Am Mittwoch, 7. Februar 2007 19:23 schrieb David Brownell:
> On Wednesday 07 February 2007 4:25 am, Oliver Neukum wrote:
>
> > 1. Disallow any padding
> > 2. Assume the structure may be in unaligned memory
> >
> > Issue number #1 is usually handled by the USB specification.
>
> Key word "usually"; they haven't AFAIK promised to do so.
True. For descriptors it doesn't really matter much.
> > #2 is not. Therefore packed data structures will make inferior code
> > even in the case we alloc the data structure ourselves.
[..]
> Are you honestly suggesting the performance impact of this could posssibly
> outweigh the maintainence nightmare of needing to explicitly code unaligned
> access into all the kernel and userspace code that touches descriptor fields?
As long as you leave alone the control requests I am all in favor of packed.
Regards
Oliver
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