On 11/02/2011 10:49 AM, Johannes Berg wrote:
On Wed, 2011-11-02 at 09:59 -0700, Ben Greear wrote:
No. Neither of these can ever be increased so it's not that simple. And
making it smaller is always possible since it's just advertising.
Presumably you do understand the reasons for this advertising/these
restrictions?
It seems that a driver might default to a mid-range value for the MPDU values
because it is somehow 'better' for whatever reason, and yet it might still
support larger values if the user desires, perhaps because in specific
scenarios larger values are better. Ath9k does set to the max value,
so if we do a per-driver capabilities flag as I did in v2 then we
are safe.
Then the proper way to do that would be to not have a flag, but a max it
can be set to. However, I see no reason it should default to a mid-range
value?! iwlwifi for example needs to allocate enough space but ... I
don't get it. What's wrong with simply not allowing to increase, only
decrease?
Ok, I'll work on allowing the value to only be decreased.
I should be able to compare against whatever the hardware set in
the channel ht-info I think.
/* add attributes here, update the policy in nl80211.c */
I copied some of that code from nl80211_set_station, which appears to
also forget to check the length for the NL80211_ATTR_HT_CAPABILITY
object. Is there some reason why it doesn't need to check, or does
that code need fixing as well?
NL80211_ATTR_HT_CAPABILITY in particular *has* a policy entry.
Ahh, I didn't realize that's what was meant by policy. Mind if
I change that comment to something like what is below?
/* add attributes here, update the nl80211_policy array in nl80211.c */
From 20.1.1 of the 802.11n spec:
"An HT non-AP STA shall support all equal modulation (EQM) rates for one spatial stream (MCSs 0 through
7) using 20 MHz channel width. An HT AP shall support all EQM rates for one and two spatial streams
(MCSs 0 through 15) using 20 MHz channel width."
That is why I wrote that code as I did, but perhaps I misunderstand that section of
the docs.
No, that makes some sense, I wasn't aware of that restriction.
Well, personally it seems like a lame restriction, and at least hostapd and ath9k will
deal fine with a station advertising less than that, but probably best to
stick with the spec if possible.
Thanks,
Ben
--
Ben Greear <greearb@xxxxxxxxxxxxxxx>
Candela Technologies Inc http://www.candelatech.com
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