According to Paul A Vixie <paul@vix.com> :
> 
> I've always preferred to have O_NONBLOCK just be a way to force an
> EWOULDBLOCK errno rather than a way to bypass carrier checking, but
> I don't know how to get a tty device open (so I can set its CLOCAL)
> if its carrier isn't up unless we use O_NONBLOCK on tty devices to
> mean "ignore carrier when opening, but return EIO on read and write
> unless either carrier is on or CLOCAL is on".  Maybe a new open flag
> like O_IGNCARR?

In a more tolerant light, you may want to perceive O_NONBLOCK as being 
overloaded in the instance of opening a tty.  In which case, a 
different name for the same flag would be sufficient clarification.

Not perfectly elegant, but nor is adding a lot of distinct conditions 
to an already bloated IOCTL space.
-- 
Lucio de Re (lucio@proxima.alt.za)
Disclaimer: I'm working at getting my opinions to agree with me.