2009/4/15 Gábor Stefanik <netrolller.3d@xxxxxxxxx>:
> 2009/4/15 Johannes Berg <johannes@xxxxxxxxxxxxxxxx>:
>> On Wed, 2009-04-15 at 00:34 +0200, Gábor Stefanik wrote:
>>> Set the total count of TX tries to 1 if IEEE80211_TX_CTL_NO_ACK is
>>> set. This fixes a bug where mac80211 allowed the RC algo to request
>>> drivers to forcibly retransmit NO_ACK (e.g. multicast) frames until
>>> the excessive-retries limit is reached.
>>
>> Why not fix the rate control algorithms to use the no-ack flag instead
>> of is_multicast?
>
> I was thinking about that originally, but we have 5 RC algorithms
> (minstrel, pid, iwl-3945-rs, iwl-agn-rs & ath9k-rs) right now, with
> possibly more to come for future N-based devices. Fixing them all
> one-by-one would be much more tedious, and we will still not be
> future-proof (that is, there is always the risk of getting a new
> driver released with its own, specific RC algorithm that suffers from
> this bug). This way, if e.g. Whatevercom releases a driver for its
> WhateWIFI UltraMIMO1337 chipset with its own, buggy "whatever-rs"
> algorithm, NO_ACK will still work properly for that driver.
BTW, Minstrel specifically forces NO_ACK packets to be retried the
maximal allowed number of times.
rc80211_minstrel.c, line 246:
> if (!sta || !mi || use_low_rate(skb)) {
> ar[0].idx = rate_lowest_index(sband, sta);
> ar[0].count = mp->max_retry;
> return;
> }
mp->max_retry = hw->max_rate_tries, or 7 if hw->max_rate_tries is 0.
The use_low_rate function is basically a check for NO_ACK.
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