afs: Flush outstanding writes when an fd is closed

Flush outstanding writes in afs when an fd is closed.  This is what NFS and
CIFS do.

Reported-by: Marc Dionne <marc.c.dionne@gmail.com>
Signed-off-by: David Howells <dhowells@redhat.com>
diff --git a/fs/afs/write.c b/fs/afs/write.c
index ea66890..f1450ea 100644
--- a/fs/afs/write.c
+++ b/fs/afs/write.c
@@ -758,6 +758,20 @@
 }
 
 /*
+ * Flush out all outstanding writes on a file opened for writing when it is
+ * closed.
+ */
+int afs_flush(struct file *file, fl_owner_t id)
+{
+	_enter("");
+
+	if ((file->f_mode & FMODE_WRITE) == 0)
+		return 0;
+
+	return vfs_fsync(file, 0);
+}
+
+/*
  * notification that a previously read-only page is about to become writable
  * - if it returns an error, the caller will deliver a bus error signal
  */