Linux compat ioctl return values

[Pieter de Boer]

Hi,

I've been working on a kernel driver that creates a device. This device
in turn is opened and ioctl'd from a Linux executable. I've registered a
handler for these ioctl's and my ioctl handler is succesfully executed.

My ioctl-handler returns a large positive value, but the userland
application retrieves the value 1, EPERM. If I return 42, the userland
application retrieves 42, but 260 is retrieved as 1. It appears there's a
threshold somewhere above which the return value is set to 1, but I
haven't been able to find out where in the code this is done. The Linux
executable actually expects the value I return, and doesn't work when
EPERM is found instead.

So, the question is: does anyone know where such a threshold may
reside and how to work around it?

Thanks,
Pieter