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Date: Fri, 15 Oct 2010 02:03:10 -0700
From: Andrew Morton <akpm@linux-foundation.org>
To: Andi Kleen <andi@firstfloor.org>
Cc: Eric Paris <eparis@redhat.com>, linux-kernel@vger.kernel.org,
        jengelh@medozas.de, davem@davemloft.net
Subject: Re: [PATCH] types.h: define __aligned_u64 and expose to userspace
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On Fri, 15 Oct 2010 10:43:11 +0200 Andi Kleen <andi@firstfloor.org> wrote:

> On Fri, Oct 15, 2010 at 12:24:55AM -0400, Eric Paris wrote:
> > We currently have a kernel internal type called aligned_u64 which aligns
> > __u64's on 8 bytes boundaries even on systems which would normally align
> > them on 4 byte boundaries.  This patch creates a new type __aligned_u64
> > which does the same thing but which is exposed to userspace rather than
> > being kernel internal.
> > 
> > Based-on-patch-by: Andreas Gruenbacher <agruen@suse.de>
> > Signed-off-by: Eric Paris <eparis@redhat.com>
> 
> Acked-by: Andi Kleen <ak@linux.intel.com>
> 
> but only if you:
> 
> > +/* this is a special 64bit data type that is 8-byte aligned */
> 
> Expand this comment a bit that that using this type as a 
> replacement for u64 is recommended
> for any user visible 64bit value in a structure and that it 
> avoids problem with the compat layer on x86-64.
> 

Well yes, I was actually about to write that comment.  But it should
describe the compat problems fully?