Subject: Re: Upgrade of `struct vnd_ioctl'
To: Arnaud Lacombe <>
From: Martin Husemann <>
List: tech-kern
Date: 02/11/2007 20:33:16
On Sun, Feb 11, 2007 at 02:27:22PM -0500, Arnaud Lacombe wrote:
> Does the change needs any compatibility layer to be added ? 

Yes - the size of ioctl arguments is encoded in the ioctl cmd code, so you
need to rename the old struct and allocate new numbers for all vnd ioctls
(with the same symbolic name as before), then provide the old (now renamed)
ioctls under the appropriate COMPAT define.

In special cases we decided to break ioctl ABI compatibility - this may be
a case where we could afford it (but I'm mostly indifferent).