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A BAR frame must be transmitted when an frame in an A-MPDU session fails to transmit - it's retried too often, or it can't be cloned for re-transmission. The BAR frame tells the remote side to advance the left edge of the block-ack window (BAW) to a new value. In order to do this: * TX for that particular node/TID must be paused; * The existing frames in the hardware queue needs to be completed, whether they're TXed successfully or otherwise; * The new left edge of the BAW is then communicated to the remote side via a BAR frame; * Once the BAR frame has been sucessfully TXed, aggregation can resume; * If the BAR frame can't be successfully TXed, the aggregation session is torn down. This is a first pass that implements the above. What needs to be done/ tested: * What happens during say, a channel reset / stuck beacon _and_ BAR TX. It _should_ be correctly buffered and retried once the reset has completed. But if a bgscan occurs (and they shouldn't, grr) the BAR frame will be forcibly failed and the aggregation session will be torn down. Yes, another reason to disable bgscan until I've figured this out. * There's way too much locking going on here. I'm going to do a couple of further passes of sanitising and refactoring so the (re) locking isn't so heavy. Right now I'm going for correctness, not speed. * The BAR TX can fail if the hardware TX queue is full. Since there's no "free" space kept for management frames, a full TX queue (from eg an iperf test) can race with your ability to allocate ath_buf/mbufs and cause issues. I'll knock this on the head with a subsequent commit. * I need to do some _much_ more thorough testing in hostap mode to ensure that many concurrent traffic streams to different end nodes are correctly handled. I'll find and squish whichever bugs show up here. But, this is an important step to being able to flip on 802.11n by default. The last issue (besides bug fixes, of course) is HT frame protection and I'll address that in a subsequent commit.
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