Missing SysV tty device driver feature??

[Uwe Doering]

peter at ficc.ferranti.com (Peter da Silva) writes:

>In article <ZOIN42U at geminix.in-berlin.de> gemini at geminix.in-berlin.de (Uwe Doering) writes:
>> In most SysV tty drivers the assertion of DTR doesn't depend on the CLOCAL
>> flag. It is always raised if at least one process has opened the device,
>> and is dropped if the last process closes the device.
>
>It is also dropped if CLOCAL is clear and the speed is set to B0. Which

Just to nitpick again :-) : This is implementation dependent, too.
If you think of DTR as being independent of the CLOCAL flag (as I stated
above), setting the line speed to B0 will drop DTR regardless of the
CLOCAL flag. After all, the only purpose of B0 _is_ to drop DTR. Therefor,
even in theory, there is no need to link its behaviour to the state of
the CLOCAL flag.

I admit that there may be drivers out in the real world that work the
way Peter described, but you can't rely on it. In FAS, for instance,
CLOCAL controls only the carrier detect handling, but not DTR. Yes, I
know that FAS isn't the measure of all things. :-)

I wonder what the author of the termio(7) man page thinks about these
special cases.

>is lucky, because of the difficulty of re-opening ones control terminal
>while process group leader... you don't have a control terminal any more
>and you can't get one because setpgrp fails if you're already process
>group leader. Gritch.

I agree. The assignment of controlling terminals to processes is rather
awkward under SysV. :-(

      Uwe
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