Bidirectional uucp on STREAMS-based TTY?

Steve Wingard wingard at ncrcae.Columbia.NCR.COM
Fri Mar 2 08:28:48 AEST 1990


It didn't appear that my last posting made it out of here, so
I'm going to try again.  Excuse me if you've seen this before...

I'm having trouble establishing a bidirectional uucp line on a
STREAMS-based TTY device.  The typical way to do this (running
uugetty on the device from inittab) causes problems with outgoing
cu calls because of the behavior of stropen().

Since uugetty's open of the TTY device waits for the DCD signal to
be asserted, the stropen() call sits within its section where
the STRWOPEN flag is set.  Any subsequent open of the device 
(by cu, for instance) will sleep regardless of the setting of
the O_NDELAY flag because uugetty's stropen() call will not 
complete, clearing the STRWOPEN flag, until an incoming call is
received.

The problem could be avoided by changing uugetty to open the device
with O_NDELAY set also -- but this could cause problems with garbage
characters coming in from the modem and wreaking havoc with uugetty.
stropen() could also be modified to let processes continue past the
STRWOPEN test if the O_NDELAY flag is set, but that could have dangerous
implications as well (opening a stream that is in the process of being
created or dismantled by another process).  Has anyone developed any other
workaround to the situation?  Suggestions would be welcome...



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