Wifi rate control

FreeBSD has the beginnings of a rate control API that was primarily designed for pre-11n networks. It provides a simple API for rate control management and lookups.

The main API code is in sys/net80211/ieee80211_rate.[ch] . The three implemented modules so far:

• ieee80211_none;
• ieee80211_rssadapt;
• ieee80211_amrr .

TODO

• Update the rate / tx_complete / tx_update API to take a struct with counters / statistics. This should include time taken, short (RTS/CTS) and long (ACK) retries, success/failure, later A-MPDU BAR TX success information, current RSSI, perhaps even EVM.
• Both tx_complete and tx_update should be provided by each rate control module.
• Update the rate API to return the rate information as a struct, rather than the rix. Most drivers end up referencing ni→tx_rate anyway, rather than using the returned information.
• Teach the rate API more about the packet being scheduled - eg is it multicast? what's the length? Is it A-MPDU / A-MSDU?
• Figure out what to do about locking.

• There's only two real modules.
• The API use differs between modules and drivers. This should be unified.
• amrr has some basic 11n awareness - enough for iwn to make cursory use of it. It should grow a lot more features.