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From: Kristis Makris <kristis.makris@asu.edu>
To: Matthew Jacob <lydianconcepts@gmail.com>
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Date: Tue, 05 Sep 2006 19:09:11 -0700
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Cc: freebsd-drivers@freebsd.org
Subject: Re: ioctl: uiomove, copyin, copyout
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> Check the format of your ioctl code to make sure that it follows BSD
> rules for getting passed to your driver w/o interpretation. Linux IIRC
> follows SYSV ioctl semantics, which means that the ioctl is never
> interpreted by the kernel above the driver. BSD ioctls semantics looks
> at the type nibble to decide whether the ioctl parameters can be
> copied directly to the kernel and presented to driver as a pointer you
> can just de-reference rather than a pointer you have to perform copyin
> on.
> 
> Check sys/ioccom.h.

That was it. I learned something new today. Thanks a lot.