package archive import ( "archive/tar" "os" "path/filepath" "strings" "syscall" "github.com/docker/docker/pkg/system" ) func getWhiteoutConverter(format WhiteoutFormat) tarWhiteoutConverter { if format == OverlayWhiteoutFormat { return overlayWhiteoutConverter{} } return nil } type overlayWhiteoutConverter struct{} func (overlayWhiteoutConverter) ConvertWrite(hdr *tar.Header, path string, fi os.FileInfo) (wo *tar.Header, err error) { // convert whiteouts to AUFS format if fi.Mode()&os.ModeCharDevice != 0 && hdr.Devmajor == 0 && hdr.Devminor == 0 { // we just rename the file and make it normal dir, filename := filepath.Split(hdr.Name) hdr.Name = filepath.Join(dir, WhiteoutPrefix+filename) hdr.Mode = 0600 hdr.Typeflag = tar.TypeReg hdr.Size = 0 } if fi.Mode()&os.ModeDir != 0 { // convert opaque dirs to AUFS format by writing an empty file with the prefix opaque, err := system.Lgetxattr(path, "trusted.overlay.opaque") if err != nil { return nil, err } if len(opaque) == 1 && opaque[0] == 'y' { if hdr.Xattrs != nil { delete(hdr.Xattrs, "trusted.overlay.opaque") } // create a header for the whiteout file // it should inherit some properties from the parent, but be a regular file wo = &tar.Header{ Typeflag: tar.TypeReg, Mode: hdr.Mode & int64(os.ModePerm), Name: filepath.Join(hdr.Name, WhiteoutOpaqueDir), Size: 0, Uid: hdr.Uid, Uname: hdr.Uname, Gid: hdr.Gid, Gname: hdr.Gname, AccessTime: hdr.AccessTime, ChangeTime: hdr.ChangeTime, } } } return } func (overlayWhiteoutConverter) ConvertRead(hdr *tar.Header, path string) (bool, error) { base := filepath.Base(path) dir := filepath.Dir(path) // if a directory is marked as opaque by the AUFS special file, we need to translate that to overlay if base == WhiteoutOpaqueDir { err := syscall.Setxattr(dir, "trusted.overlay.opaque", []byte{'y'}, 0) // don't write the file itself return false, err } // if a file was deleted and we are using overlay, we need to create a character device if strings.HasPrefix(base, WhiteoutPrefix) { originalBase := base[len(WhiteoutPrefix):] originalPath := filepath.Join(dir, originalBase) if err := syscall.Mknod(originalPath, syscall.S_IFCHR, 0); err != nil { return false, err } if err := os.Chown(originalPath, hdr.Uid, hdr.Gid); err != nil { return false, err } // don't write the file itself return false, nil } return true, nil }