Re: [PATCH] bitmap: separate bitmap parsing for user buffer and kernelbuffer

[H. Peter Anvin]

Andrew Morton wrote:
> On Wed, 4 Oct 2006 17:56:30 -0700
> Reinette Chatre <reinette.chatre@xxxxxxxxxxxxxxx> wrote:
>
> > +			if (is_user) {
> > +				if (__get_user(c, buf++))
> > +					return -EFAULT;
> > +			}
> > +			else
> > +				c = *buf++;
>
> Is this actually needed?  __get_user(kernel_address) works OK and (believe
> it or not, given all the stuff it involves) boils down to a single instruction.		

On some architectures, kernel and user space are separate, overlapping 
address spaces.

If __bitmap_parse was an inline (and not exported), this would be okay; 
as it is, you end up doing the test dynamically under all circumstances, 
even though in most (if not all) cases the address space is know a priori.

	-hpa
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/