Re: + expose-range-checking-functions-from-arch-specific.patch added to -mm tree

[Rusty Russell <rusty@rustcorp.com.au>]

On Tue, 2007-04-10 at 19:48 -0700, Andrew Morton wrote:
> On Wed, 11 Apr 2007 12:19:10 +1000 Rusty Russell <rusty@rustcorp.com.au> wrote:
> > > > + * Like val + len > limit, except with overflow checking.
> > > > + */
> > > > +static inline bool val_outside(unsigned long val, unsigned long len,
> > > > +			       unsigned long limit)
> > > > +
> > > > +{
> > > > +	return val + len > limit || val + len < val;

> I probably shouldn't look at this after a glass of red, but otoh, perhaps
> that's a good way of ensuring that we have a built-in margin.

> I find this function incomprehensible.  I'd just avoid using the sorry
> thing, personally.

No, you're absolutely right.  Naming is vital, and something I criticise
others for regularly.  We don't say "that is incomprehensible" anywhere
near often enough 8(

Is this clearer?

static inline bool range_over_limit(unsigned long start,
				    unsigned long len,
				    unsigned long limit)
{
	return start + len > limit || start + len < start;
}

Cheers,
Rusty.
PS.  Previously this identical function was called __range_ok() (and
returned 0 if it was not ok...)