Use continuity fs package

Signed-off-by: Brian Goff <cpuguy83@gmail.com>

vendor/github.com/containerd/continuity/fs/diff_unix.go

@@ -0,0 +1,58 @@
+// +build !windows
+
+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
+}