What defines an "exceptional condition" in 4.[23]BSD

[Roy Smith]

	I've run across what seems to be an inconsistancy in the way
exceptional conditions are handled in 4.[23]BSD.  When OOB data is pending
on a socket, a select(2) for exceptions on the socket descriptor will
return; in addition, a SIGURG is sent.  If you have a pty in TIOCPKT or
TIOCUCNTL mode and a control packet or ioctl command comes in, you also
break out of a select(2), but no SIGURG is sent.

	Is there some reason why one sends a SIGURG but not the other?  Are
there any other conditions in the system other than OOB data and the
TIOCPKT/TIOCUCNTL cases described above which generate exceptional
conditions?  Do they send SIGURGs and/or break out of selects?  Should they?
-- 
Roy Smith, System Administrator
Public Health Research Institute
455 First Avenue, New York, NY 10016
{allegra,philabs,cmcl2,rutgers}!phri!roy -or- phri!roy at uunet.uu.net