On Mon, Aug 17, 2009 at 11:03:44PM +0530, Rabin Vincent wrote:
> On Sat, Aug 15, 2009 at 07:17:11PM +0100, Russell King - ARM Linux wrote:
> > +#ifndef CONFIG_SPARSEMEM
> > +int pfn_valid(unsigned long pfn)
> > +{
> > + struct meminfo *mi = &meminfo;
> > + unsigned int mid, left = 0, right = mi->nr_banks;
> > +
> > + while ((mid = (right - left) / 2) > 0) {
> > + struct membank *bank = &mi->bank[mid];
> > +
> > + if (pfn < bank_pfn_start(bank))
> > + right = mid;
> > + else if (pfn >= bank_pfn_end(bank))
> > + left = mid + 1;
> > + else
> > + return 1;
> > + }
> > + return 0;
> > +}
> > +EXPORT_SYMBOL(pfn_valid);
> > +#endif
>
> The above function will ignore the first bank. I don't think that was
> intended.
Why do you say that?
Let's start with 4 membank entries - 0 1 2 3.
0 covers 0-10, 1 covers 20-30, 2 covers 40-50 and 3 covers 60-70.
Let's run through the steps looking for 5:
Initally, left = 0, right = 4, so mid=2. 5 < 40? Yes, so right becomes 2.
left = 0, right = 2, so mid=1. 5 < 20? Yes, so right becomes 1.
left = 0, right = 1, so mid=0. 5 < 0? No. 5 >= 10? No. so return 1.
This doesn't look to me like it ignores the first bank. I think you're
wrong. Please provide me with your proof ASAP because right now it's
pending for Linus.
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