diff --git a/samples/flushfs/flush_fs_test.go b/samples/flushfs/flush_fs_test.go
index f804284..4885357 100644
--- a/samples/flushfs/flush_fs_test.go
+++ b/samples/flushfs/flush_fs_test.go
@@ -66,12 +66,6 @@ func (t *flushFSTest) setUp(
 	// Set up test config.
 	t.MountType = "flushfs"
 	t.MountFlags = []string{
-		"--flushfs.flushes_file",
-		t.flushes.Name(),
-
-		"--flushfs.fsyncs_file",
-		t.fsyncs.Name(),
-
 		"--flushfs.flush_error",
 		fmt.Sprintf("%d", int(flushErr)),
 
@@ -79,6 +73,11 @@ func (t *flushFSTest) setUp(
 		fmt.Sprintf("%d", int(fsyncErr)),
 	}
 
+	t.MountFiles = map[string]*os.File{
+		"flushfs.flushes_file": t.flushes,
+		"flushfs.fsyncs_file":  t.fsyncs,
+	}
+
 	t.SubprocessTest.SetUp(ti)
 }
 
diff --git a/samples/mount_sample/mount.go b/samples/mount_sample/mount.go
index 963186c..48f860d 100644
--- a/samples/mount_sample/mount.go
+++ b/samples/mount_sample/mount.go
@@ -31,30 +31,21 @@ import (
 var fType = flag.String("type", "", "The name of the samples/ sub-dir.")
 var fMountPoint = flag.String("mount_point", "", "Path to mount point.")
 
-var fFlushesFile = flag.String("flushfs.flushes_file", "", "")
-var fFsyncsFile = flag.String("flushfs.fsyncs_file", "", "")
+var fFlushesFile = flag.Uint64("flushfs.flushes_file", 0, "")
+var fFsyncsFile = flag.Uint64("flushfs.fsyncs_file", 0, "")
 var fFlushError = flag.Int("flushfs.flush_error", 0, "")
 var fFsyncError = flag.Int("flushfs.fsync_error", 0, "")
 
 func makeFlushFS() (fs fuse.FileSystem, err error) {
 	// Check the flags.
-	if *fFlushesFile == "" || *fFsyncsFile == "" {
+	if *fFlushesFile == 0 || *fFsyncsFile == 0 {
 		err = fmt.Errorf("You must set the flushfs flags.")
 		return
 	}
 
-	// Open the files.
-	flushes, err := os.OpenFile(*fFlushesFile, os.O_RDWR, 0)
-	if err != nil {
-		err = fmt.Errorf("Opening %s: %v", *fFlushesFile, err)
-		return
-	}
-
-	fsyncs, err := os.OpenFile(*fFsyncsFile, os.O_RDWR, 0)
-	if err != nil {
-		err = fmt.Errorf("Opening %s: %v", *fFsyncsFile, err)
-		return
-	}
+	// Set up the files.
+	flushes := os.NewFile(uintptr(*fFlushesFile), "(flushes file)")
+	fsyncs := os.NewFile(uintptr(*fFsyncsFile), "(fsyncs file)")
 
 	// Set up errors.
 	var flushErr error
diff --git a/samples/subprocess.go b/samples/subprocess.go
index 6161ed6..5db0ca6 100644
--- a/samples/subprocess.go
+++ b/samples/subprocess.go
@@ -20,6 +20,7 @@ import (
 	"io"
 	"io/ioutil"
 	"log"
+	"os"
 	"os/exec"
 	"path"
 	"sync"
@@ -40,6 +41,10 @@ type SubprocessTest struct {
 	// Additional flags to be passed to the mount_sample tool.
 	MountFlags []string
 
+	// A list of files to pass to mount_sample. The given string flag will be
+	// used to pass the file descriptor number.
+	MountFiles map[string]*os.File
+
 	// A context object that can be used for long-running operations.
 	Ctx context.Context
 
@@ -132,7 +137,7 @@ func (t *SubprocessTest) initialize() (err error) {
 		return
 	}
 
-	// Set up a command.
+	// Set up basic args for the subprocess.
 	args := []string{
 		"--type",
 		t.MountType,
@@ -142,9 +147,22 @@ func (t *SubprocessTest) initialize() (err error) {
 
 	args = append(args, t.MountFlags...)
 
+	// Set up inherited files and appropriate flags.
+	var extraFiles []*os.File
+	for flag, file := range t.MountFiles {
+		// Cf. os/exec.Cmd.ExtraFiles
+		fd := 3 + len(extraFiles)
+
+		extraFiles = append(extraFiles, file)
+		args = append(args, "--"+flag)
+		args = append(args, fmt.Sprintf("%d", fd))
+	}
+
+	// Set up a command.
 	t.mountCmd = exec.Command(toolPath, args...)
 	t.mountCmd.Stdout = &t.mountStdout
 	t.mountCmd.Stderr = &t.mountStderr
+	t.mountCmd.ExtraFiles = extraFiles
 
 	// Start it.
 	if err = t.mountCmd.Start(); err != nil {