linux-kernel - Re: Size of sector_t in userspace [Was: fix 41 'make headers

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Date:	Wed, 21 Jan 2009 12:34:43 +0100
From:	Sam Ravnborg <sam@...nborg.org>
To:	Jens Axboe <jens.axboe@...cle.com>
Cc:	Jaswinder Singh Rajput <jaswinder@...nel.org>,
	Ingo Molnar <mingo@...e.hu>,
	Andrew Morton <akpm@...ux-foundation.org>,
	x86 maintainers <x86@...nel.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: Size of sector_t in userspace [Was: fix 41 'make headers_check' warnings]

On Wed, Jan 21, 2009 at 09:21:25AM +0100, Jens Axboe wrote:
> On Wed, Jan 21 2009, Sam Ravnborg wrote:
> > Hi Jens.
> > 
> > In an attempt to fix some of the issues in our exported Headers jsr
> > encountered some strange stuff in types.h.
> > 
> > types.h is exported to userspace where we do not have access to CONFIG_*
> > symbols.
> > Despite this we use CONFGI_LBD to decide the size of sector_t like this:
> > 
> > #ifdef CONFIG_LBD
> > typedef u64 sector_t;
> > typedef u64 blkcnt_t;
> > #else
> > typedef unsigned long sector_t;
> > typedef unsigned long blkcnt_t;
> > #endif
> > 
> > But as CONFIG_LBD is never defined in userspace sector_t is now 32
> > bit on 32 bit boxes and 64 bit on 64 bit boxes (in userspace).
> > 
> > Is sector:t (and the companion blkcnt_t) really used by userspace?
> > If it is - what size is it expected to have?
> 
> I don't think it's used by userspace, at least it cannot be used in
> userspace <-> kernelspace interactions, since the size isn't fixed.

Thanks Jens.

In that case I suggest we should make it private to the kernel.
We should not expose types from the kernel that is not used
in the kerenl.

Jaswinder - move it inside a ifdef __KERNEL__ / endif block.
Reference Jens' answer above and Cc: Jens on the patch.

Thanks,
	Sam
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