what does EIO from open("/dev/tty", 0) == -1 mean ?

[Ronald Khoo]

[warning: info-unix people note:  this may well be a XENIX question... :-)]

Hi - something's puzzling me:

When our members try and use rn over the modem lines, occasionally they
get Can't open /dev/tty, which persists for the whole of their session.
I made it print errno, which was 5 (EIO).  My man page for open(2)
(which is called open(S) in xenixish .. grrr..) says not a peep about
EIO. 

What's wrong? What does it mean?

[I haven't confused it with ENXIO, just in case someone thinks I've lost
 the control tty, I've thought of that.]

I've got a workraround - Larry just uses it to open(, O_NDELAY) instead
of FIONREAD, so I substituted rdchk() instead, and that seems to work,
but I'd STILL like to know what it means...

Anyone?

[interesting email replies will be summarised, others > /dev/null on
 YOUR side of the atlantic, please, European email costs $$ !]

CONFIG=SCO386 2.2.3, Compaq 386 - if that's relevant.... Oh, and builtin
drivers on Arnet and AST dumb serial 4-ports.

Thanks in advance

-- 
Ronald Khoo @ The IBM PC User Group, PO Box 360, Harrow HA1 4LQ
Phone:	+44 -1- 863 1191			Domain:	ronald at ibmpcug.CO.UK
Path:	...!ukc!slxsys!ibmpcug!ronald    	Fax:    +44 -1- 863 6095