Dennis Ferguson <dennis.c.ferguson%gmail.com@localhost> writes: > No, /dev/ttydX apparently just meant "attached to a modem" (we didn't do > this). Through 4.3 BSD at least the BSD terminal driver did not have a > separate device for dial out. If you wanted to use a modem for dial out > you would open the same device file as was used for dial in, but with a > O_NONBLOCK flag given to open() followed by some other magic (my memory is > dim) that was supposed to lock out pending opens waiting for carrier. This > was very buggy and full of race conditions, so we avoided trying to share > modems for both dial-in and dial-out use. The /dev/dtyXX thing may have > come from System V (or the System V-based SunOS) and was supposed to fix > the races. Thanks for the explanation of /dev/ttydX. I remember using the dtyXX/ttyXX dual minor devices, for dialout/dialin, and it did work reliably. That might have been on 2.11BSD, or it may have been more recent.
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