Add fuse.Options.EnableLocks option.

This ensure VFS locking continues working, ensuring backward compatibility.

fuse/api.go

@@ -64,6 +64,7 @@ type MountOptions struct {
 	// Values shown in "df -T" and friends
 	// First column, "Filesystem"
 	FsName string
+
 	// Second column, "Type", will be shown as "fuse." + Name
 	Name string
 
@@ -76,6 +77,10 @@ type MountOptions struct {
 
 	// If set, print debugging information.
 	Debug bool
+
+	// If set, ask kernel to forward file locks to FUSE. If using,
+	// you must implement the GetLk/SetLk/SetLkw methods.
+	EnableLocks bool
 }
 
 // RawFileSystem is an interface close to the FUSE wire protocol.

fuse/nodefs/fuse.go

@@ -8,7 +8,8 @@ import (
 	"github.com/hanwen/go-fuse/fuse"
 )
 
-// Mounts a filesystem with the given root node on the given directory
+// Mounts a filesystem with the given root node on the given directory.
+// Convenience wrapper around fuse.NewServer
 func MountRoot(mountpoint string, root Node, opts *Options) (*fuse.Server, *FileSystemConnector, error) {
 	conn := NewFileSystemConnector(root, opts)
 

fuse/opcode.go

@@ -83,7 +83,11 @@ func doInit(server *Server, req *request) {
 	server.reqMu.Lock()
 	server.kernelSettings = *input
 	server.kernelSettings.Flags = input.Flags & (CAP_ASYNC_READ | CAP_BIG_WRITES | CAP_FILE_OPS |
-		CAP_AUTO_INVAL_DATA | CAP_READDIRPLUS | CAP_NO_OPEN_SUPPORT | CAP_FLOCK_LOCKS | CAP_POSIX_LOCKS)
+		CAP_AUTO_INVAL_DATA | CAP_READDIRPLUS | CAP_NO_OPEN_SUPPORT)
+
+	if server.opts.EnableLocks {
+		server.kernelSettings.Flags |= CAP_FLOCK_LOCKS | CAP_POSIX_LOCKS
+	}
 
 	if input.Minor >= 13 {
 		server.setSplice()

fuse/test/file_lock_test.go

@@ -7,6 +7,7 @@
 package test
 
 import (
+	"io/ioutil"
 	"os"
 	"os/exec"
 	"path/filepath"
@@ -130,10 +131,15 @@ func TestFlockInvoked(t *testing.T) {
 	}
 
 	root := nodefs.NewDefaultNode()
-	s, _, err := nodefs.MountRoot(dir, root, opts)
+	conn := nodefs.NewFileSystemConnector(root, opts)
+	mountOpts := fuse.MountOptions{
+		EnableLocks: true
+	}
+	s, err := fuse.NewServer(conn.RawFS(), dir, &mountOpts)
 	if err != nil {
-		t.Fatalf("MountRoot: %v", err)
+		t.Fatal("NewServer", err)
 	}
+
 	go s.Serve()
 	if err := s.WaitMount(); err != nil {
 		t.Fatal("WaitMount", err)
@@ -150,6 +156,7 @@ func TestFlockInvoked(t *testing.T) {
 	if node.SetLkInvoked() {
 		t.Fatalf("SetLk is invoked")
 	}
+
 	cmd := exec.Command(flock, "--nonblock", realPath, "echo", "locked")
 	out, err := cmd.CombinedOutput()
 	if err != nil {
@@ -171,3 +178,58 @@ func TestFlockInvoked(t *testing.T) {
 		t.Fatalf("SetLkw is not invoked")
 	}
 }
+
+// Test that file system that don't implement locking are still
+// handled in the VFS layer.
+func TestNoLockSupport(t *testing.T) {
+	flock, err := exec.LookPath("flock")
+	if err != nil {
+		t.Skip("flock command not found.")
+	}
+
+	tmp, err := ioutil.TempDir("", "TestNoLockSupport")
+	if err != nil {
+		t.Fatal(err)
+	}
+	mnt, err := ioutil.TempDir("", "TestNoLockSupport")
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	defer os.RemoveAll(tmp)
+	defer os.RemoveAll(mnt)
+
+	opts := &nodefs.Options{
+		Owner: fuse.CurrentOwner(),
+		Debug: testutil.VerboseTest(),
+	}
+	root := nodefs.NewMemNodeFSRoot(tmp)
+
+	lock := fuse.FileLock{}
+	outLock := fuse.FileLock{}
+	ctx := fuse.Context{}
+	if status := root.GetLk(nil, uint64(1), &lock, uint32(0x0), &outLock, &ctx); status != fuse.ENOSYS {
+		t.Fatalf("MemNodeFs should not implement locking")
+	}
+
+	s, _, err := nodefs.MountRoot(mnt, root, opts)
+	if err != nil {
+		t.Fatalf("MountRoot: %v", err)
+	}
+	go s.Serve()
+	if err := s.WaitMount(); err != nil {
+		t.Fatalf("WaitMount: %v", err)
+	}
+	defer s.Unmount()
+
+	fn := mnt + "/file.txt"
+	if err := ioutil.WriteFile(fn, []byte("content"), 0644); err != nil {
+		t.Fatalf("WriteFile: %v", err)
+	}
+
+	cmd := exec.Command(flock, "--nonblock", fn, "echo", "locked")
+	out, err := cmd.CombinedOutput()
+	if err != nil {
+		t.Fatalf("flock %v: %v", err, string(out))
+	}
+}