Re: procedure for creating new ioctl?

[Richard B. Johnson]

On Mon, 10 Jun 2002, Joseph Cheek wrote:

> hi all,
> 
> i'd like to create a new ioctl for use in my kernels [actually i already 
> have 8-)] but want to make sure that i follow any established procedure 
> for creating it before requesting it be included in the kernel. 
>  specifically, is there a way to ensure the ioctl number i use isn't in 
> use by anyone else?  is there a central registry?
> 
> so far i've just picked an arbitrary number:
> 
> sanfrancisco:/usr/src/linux-2.4.17/include/linux# diff -Naur kd.h{.orig,}
> --- kd.h.orig   Mon Jun 10 11:08:22 2002
> +++ kd.h        Thu Jun  6 16:00:33 2002
> @@ -177,4 +177,6 @@
>     don't reuse for the time being */
>  /* note: 0x4B60-0x4B6D, 0x4B70-0x4B72 used above */
> 
> +#define KDGETKEYDOWNSTATE      0x4B80  /* read kernel keydown bit */
> +
>  #endif /* _LINUX_KD_H */
> 
> any tips, pointers appreciated.
> 
> joe
> 

I use SIOCDEVPRIVATE as the starting value for new ioctls:

/*
 *   Interface to the private device functions. User API sees this only.
 */
#define CHEK_SEEPROM   SIOCDEVPRIVATE + 0x07
#define READ_SEEPROM   SIOCDEVPRIVATE + 0x08
#define WRITE_SEEPROM  SIOCDEVPRIVATE + 0x09

I've seen this in several drivers. I think this is the way to do it
so there is no interference with other ioctls.

Cheers,
Dick Johnson

Penguin : Linux version 2.4.18 on an i686 machine (797.90 BogoMips).

                 Windows-2000/Professional isn't.