struct file            struct file_operations
+-------------+        +------------------------+
|    . . .    |   +--> |         . . .          |   +--> xyz_write()
+-------------+   |    +------------------------+   |
|    f_op     | --+    |         write          | --+
+-------------+        +------------------------+
|    . . .    |        |         . . .          |
+-------------+        +------------------------+