Re: [RFC] mac80211: fix short preamble determination

[Johannes Berg <johannes@sipsolutions.net>]

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On Mon, 2008-10-13 at 18:59 +0300, Jouni Malinen wrote:

> > -	if (ieee80211_is_data(hdr->frame_control) &&
> > -	    tx->sdata->vif.bss_conf.use_short_preamble &&
> > -	    (!tx->sta || test_sta_flags(tx->sta, WLAN_STA_SHORT_PREAMBLE)))
> > +	if (tx->sdata->vif.bss_conf.use_short_preamble &&
> > +	    (ieee80211_is_data(hdr->frame_control) ||
> > +	     (tx->sta && test_sta_flags(tx->sta, WLAN_STA_SHORT_PREAMBLE)))
> 
> Changing '!tx->sta ||' to 'tx->sta &&' sounds reasonable, but I'm not so
> sure about the other change.. In theory, short preamble is negotiated
> per STA and while we do current disable short preamble completely in the
> BSS if a non-short-preamble-capable STA associates, I'm not sure whether
> that would be an absolute requirement.

I don't see how it cannot be -- you need stations not capable of
short-preamble to correctly update their NAV, no?

> As far as management frames
> (e.g., Probe Response) are concerned, IEEE 802.11-2007 18.2.2.2 has an
> interesting statement: "all management traffic is returned with the same
> type preamble as received". I have not been able to find normative
> requirement for that being the case, though.

Yeah, I found that statement too, but no other information on it either,
heh. Not that we can actually support that easily at all. And besides,
it would be kinda weird to send probe _requests_ with short preamble to
start with, since then you wouldn't find APs w/o short preamble...

johannes

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