This is probably incomplete. Is locking needed? Should we notify the
next writer (if any) that the port is writable when flushing the output?
Change-Id: I2566e2d036a61af4819894a44f57603179aa27df
Reviewed-on: https://review.haiku-os.org/c/haiku/+/2516
Reviewed-by: Adrien Destugues <[email protected]>