archive: Handle aufs plink hardlinks in ApplyLayer

Files in the .wh..wh.plnk directory are ignored, but other files
inside the tarfile can be hardlinks to these files. This is not
something that normally happens, as on aufs unmount such files are
supposed to be dropped via the "auplink" too, yet images on the index
(such as shipyard/shipyard, e.g. layer
f73c835af6d58b6fc827b400569f79a8f28e54f5bb732be063e1aacefbc374d0)
contains such files.

We handle these by extracting these files to a temporary directory
and resolve such hardlinks via the temporary files.

This fixes https://github.com/dotcloud/docker/issues/3884

Docker-DCO-1.1-Signed-off-by: Alexander Larsson <alexl@redhat.com> (github: alexlarsson)

archive/archive.go

@@ -186,7 +186,7 @@ func addTarFile(path, name string, tw *tar.Writer) error {
 	return nil
 }
 
-func createTarFile(path, extractDir string, hdr *tar.Header, reader *tar.Reader) error {
+func createTarFile(path, extractDir string, hdr *tar.Header, reader io.Reader) error {
 	switch hdr.Typeflag {
 	case tar.TypeDir:
 		// Create directory unless it exists as a directory already.

archive/diff.go

@@ -2,7 +2,9 @@ package archive
 
 import (
 	"code.google.com/p/go/src/pkg/archive/tar"
+	"fmt"
 	"io"
+	"io/ioutil"
 	"os"
 	"path/filepath"
 	"strings"
@@ -42,6 +44,9 @@ func ApplyLayer(dest string, layer ArchiveReader) error {
 
 	var dirs []*tar.Header
 
+	aufsTempdir := ""
+	aufsHardlinks := make(map[string]*tar.Header)
+
 	// Iterate through the files in the archive.
 	for {
 		hdr, err := tr.Next()
@@ -72,6 +77,22 @@ func ApplyLayer(dest string, layer ArchiveReader) error {
 
 		// Skip AUFS metadata dirs
 		if strings.HasPrefix(hdr.Name, ".wh..wh.") {
+			// Regular files inside /.wh..wh.plnk can be used as hardlink targets
+			// We don't want this directory, but we need the files in them so that
+			// such hardlinks can be resolved.
+			if strings.HasPrefix(hdr.Name, ".wh..wh.plnk") && hdr.Typeflag == tar.TypeReg {
+				basename := filepath.Base(hdr.Name)
+				aufsHardlinks[basename] = hdr
+				if aufsTempdir == "" {
+					if aufsTempdir, err = ioutil.TempDir("", "dockerplnk"); err != nil {
+						return err
+					}
+					defer os.RemoveAll(aufsTempdir)
+				}
+				if err := createTarFile(filepath.Join(aufsTempdir, basename), dest, hdr, tr); err != nil {
+					return err
+				}
+			}
 			continue
 		}
 
@@ -96,7 +117,26 @@ func ApplyLayer(dest string, layer ArchiveReader) error {
 				}
 			}
 
-			if err := createTarFile(path, dest, hdr, tr); err != nil {
+			srcData := io.Reader(tr)
+			srcHdr := hdr
+
+			// Hard links into /.wh..wh.plnk don't work, as we don't extract that directory, so
+			// we manually retarget these into the temporary files we extracted them into
+			if hdr.Typeflag == tar.TypeLink && strings.HasPrefix(filepath.Clean(hdr.Linkname), ".wh..wh.plnk") {
+				linkBasename := filepath.Base(hdr.Linkname)
+				srcHdr = aufsHardlinks[linkBasename]
+				if srcHdr == nil {
+					return fmt.Errorf("Invalid aufs hardlink")
+				}
+				tmpFile, err := os.Open(filepath.Join(aufsTempdir, linkBasename))
+				if err != nil {
+					return err
+				}
+				defer tmpFile.Close()
+				srcData = tmpFile
+			}
+
+			if err := createTarFile(path, dest, srcHdr, srcData); err != nil {
 				return err
 			}