Hi,

I am trying to use the FpIOCtl in the BASEUNIX unit. Guess what? the only thing I get back is -1 !

Is there any example code available on how to talk to a kernel module?

The only kernel that I know to talk to is the one that I am trying is the one that I am writing myself. I am not too familiar with writing device drivers in C. Therefore I would apreciate if someone could sent me an example of a SIMPLE "char" module.

So far, I could register the device using

"register_chrdev(major, name, &fops)"

This seems to work, since I then see the driver in: /proc/modules /proc/devices and /sys/modules

My next step is to issue an FPIOCTL commant but the return code is -1 and the driver never sees the command.

Question:

Do I need open a "file deccriptor" in order to communicate using IOCTL? It should not be?

I have spent the week-end on this, and failed again ... My self esteem is close to nul at this point. Help please...

Thank you

Alain Michaud

Alain Michaud wrote

Do I need open a "file deccriptor" in order to communicate using IOCTL?

Yes, you have to open the device before talking to it. Or what the hell do you think, the "Handle" parameter of

|Function  FpIOCtl      (Handle:cint;Ndx: culong;Data: Pointer):cint;

is for?

As always: RTFM, reading the man page (man 2 ioctl) actually might help too:

|DESCRIPTION
| [...] The argu­ment d must be an open file descriptor. |
|RETURN VALUE
| Usually, on success zero is returned. A few ioctls use | the return value as an output parameter and return a non­ | negative value on success. On error, -1 is returned, and | errno is set appropriately.

BTW, I agree - writing device drivers sucks. I know. :-)

But checking out

http://www.freesoftwaremagazine.com/articles/drivers_linux

may be worth a try.

Regards,

Vinzent.