for 1 second's worth of input) and larger tty output buffers. The
interrupt-level buffers are still too small for speeds above 115200
bps (only a little too small for 230400 bps if RTS flow control is
enabled).
Don't call ttsetwater() explicitly in open(). It is now called for
the TTYDISC l_open() and should be static.
Don't attempt to register the cdevsw more than once.
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