linux-kernel - Re: [PATCH] utilities: add helper functions for safe 64-bit integer operations as 32-bit halves

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Message-ID: <20070422091816.GC1558@infradead.org>
Date:	Sun, 22 Apr 2007 10:18:16 +0100
From:	Christoph Hellwig <hch@...radead.org>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Alan Cox <alan@...rguk.ukuu.org.uk>,
	"John Anthony Kazos Jr." <jakj@...-k-j.com>,
	James Bottomley <James.Bottomley@...elEye.com>,
	"Cameron, Steve" <Steve.Cameron@...com>,
	"Miller, Mike (OS Dev)" <Mike.Miller@...com>,
	Hisashi Hifumi <hifumi.hisashi@....ntt.co.jp>,
	jens.axboe@...cle.com, linux-kernel@...r.kernel.org,
	linux-scsi@...r.kernel.org, trivial@...nel.org
Subject: Re: [PATCH] utilities: add helper functions for safe 64-bit integer operations as 32-bit halves

On Sat, Apr 21, 2007 at 02:06:22PM -0700, Andrew Morton wrote:
> On Sat, 21 Apr 2007 22:01:47 +0100 Alan Cox <alan@...rguk.ukuu.org.uk> wrote:
> 
> > > > +#define lower_32_bits(n) (sizeof(n) == 8 ? (u32)(n) : (n))
> > > 
> > > n&0xffffffff would be simpler.
> > > 
> > > Do we actually have any call for this?
> > 
> > The only case for all of this we care about is sector_t, which is one
> > type, with specific properties (eg always being positive). The rest is
> > over-engineering. Call it sector_upper32() do it the simple way and stop
> > trying to solve a problem we don't have
> 
> James said we have the same problem with dma_addr_t.

Yes.  It's in fact the far more common case and we have a bread of
macros dealing with the issue in various drivers.
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