Re: [PATCH] mac80211: support adding IV-room in the skb for CCMP keys

[Johannes Berg <johannes@sipsolutions.net>]

On Mon, 2012-05-07 at 14:01 +0200, Janusz Dziedzic wrote:
> 2011/10/26 Arik Nemtsov <arik@wizery.com>:
> > On Wed, Oct 26, 2011 at 11:59, Johannes Berg <johannes@sipsolutions.net> wrote:
> >> On 10/23/2011 8:21 AM, Arik Nemtsov wrote:
> >>>
> >>> Some cards can generate CCMP IVs in HW, but require the space for the IV
> >>> to be pre-allocated in the frame at the correct offset. Add a key flag
> >>> that allows us to achieve this.
> >>
> >> Is it really that expensive to generate the IV and then not use it that this
> >> is worth the extra complexity? This not just makes it more complex but also
> >> more expensive in the other case.
> >>
> >
> > Some of the platforms with this chip are pretty weak (host CPU is the
> > bottleneck).
> >
> > We add another "if" for the other case (for a value that's likely in
> > the cacheline already). I don't think that's too bad.
> >
> 
> Hello,
> Why this is only done for CCMP?
> Our firmware require such IVs allocation for all modes and currently
> we have common code that do that in the driver based on:
> iv_len = tx_info->control.hw_key->iv_len
> icv_len = tx_info->control.hw_key->icv_len
> 
> /* cw1200 driver */
> skb_push(t->skb, iv_len);
> memmove(newhdr, newhdr + iv_len, t->hdrlen);
> skb_put(t->skb, icv_len);
> ....
> 
> Isn't better to handle all modes in mac80211 base on
> IEEE80211_KEY_FLAG_PUT_IV_SPACE or just leave this for the driver?
> 
> I know this is easy to fix in our driver but still we have to remember
> that in case of CCMP mac80211 will already do it for us and will not
> do that in case of other modes.
> So, my proposal is to remove all changes from net/mac80211/wpa.c file
> and remember that driver should care about it - in such case
> PUT_IV_SPACE will be more generic.

I suggest the opposite, make it more generic in mac80211.

johannes