linux-kernel - Re: Which one corresponds to ioctl in the file

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Message-Id: <201112011022.12686.tvrtko.ursulin@onelan.co.uk>
Date:	Thu, 1 Dec 2011 10:22:12 +0000
From:	Tvrtko Ursulin <tvrtko.ursulin@...lan.co.uk>
To:	Peng Yu <pengyu.ut@...il.com>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: Which one corresponds to ioctl in the file_operations struct in linux/fs.h?

On Thursday 01 Dec 2011 07:40:49 Peng Yu wrote:
> Hi,
> 
> I have some driver code for older version of kernel. It refers to
> ioctl in the file_operations struct. But this field is change in
> kernel 3.0.0-13
> 
> I find the following in linux/fs.h
> 
> 1566   long (*unlocked_ioctl) (struct file *, unsigned int, unsigned long);
> 1567   long (*compat_ioctl) (struct file *, unsigned int, unsigned long);
> 
> Does anybody know which one I should use in order to migrate the
> driver code to the newer version of kernel? Thanks!

>From Documentation/filesystems/vfs.txt:

  unlocked_ioctl: called by the ioctl(2) system call.

  compat_ioctl: called by the ioctl(2) system call when 32 bit system calls
         are used on 64 bit kernels.

You don't need compat_ioctl if your ioctl arguments are 32/64-bit safe.

For both your code needs to be re-entrant or take appropriate locks 
internally.

Hope this helps,

Tvrtko
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