Re: [GIT PULL FOR 3.6] V4L2 API cleanups

[Laurent Pinchart <laurent.pinchart@ideasonboard.com>]

Hi Sakari,

On Monday 11 June 2012 12:39:44 Sakari Ailus wrote:
> On Mon, Jun 11, 2012 at 09:50:54AM +0200, Laurent Pinchart wrote:
> > On Sunday 10 June 2012 23:22:59 Sakari Ailus wrote:
> > > Hi Mauro,
> > > 
> > > Here are two V4L2 API cleanup patches; the first removes __user from
> > > videodev2.h from a few places, making it possible to use the header file
> > > as such in user space, while the second one changes the
> > > v4l2_buffer.input field back to reserved.
> > > 
> > > The following changes since commit 
5472d3f17845c4398c6a510b46855820920c2181:
> > >   [media] mt9m032: Implement V4L2_CID_PIXEL_RATE control (2012-05-24
> > > 
> > > 09:27:24 -0300)
> > > 
> > > are available in the git repository at:
> > >   ssh://linuxtv.org/git/sailus/media_tree.git media-for-3.6
> > > 
> > > Sakari Ailus (2):
> > >       v4l: Remove __user from interface structure definitions
> > 
> > NAK, sorry.
> > 
> > __user has a purpose, we need to add it where it's missing, not remove it
> > where it's rightfully present.
> 
> It's not quite as simple as adding __user everywhere it might belong to ---
> these structs are being used in kernel space, too. The structs that are part
> of the user space interface may at some point contain pointers to memory
> which is in user space. That is being dealt by video_usercopy(), so the
> individual drivers or the rest of the V4L2 framework always gets pointers
> pointing to kernel memory.

Very good point, I haven't thought about that. I'm not sure how to deal with 
this, splitting structures in a __user and a non __user version isn't really a 
good option. Maybe the sparse tool should be somehow extended ?

> These particular fields aren't handled by the framework currently, so
> removing __user there requires adding the support to video_usercopy().

-- 
Regards,

Laurent Pinchart