Re: compat_ioctl question

From: Arnd Bergmann
Date: Thu Apr 26 2007 - 17:38:25 EST

On Thursday 26 April 2007, Paul Fulghum wrote:
> I need to add ioctl translations for my driver to
> allow 32 bit access on 64 bit systems.
> After digging through the kernel code there seems to be
> 3 methods of doing this:
> 1. define compat_ioctl() file operation for device and
> implement translation code in individual driver
> 2. add COMPATIBLE_IOCTL entry to include/linux/compat_ioctl.h
> to mark an ioctl code as the same in any environment
> 3. add HANDLE_IOCTL entry to fs/compat_ioctl.c with translation code
> implemented in the same file
> There is no way to implement #1 for a tty driver without
> modifying the kernel tty code to allow registration of a
> compat_ioctl() handler.
> #3 would put a lot of driver specific stuff in a common
> kernel file. This method also seems to break if there
> is an ioctl code collision.
> All of these methods involve changes to code outside of my driver.
> --
> Before I spend a lot of time on this I need to know what the
> officially sanctioned method is. I haven't found any definitive
> documentation and a review of mailing list archives does not
> suggest a prevailing opinion.
> Does anyone have pointers on which way would be most likely
> to be accepted as a patch?

It depends a lot on what your specific driver does in the ioctl
handler, but normally you should define a compat_ioctl() function.
What driver are you talking about?

Arnd <><
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