Locker.Locked(): clarify that we're checking for write locks

Clarify that Locker.Locked() checks if we have a write lock, since
that's what we care about whenever we check it.

Signed-off-by: Nalin Dahyabhai <nalin@redhat.com>

images.go

@@ -291,7 +291,7 @@ func (r *imageStore) Save() error {
 		return errors.Wrapf(ErrStoreIsReadOnly, "not allowed to modify the image store at %q", r.imagespath())
 	}
 	if !r.Locked() {
-		return errors.New("image store is not locked")
+		return errors.New("image store is not locked for writing")
 	}
 	rpath := r.imagespath()
 	if err := os.MkdirAll(filepath.Dir(rpath), 0700); err != nil {

layers.go

@@ -378,7 +378,7 @@ func (r *layerStore) Save() error {
 		return errors.Wrapf(ErrStoreIsReadOnly, "not allowed to modify the layer store at %q", r.layerspath())
 	}
 	if !r.Locked() {
-		return errors.New("layer store is not locked")
+		return errors.New("layer store is not locked for writing")
 	}
 	rpath := r.layerspath()
 	if err := os.MkdirAll(filepath.Dir(rpath), 0700); err != nil {

lockfile.go

@@ -35,7 +35,7 @@ type Locker interface {
 	// IsReadWrite() checks if the lock file is read-write
 	IsReadWrite() bool
 
-	// Locked() checks if lock is locked
+	// Locked() checks if lock is locked for writing by a thread in this process
 	Locked() bool
 }
 

lockfile_unix.go

@@ -139,9 +139,11 @@ func (l *lockfile) Unlock() {
 	l.stateMutex.Unlock()
 }
 
-// Locked checks if lockfile is locked.
+// Locked checks if lockfile is locked for writing by a thread in this process.
 func (l *lockfile) Locked() bool {
-	return l.locked
+	l.stateMutex.Lock()
+	defer l.stateMutex.Unlock()
+	return l.locked && (l.locktype == unix.F_WRLCK)
 }
 
 // Touch updates the lock file with the UID of the user.