Help: close() returns -1

[Jack Morrison]

Oh mighty wizards of device drivers:

I have written a simple driver for a parallel port on a Sun 3/260.
Everything works except for one thing: close() returns an error
status (-1), with errno=1 (not owner).

The device entry is

c-w--w--w-  1 root      63,   0 Feb  2 15:07 /dev/vs0

My test program calls open("/dev/vs0", 1), which returns a valid fd.
If I then call close(fd), all is fine. 

If I write(fd, buf, n) first, the time on the /dev entry changes, 
and the data actually goes out properly; then when I call close,
the /dev entry goes back to its previous time and close(fd) returns -1. 

If I do this as root, or if I chown the /dev entry to my username, 
close() returns 0.

If I go through the same motions with /dev/null, close() returns 0
and the time on the /dev/null entry remains updated after the close
(the owner stays root).

Changing permissions on /dev/vs0 doesn't help. 

My driver always returns 0 from a vsclose() call.

If more than one process opens /dev/vs0, only the last process to 
close it gets the error (the kernel shouldn't call the driver
close() routine until the last process closes the device).

Any ideas? Many thanks.
-- 
Jack C. Morrison, Jet Propulsion Laboratory
"How am I typing? Call 1-818-354-3722, or mail jack at robotics.jpl.nasa.gov"