[RFC] WARNING: at net/mac80211/ieee80211_rate.h:159 rate_lowest_index()

[Vladimir Koutny <vlado@work.ksp.sk>]

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Hi,
the warning in $subj can pop up in the following scenario:

- iwconfig wlan0 mode ad-hoc; ifconfig wlan0 up
- a frame arrives from an unknown station which triggers
  ieee80211_ibss_sta_add() (called from prepare_for_handlers())

In this case, we create a new sta entry, fill in supp_rates field,
initialize rate_control algo, and insert this sta entry into the list.

The problem is the assignment for supp_rates:

sta->supp_rates[local->hw.conf.channel->band] =
	sdata->u.sta.supp_rates_bits[local->hw.conf.channel->band];

because sdata->u.sta.supp_rates_bits is set only when we actually
join an ibss, which is not the case in this scenario; so we assign
zero here. Then, the code in rate_control_pid_rate_init() calls
rate_lowest_index() for some reason, and since no supported rate is
found, this warning is issued.


The question is how sta->supp_rates should be initialized:

- we could initialize it to our sta's rates, but then we could
  probably transmit to a station at unsupported rate

- add new ibss station only on received beacon, not on a data frame;
  currently, beacons are ignored for this purpose (they just update
  the bss list later on)

- something else (like 1Mbps only)?

As soon as we do sta_join_ibss(), this warning won't happen again.


Note that once we have sta entry (in our ibss), we will update its
supported rates based on beacons it sends (in rx_bss_info()).

Any thoughts?

Regards,
  Vlado


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