
+				} else if rmdir != "" {
+					rmdir = ""
+				}
+				f = f2.f
+				f1 = nil
+				f2 = nil
+				if same {
+					if !isLinked(f) {
+						continue
+					}
+					k = ChangeKindUnmodified
+				}
+			}
+			if err := changeFn(k, p, f, nil); err != nil {
+				return err
+			}
+		}
+		return nil
+	})
+
+	return g.Wait()
+}
diff --git a/vendor/github.com/containerd/continuity/fs/diff_unix.go b/vendor/github.com/containerd/continuity/fs/diff_unix.go
new file mode 100644
index 000000000..7913af27d
--- /dev/null
+++ b/vendor/github.com/containerd/continuity/fs/diff_unix.go
@@ -0,0 +1,74 @@
+// +build !windows
+
+/*
+   Copyright The containerd Authors.
+
+   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.
+*/
+
+package fs
+
+import (
+	"bytes"
+	"os"
+	"syscall"
+
+	"github.com/containerd/continuity/sysx"
+	"github.com/pkg/errors"
+)
+
+// detectDirDiff returns diff dir options if a directory could
+// be found in the mount info for upper which is the direct
+// diff with the provided lower directory
+func detectDirDiff(upper, lower string) *diffDirOptions {
+	// TODO: get mount options for upper
+	// TODO: detect AUFS
+	// TODO: detect overlay
+	return nil
+}
+
+// compareSysStat returns whether the stats are equivalent,
+// whether the files are considered the same file, and
+// an error
+func compareSysStat(s1, s2 interface{}) (bool, error) {
+	ls1, ok := s1.(*syscall.Stat_t)
+	if !ok {
+		return false, nil
+	}
+	ls2, ok := s2.(*syscall.Stat_t)
+	if !ok {
+		return false, nil
+	}
+
+	return ls1.Mode == ls2.Mode && ls1.Uid == ls2.Uid && ls1.Gid == ls2.Gid && ls1.Rdev == ls2.Rdev, nil
+}
+
+func compareCapabilities(p1, p2 string) (bool, error) {
+	c1, err := sysx.LGetxattr(p1, "security.capability")
+	if err != nil && err != sysx.ENODATA {
+		return false, errors.Wrapf(err, "failed to get xattr for %s", p1)
+	}
+	c2, err := sysx.LGetxattr(p2, "security.capability")
+	if err != nil && err != sysx.ENODATA {
+		return false, errors.Wrapf(err, "failed to get xattr for %s", p2)
+	}
+	return bytes.Equal(c1, c2), nil
+}
+
+func isLinked(f os.FileInfo) bool {
+	s, ok := f.Sys().(*syscall.Stat_t)
+	if !ok {
+		return false
+	}
+	return !f.IsDir() && s.Nlink > 1
+}
diff --git a/vendor/github.com/containerd/continuity/fs/diff_windows.go b/vendor/github.com/containerd/continuity/fs/diff_windows.go
new file mode 100644
index 000000000..4bfa72d3a
--- /dev/null
+++ b/vendor/github.com/containerd/continuity/fs/diff_windows.go
@@ -0,0 +1,48 @@
+/*
+   Copyright The containerd Authors.
+
+   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.
+*/
+
+package fs
+
+import (
+	"os"
+
+	"golang.org/x/sys/windows"
+)
+
+func detectDirDiff(upper, lower string) *diffDirOptions {
+	return nil
+}
+
+func compareSysStat(s1, s2 interface{}) (bool, error) {
+	f1, ok := s1.(windows.Win32FileAttributeData)
+	if !ok {
+		return false, nil
+	}
+	f2, ok := s2.(windows.Win32FileAttributeData)
+	if !ok {
+		return false, nil
+	}
+	return f1.FileAttributes == f2.FileAttributes, nil
+}
+
+func compareCapabilities(p1, p2 string) (bool, error) {
+	// TODO: Use windows equivalent
+	return true, nil
+}
+
+func isLinked(os.FileInfo) bool {
+	return false
+}
diff --git a/vendor/github.com/containerd/continuity/fs/dtype_linux.go b/vendor/github.com/containerd/continuity/fs/dtype_linux.go
new file mode 100644
index 000000000..10510d8de
--- /dev/null
+++ b/vendor/github.com/containerd/continuity/fs/dtype_linux.go
@@ -0,0 +1,103 @@
+// +build linux
+
+/*
+   Copyright The containerd Authors.
+
+   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.
+*/
+
+package fs
+
+import (
+	"fmt"
+	"io/ioutil"
+	"os"
+	"syscall"
+	"unsafe"
+)
+
+func locateDummyIfEmpty(path string) (string, error) {
+	children, err := ioutil.ReadDir(path)
+	if err != nil {
+		return "", err
+	}
+	if len(children) != 0 {
+		return "", nil
+	}
+	dummyFile, err := ioutil.TempFile(path, "fsutils-dummy")
+	if err != nil {
+		return "", err
+	}
+	name := dummyFile.Name()
+	err = dummyFile.Close()
+	return name, err
+}
+
+// SupportsDType returns whether the filesystem mounted on path supports d_type
+func SupportsDType(path string) (bool, error) {
+	// locate dummy so that we have at least one dirent
+	dummy, err := locateDummyIfEmpty(path)
+	if err != nil {
+		return false, err
+	}
+	if dummy != "" {
+		defer os.Remove(dummy)
+	}
+
+	visited := 0
+	supportsDType := true
+	fn := func(ent *syscall.Dirent) bool {
+		visited++
+		if ent.Type == syscall.DT_UNKNOWN {
+			supportsDType = false
+			// stop iteration
+			return true
+		}
+		// continue iteration
+		return false
+	}
+	if err = iterateReadDir(path, fn); err != nil {
+		return false, err
+	}
+	if visited == 0 {
+		return false, fmt.Errorf("did not hit any dirent during iteration %s", path)
+	}
+	return supportsDType, nil
+}
+
+func iterateReadDir(path string, fn func(*syscall.Dirent) bool) error {
+	d, err := os.Open(path)
+	if err != nil {
+		return err
+	}
+	defer d.Close()
+	fd := int(d.Fd())
+	buf := make([]byte, 4096)
+	for {
+		nbytes, err := syscall.ReadDirent(fd, buf)
+		if err != nil {
+			return err
+		}
+		if nbytes == 0 {
+			break
+		}
+		for off := 0; off < nbytes; {
+			ent := (*syscall.Dirent)(unsafe.Pointer(&buf[off]))
+			if stop := fn(ent); stop {
+				return nil
+			}
+			off += int(ent.Reclen)
+		}
+	}
+	return nil
+}
diff --git a/vendor/github.com/containerd/continuity/fs/du.go b/vendor/github.com/containerd/continuity/fs/du.go
new file mode 100644
index 000000000..fccc985dc
--- /dev/null
+++ b/vendor/github.com/containerd/continuity/fs/du.go
@@ -0,0 +1,38 @@
+/*
+   Copyright The containerd Authors.
+
+   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.
+*/
+
+package fs
+
+import "context"
+
+// Usage of disk information
+type Usage struct {
+	Inodes int64
+	Size   int64
+}
+
+// DiskUsage counts the number of inodes and disk usage for the resources under
+// path.
+func DiskUsage(ctx context.Context, roots ...string) (Usage, error) {
+	return diskUsage(ctx, roots...)
+}
+
+// DiffUsage counts the numbers of inodes and disk usage in the
+// diff between the 2 directories. The first path is intended
+// as the base directory and the second as the changed directory.
+func DiffUsage(ctx context.Context, a, b string) (Usage, error) {
+	return diffUsage(ctx, a, b)
+}
diff --git a/vendor/github.com/containerd/continuity/fs/du_unix.go b/vendor/github.com/containerd/continuity/fs/du_unix.go
new file mode 100644
index 000000000..e22ffbea3
--- /dev/null
+++ b/vendor/github.com/containerd/continuity/fs/du_unix.go
@@ -0,0 +1,110 @@
+// +build !windows
+
+/*
+   Copyright The containerd Authors.
+
+   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.
+*/
+
+package fs
+
+import (
+	"context"
+	"os"
+	"path/filepath"
+	"syscall"
+)
+
+type inode struct {
+	// TODO(stevvooe): Can probably reduce memory usage by not tracking
+	// device, but we can leave this right for now.
+	dev, ino uint64
+}
+
+func newInode(stat *syscall.Stat_t) inode {
+	return inode{
+		// Dev is uint32 on darwin/bsd, uint64 on linux/solaris
+		dev: uint64(stat.Dev), // nolint: unconvert
+		// Ino is uint32 on bsd, uint64 on darwin/linux/solaris
+		ino: uint64(stat.Ino), // nolint: unconvert
+	}
+}
+
+func diskUsage(ctx context.Context, roots ...string) (Usage, error) {
+
+	var (
+		size   int64
+		inodes = map[inode]struct{}{} // expensive!
+	)
+
+	for _, root := range roots {
+		if err := filepath.Walk(root, func(path string, fi os.FileInfo, err error) error {
+			if err != nil {
+				return err
+			}
+
+			select {
+			case <-ctx.Done():
+				return ctx.Err()
+			default:
+			}
+
+			inoKey := newInode(fi.Sys().(*syscall.Stat_t))
+			if _, ok := inodes[inoKey]; !ok {
+				inodes[inoKey] = struct{}{}
+				size += fi.Size()
+			}
+
+			return nil
+		}); err != nil {
+			return Usage{}, err
+		}
+	}
+
+	return Usage{
+		Inodes: int64(len(inodes)),
+		Size:   size,
+	}, nil
+}
+
+func diffUsage(ctx context.Context, a, b string) (Usage, error) {
+	var (
+		size   int64
+		inodes = map[inode]struct{}{} // expensive!
+	)
+
+	if err := Changes(ctx, a, b, func(kind ChangeKind, _ string, fi os.FileInfo, err error) error {
+		if err != nil {
+			return err
+		}
+
+		if kind == ChangeKindAdd || kind == ChangeKindModify {
+			inoKey := newInode(fi.Sys().(*syscall.Stat_t))
+			if _, ok := inodes[inoKey]; !ok {
+				inodes[inoKey] = struct{}{}
+				size += fi.Size()
+			}
+
+			return nil
+
+		}
+		return nil
+	}); err != nil {
+		return Usage{}, err
+	}
+
+	return Usage{
+		Inodes: int64(len(inodes)),
+		Size:   size,
+	}, nil
+}
diff --git a/vendor/github.com/containerd/continuity/fs/du_windows.go b/vendor/github.com/containerd/continuity/fs/du_windows.go
new file mode 100644
index 000000000..8f25ec59c
--- /dev/null
+++ b/vendor/github.com/containerd/continuity/fs/du_windows.go
@@ -0,0 +1,82 @@
+// +build windows
+
+/*
+   Copyright The containerd Authors.
+
+   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.
+*/
+
+package fs
+
+import (
+	"context"
+	"os"
+	"path/filepath"
+)
+
+func diskUsage(ctx context.Context, roots ...string) (Usage, error) {
+	var (
+		size int64
+	)
+
+	// TODO(stevvooe): Support inodes (or equivalent) for windows.
+
+	for _, root := range roots {
+		if err := filepath.Walk(root, func(path string, fi os.FileInfo, err error) error {
+			if err != nil {
+				return err
+			}
+
+			select {
+			case <-ctx.Done():
+				return ctx.Err()
+			default:
+			}
+
+			size += fi.Size()
+			return nil
+		}); err != nil {
+			return Usage{}, err
+		}
+	}
+
+	return Usage{
+		Size: size,
+	}, nil
+}
+
+func diffUsage(ctx context.Context, a, b string) (Usage, error) {
+	var (
+		size int64
+	)
+
+	if err := Changes(ctx, a, b, func(kind ChangeKind, _ string, fi os.FileInfo, err error) error {
+		if err != nil {
+			return err
+		}
+
+		if kind == ChangeKindAdd || kind == ChangeKindModify {
+			size += fi.Size()
+
+			return nil
+
+		}
+		return nil
+	}); err != nil {
+		return Usage{}, err
+	}
+
+	return Usage{
+		Size: size,
+	}, nil
+}
diff --git a/vendor/github.com/containerd/continuity/fs/hardlink.go b/vendor/github.com/containerd/continuity/fs/hardlink.go
new file mode 100644
index 000000000..762aa45e6
--- /dev/null
+++ b/vendor/github.com/containerd/continuity/fs/hardlink.go
@@ -0,0 +1,43 @@
+/*
+   Copyright The containerd Authors.
+
+   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.
+*/
+
+package fs
+
+import "os"
+
+// GetLinkInfo returns an identifier representing the node a hardlink is pointing
+// to. If the file is not hard linked then 0 will be returned.
+func GetLinkInfo(fi os.FileInfo) (uint64, bool) {
+	return getLinkInfo(fi)
+}
+
+// getLinkSource returns a path for the given name and
+// file info to its link source in the provided inode
+// map. If the given file name is not in the map and
+// has other links, it is added to the inode map
+// to be a source for other link locations.
+func getLinkSource(name string, fi os.FileInfo, inodes map[uint64]string) (string, error) {
+	inode, isHardlink := getLinkInfo(fi)
+	if !isHardlink {
+		return "", nil
+	}
+
+	path, ok := inodes[inode]
+	if !ok {
+		inodes[inode] = name
+	}
+	return path, nil
+}
diff --git a/vendor/github.com/containerd/continuity/fs/hardlink_unix.go b/vendor/github.com/containerd/continuity/fs/hardlink_unix.go
new file mode 100644
index 000000000..f95f0904c
--- /dev/null
+++ b/vendor/github.com/containerd/continuity/fs/hardlink_unix.go
@@ -0,0 +1,34 @@
+// +build !windows
+
+/*
+   Copyright The containerd Authors.
+
+   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.
+*/
+
+package fs
+
+import (
+	"os"
+	"syscall"
+)
+
+func getLinkInfo(fi os.FileInfo) (uint64, bool) {
+	s, ok := fi.Sys().(*syscall.Stat_t)
+	if !ok {
+		return 0, false
+	}
+
+	// Ino is uint32 on bsd, uint64 on darwin/linux/solaris
+	return uint64(s.Ino), !fi.IsDir() && s.Nlink > 1 // nolint: unconvert
+}
diff --git a/vendor/github.com/containerd/continuity/fs/hardlink_windows.go b/vendor/github.com/containerd/continuity/fs/hardlink_windows.go
new file mode 100644
index 000000000..748554714
--- /dev/null
+++ b/vendor/github.com/containerd/continuity/fs/hardlink_windows.go
@@ -0,0 +1,23 @@
+/*
+   Copyright The containerd Authors.
+
+   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.
+*/
+
+package fs
+
+import "os"
+
+func getLinkInfo(fi os.FileInfo) (uint64, bool) {
+	return 0, false
+}
diff --git a/vendor/github.com/containerd/continuity/fs/path.go b/vendor/github.com/containerd/continuity/fs/path.go
new file mode 100644
index 000000000..8863caa9d
--- /dev/null
+++ b/vendor/github.com/containerd/continuity/fs/path.go
@@ -0,0 +1,313 @@
+/*
+   Copyright The containerd Authors.
+
+   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.
+*/
+
+package fs
+
+import (
+	"bytes"
+	"context"
+	"io"
+	"os"
+	"path/filepath"
+
+	"github.com/pkg/errors"
+)
+
+var (
+	errTooManyLinks = errors.New("too many links")
+)
+
+type currentPath struct {
+	path     string
+	f        os.FileInfo
+	fullPath string
+}
+
+func pathChange(lower, upper *currentPath) (ChangeKind, string) {
+	if lower == nil {
+		if upper == nil {
+			panic("cannot compare nil paths")
+		}
+		return ChangeKindAdd, upper.path
+	}
+	if upper == nil {
+		return ChangeKindDelete, lower.path
+	}
+
+	switch i := directoryCompare(lower.path, upper.path); {
+	case i < 0:
+		// File in lower that is not in upper
+		return ChangeKindDelete, lower.path
+	case i > 0:
+		// File in upper that is not in lower
+		return ChangeKindAdd, upper.path
+	default:
+		return ChangeKindModify, upper.path
+	}
+}
+
+func directoryCompare(a, b string) int {
+	l := len(a)
+	if len(b) < l {
+		l = len(b)
+	}
+	for i := 0; i < l; i++ {
+		c1, c2 := a[i], b[i]
+		if c1 == filepath.Separator {
+			c1 = byte(0)
+		}
+		if c2 == filepath.Separator {
+			c2 = byte(0)
+		}
+		if c1 < c2 {
+			return -1
+		}
+		if c1 > c2 {
+			return +1
+		}
+	}
+	if len(a) < len(b) {
+		return -1
+	}
+	if len(a) > len(b) {
+		return +1
+	}
+	return 0
+}
+
+func sameFile(f1, f2 *currentPath) (bool, error) {
+	if os.SameFile(f1.f, f2.f) {
+		return true, nil
+	}
+
+	equalStat, err := compareSysStat(f1.f.Sys(), f2.f.Sys())
+	if err != nil || !equalStat {
+		return equalStat, err
+	}
+
+	if eq, err := compareCapabilities(f1.fullPath, f2.fullPath); err != nil || !eq {
+		return eq, err
+	}
+
+	// If not a directory also check size, modtime, and content
+	if !f1.f.IsDir() {
+		if f1.f.Size() != f2.f.Size() {
+			return false, nil
+		}
+		t1 := f1.f.ModTime()
+		t2 := f2.f.ModTime()
+
+		if t1.Unix() != t2.Unix() {
+			return false, nil
+		}
+
+		// If the timestamp may have been truncated in both of the
+		// files, check content of file to determine difference
+		if t1.Nanosecond() == 0 && t2.Nanosecond() == 0 {
+			var eq bool
+			if (f1.f.Mode() & os.ModeSymlink) == os.ModeSymlink {
+				eq, err = compareSymlinkTarget(f1.fullPath, f2.fullPath)
+			} else if f1.f.Size() > 0 {
+				eq, err = compareFileContent(f1.fullPath, f2.fullPath)
+			}
+			if err != nil || !eq {
+				return eq, err
+			}
+		} else if t1.Nanosecond() != t2.Nanosecond() {
+			return false, nil
+		}
+	}
+
+	return true, nil
+}
+
+func compareSymlinkTarget(p1, p2 string) (bool, error) {
+	t1, err := os.Readlink(p1)
+	if err != nil {
+		return false, err
+	}
+	t2, err := os.Readlink(p2)
+	if err != nil {
+		return false, err
+	}
+	return t1 == t2, nil
+}
+
+const compareChuckSize = 32 * 1024
+
+// compareFileContent compares the content of 2 same sized files
+// by comparing each byte.
+func compareFileContent(p1, p2 string) (bool, error) {
+	f1, err := os.Open(p1)
+	if err != nil {
+		return false, err
+	}
+	defer f1.Close()
+	f2, err := os.Open(p2)
+	if err != nil {
+		return false, err
+	}
+	defer f2.Close()
+
+	b1 := make([]byte, compareChuckSize)
+	b2 := make([]byte, compareChuckSize)
+	for {
+		n1, err1 := f1.Read(b1)
+		if err1 != nil && err1 != io.EOF {
+			return false, err1
+		}
+		n2, err2 := f2.Read(b2)
+		if err2 != nil && err2 != io.EOF {
+			return false, err2
+		}
+		if n1 != n2 || !bytes.Equal(b1[:n1], b2[:n2]) {
+			return false, nil
+		}
+		if err1 == io.EOF && err2 == io.EOF {
+			return true, nil
+		}
+	}
+}
+
+func pathWalk(ctx context.Context, root string, pathC chan<- *currentPath) error {
+	return filepath.Walk(root, func(path string, f os.FileInfo, err error) error {
+		if err != nil {
+			return err
+		}
+
+		// Rebase path
+		path, err = filepath.Rel(root, path)
+		if err != nil {
+			return err
+		}
+
+		path = filepath.Join(string(os.PathSeparator), path)
+
+		// Skip root
+		if path == string(os.PathSeparator) {
+			return nil
+		}
+
+		p := &currentPath{
+			path:     path,
+			f:        f,
+			fullPath: filepath.Join(root, path),
+		}
+
+		select {
+		case <-ctx.Done():
+			return ctx.Err()
+		case pathC <- p:
+			return nil
+		}
+	})
+}
+
+func nextPath(ctx context.Context, pathC <-chan *currentPath) (*currentPath, error) {
+	select {
+	case <-ctx.Done():
+		return nil, ctx.Err()
+	case p := <-pathC:
+		return p, nil
+	}
+}
+
+// RootPath joins a path with a root, evaluating and bounding any
+// symlink to the root directory.
+func RootPath(root, path string) (string, error) {
+	if path == "" {
+		return root, nil
+	}
+	var linksWalked int // to protect against cycles
+	for {
+		i := linksWalked
+		newpath, err := walkLinks(root, path, &linksWalked)
+		if err != nil {
+			return "", err
+		}
+		path = newpath
+		if i == linksWalked {
+			newpath = filepath.Join("/", newpath)
+			if path == newpath {
+				return filepath.Join(root, newpath), nil
+			}
+			path = newpath
+		}
+	}
+}
+
+func walkLink(root, path string, linksWalked *int) (newpath string, islink bool, err error) {
+	if *linksWalked > 255 {
+		return "", false, errTooManyLinks
+	}
+
+	path = filepath.Join("/", path)
+	if path == "/" {
+		return path, false, nil
+	}
+	realPath := filepath.Join(root, path)
+
+	fi, err := os.Lstat(realPath)
+	if err != nil {
+		// If path does not yet exist, treat as non-symlink
+		if os.IsNotExist(err) {
+			return path, false, nil
+		}
+		return "", false, err
+	}
+	if fi.Mode()&os.ModeSymlink == 0 {
+		return path, false, nil
+	}
+	newpath, err = os.Readlink(realPath)
+	if err != nil {
+		return "", false, err
+	}
+	*linksWalked++
+	return newpath, true, nil
+}
+
+func walkLinks(root, path string, linksWalked *int) (string, error) {
+	switch dir, file := filepath.Split(path); {
+	case dir == "":
+		newpath, _, err := walkLink(root, file, linksWalked)
+		return newpath, err
+	case file == "":
+		if os.IsPathSeparator(dir[len(dir)-1]) {
+			if dir == "/" {
+				return dir, nil
+			}
+			return walkLinks(root, dir[:len(dir)-1], linksWalked)
+		}
+		newpath, _, err := walkLink(root, dir, linksWalked)
+		return newpath, err
+	default:
+		newdir, err := walkLinks(root, dir, linksWalked)
+		if err != nil {
+			return "", err
+		}
+		newpath, islink, err := walkLink(root, filepath.Join(newdir, file), linksWalked)
+		if err != nil {
+			return "", err
+		}
+		if !islink {
+			return newpath, nil
+		}
+		if filepath.IsAbs(newpath) {
+			return newpath, nil
+		}
+		return filepath.Join(newdir, newpath), nil
+	}
+}
diff --git a/vendor/github.com/containerd/continuity/fs/stat_bsd.go b/vendor/github.com/containerd/continuity/fs/stat_bsd.go
new file mode 100644
index 000000000..cb7400a33
--- /dev/null
+++ b/vendor/github.com/containerd/continuity/fs/stat_bsd.go
@@ -0,0 +1,44 @@
+// +build darwin freebsd
+
+/*
+   Copyright The containerd Authors.
+
+   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.
+*/
+
+package fs
+
+import (
+	"syscall"
+	"time"
+)
+
+// StatAtime returns the access time from a stat struct
+func StatAtime(st *syscall.Stat_t) syscall.Timespec {
+	return st.Atimespec
+}
+
+// StatCtime returns the created time from a stat struct
+func StatCtime(st *syscall.Stat_t) syscall.Timespec {
+	return st.Ctimespec
+}
+
+// StatMtime returns the modified time from a stat struct
+func StatMtime(st *syscall.Stat_t) syscall.Timespec {
+	return st.Mtimespec
+}
+
+// StatATimeAsTime returns the access time as a time.Time
+func StatATimeAsTime(st *syscall.Stat_t) time.Time {
+	return time.Unix(int64(st.Atimespec.Sec), int64(st.Atimespec.Nsec)) // nolint: unconvert
+}
diff --git a/vendor/github.com/containerd/continuity/fs/stat_linux.go b/vendor/github.com/containerd/continuity/fs/stat_linux.go
new file mode 100644
index 000000000..4a678dd1f
--- /dev/null
+++ b/vendor/github.com/containerd/continuity/fs/stat_linux.go
@@ -0,0 +1,43 @@
+/*
+   Copyright The containerd Authors.
+
+   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.
+*/
+
+package fs
+
+import (
+	"syscall"
+	"time"
+)
+
+// StatAtime returns the Atim
+func StatAtime(st *syscall.Stat_t) syscall.Timespec {
+	return st.Atim
+}
+
+// StatCtime returns the Ctim
+func StatCtime(st *syscall.Stat_t) syscall.Timespec {
+	return st.Ctim
+}
+
+// StatMtime returns the Mtim
+func StatMtime(st *syscall.Stat_t) syscall.Timespec {
+	return st.Mtim
+}
+
+// StatATimeAsTime returns st.Atim as a time.Time
+func StatATimeAsTime(st *syscall.Stat_t) time.Time {
+	// The int64 conversions ensure the line compiles for 32-bit systems as well.
+	return time.Unix(int64(st.Atim.Sec), int64(st.Atim.Nsec)) // nolint: unconvert
+}
diff --git a/vendor/github.com/containerd/continuity/fs/time.go b/vendor/github.com/containerd/continuity/fs/time.go
new file mode 100644
index 000000000..cde456123
--- /dev/null
+++ b/vendor/github.com/containerd/continuity/fs/time.go
@@ -0,0 +1,29 @@
+/*
+   Copyright The containerd Authors.
+
+   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.
+*/
+
+package fs
+
+import "time"
+
+// Gnu tar and the go tar writer don't have sub-second mtime
+// precision, which is problematic when we apply changes via tar
+// files, we handle this by comparing for exact times, *or* same
+// second count and either a or b having exactly 0 nanoseconds
+func sameFsTime(a, b time.Time) bool {
+	return a == b ||
+		(a.Unix() == b.Unix() &&
+			(a.Nanosecond() == 0 || b.Nanosecond() == 0))
+}