Re: rfc: "canonical" radiotap parser

[David Young <dyoung-e+AXbWqSrlAAvxtiuMwx3w@public.gmane.org>]

On Mon, Dec 10, 2007 at 01:37:30PM +0100, Johannes Berg wrote:
> 
> > I was trying to give the compiler a hint to help it generate better
> > code on architectures, such as ARM, where unaligned loads may take
> > many instructions.
> 
> Well, yes, but who guarantees that it actually *is* aligned that way?
> Radiotap only specifies that the fields are aligned with respect to the
> start of the header, but there's nothing that guarantees alignment of
> that.

The caller of radiotap_parse_first() must supply a 64-bit aligned
ieee80211_radiotap_header in the first argument.  If the header is not
so aligned, then the parse fails right away with RADIOTAP_ERROR_ALIGNMENT.

Really, radiotap_parse_first() should require either 32-bit alignment,
or alignment as great as the maximum alignment of all of the fields that
are present, whichever is greater.

I copy radiotap headers to ensure 64-bit alignment in
main.c:cap_cb().

Dave

-- 
David Young             OJC Technologies
dyoung-eZodSLrBbDpBDgjK7y7TUQ@public.gmane.org      Urbana, IL * (217) 278-3933 ext 24