discipline for this tty will occur until it
completes successfully. Can sleep.
-write() - A process is writing data from user space
- through the line discipline. Multiple write calls
- are serialized by the tty layer for the ldisc. May
- sleep.
+write() - A process is writing data through the line
+ discipline. Multiple write calls are serialized
+ by the tty layer for the ldisc. May sleep.
flush_buffer() - May be called at any point between open and close.