1 files changed, 37 insertions, 0 deletions
diff --git a/tests/cluster/cluster_test.go b/tests/cluster/cluster_test.go
index 2e969ce..def03f1 100644
--- a/tests/cluster/cluster_test.go
+++ b/tests/cluster/cluster_test.go
@@ -10,8 +10,11 @@ import (
 	"math/rand"
 	"os"
 	"sync"
+	"syscall"
 	"testing"
 
+	"golang.org/x/sys/unix"
+
 	"github.com/rfjakob/gocryptfs/v2/tests/test_helpers"
 )
 
@@ -109,3 +112,37 @@ func TestClusterConcurrentRW(t *testing.T) {
 	go readThread(f2)
 	wg.Wait()
 }
+
+// Check that byte-range locks work on an empty file
+func TestFcntlFlock(t *testing.T) {
+	path := test_helpers.TmpDir + "/" + t.Name()
+
+	fd1, err := syscall.Open(path, syscall.O_CREAT|syscall.O_WRONLY|syscall.O_EXCL, 0600)
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer syscall.Close(fd1)
+
+	// F_OFD_SETLK locks on the same fd always succeed, so we have to
+	// open a 2nd time.
+	fd2, err := syscall.Open(path, syscall.O_RDWR, 0)
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer syscall.Close(fd2)
+
+	lk := unix.Flock_t{
+		Type:   unix.F_WRLCK,
+		Whence: unix.SEEK_SET,
+		Start:  0,
+		Len:    0,
+	}
+	err = unix.FcntlFlock(uintptr(fd1), unix.F_OFD_SETLK, &lk)
+	if err != nil {
+		t.Fatal(err)
+	}
+	err = unix.FcntlFlock(uintptr(fd2), unix.F_OFD_SETLK, &lk)
+	if err == nil {
+		t.Fatal("double-lock succeeded but should have failed")
+	}
+}