DEVIOCGET question

[Richard Mark]

I have a question about DEVIOCGET.

First the background: VAX 11/750, Ultrix 2.0-1

What routines or what actions cause an ioctl(DEVIOCGET) call?
What devices need to handle an ioctl(DEVIOCGET) call?

We have a specialized UNIBUS device (HSPI) which we are trying to get
connected and running on our system.  I added the device in the
config file, made the appropriate entries in files.vax, placed the
driver sources in /sys/vaxuba, added the appropriate stuff in the cdevsw 
table of the conf.c file and made the appropriate /dev/hspi0 node with the
correct access rights (crw-rw-rw).  I completed reconfiguring, rebuilding 
and rebooting the new system without problems.  I had problems opening 

I had problems opening the device for reading and writing but no problems
when opening for just reading.  To debug my problem I put printfs 
in the driver code (in the hspiopen() and hspiioclt() routines)

When I open("/dev/hspi0",O_RDONLY) it called hspiopen() which calls
hspiioctl(cmd=START) returns from hspiioctl() successfully, then
returns from hspiopen() successfully and the open() returns successfully.

When I open("/dev/hspi0",O_RDWR) it called hspiopen() which calls
hspiioctl(cmd=START) returns from hspiioctl() successfully, then
returns from hspiopen() successfully THEN it calls hspiioctl(cmd=DEVIOCGET)
and the open() returns unsuccessfully.  Although hspiioctl() does not
handle that case, there is a default case which doesn't do anything
and still returns from hspiioctl() successfully.

To repeat my original questions:
What routines or what actions cause an ioctl(DEVIOCGET) call?
What devices need to handle an ioctl(DEVIOCGET) call?

And now some more questions:
Is this specific to a certain version of Ultrix?
Where can I find out what values I should put in the devget struct?
Where is any of this documented?

I have probably left out some details or not explained somethings
clearly enough but hopefully someone will have some clue about my
problem.  If you need more info, drop me a note.

Thanks,

Rich
rmark at lll-lcc.llnl.gov