Re: [PATCH] sector_t overflow in block layer

[Linus Torvalds]

On Thu, 18 May 2006, Andreas Dilger wrote:
>  	struct bio *bio;
> +	unsigned long long sector;
>  	int ret = 0;
>  
>  	BUG_ON(!buffer_locked(bh));
>  	BUG_ON(!buffer_mapped(bh));
>  	BUG_ON(!bh->b_end_io);
>  
> +	/* Check if we overflow sector_t when computing the sector offset.  */
> +	sector = (unsigned long long)bh->b_blocknr * (bh->b_size >> 9);

Ok so far, looks fine.

But what the heck is this:

> +#if !defined(CONFIG_LBD) && BITS_PER_LONG == 32
> +	if (unlikely(sector != (sector_t)sector))
> +#else
> +	if (unlikely(((bh->b_blocknr >> 32) * (bh->b_size >> 9)) >=
> +		     0xffffffff00000000ULL))
> +#endif

I don't understand the #ifdef at all.

Why isn't that just a 

	if (unlikely(sector != (sector_t)sector))

and that's it? What does this have to do with CONFIG_LBD or BITS_PER_LONG, 
or anything at all?

If the sector number fits in a sector_t, we're all good.

			Linus
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