| // Copyright 2019 The Fuchsia Authors. All rights reserved. |
| // Use of this source code is governed by a BSD-style license that can be |
| // found in the LICENSE file. |
| |
| #include "src/connectivity/bluetooth/core/bt-host/l2cap/enhanced_retransmission_mode_tx_engine.h" |
| |
| #include <zircon/assert.h> |
| |
| #include <limits> |
| |
| #include "lib/async/default.h" |
| #include "src/connectivity/bluetooth/core/bt-host/common/log.h" |
| #include "src/connectivity/bluetooth/core/bt-host/l2cap/frame_headers.h" |
| |
| namespace bt::l2cap::internal { |
| |
| using Engine = EnhancedRetransmissionModeTxEngine; |
| |
| namespace { |
| |
| // Returns the number of frames within the range from |low| to |high|, inclusive |
| // of |low|, but exclusive of |high|. Returns zero if |low == high|. |
| uint8_t NumFramesBetween(uint8_t low, uint8_t high) { |
| if (high < low) { |
| high += (EnhancedControlField::kMaxSeqNum + 1); |
| } |
| return high - low; |
| } |
| |
| } // namespace |
| |
| Engine::EnhancedRetransmissionModeTxEngine(ChannelId channel_id, uint16_t max_tx_sdu_size, |
| uint8_t max_transmissions, uint8_t n_frames_in_tx_window, |
| SendFrameCallback send_frame_callback, |
| ConnectionFailureCallback connection_failure_callback) |
| : TxEngine(channel_id, max_tx_sdu_size, std::move(send_frame_callback)), |
| max_transmissions_(max_transmissions), |
| n_frames_in_tx_window_(n_frames_in_tx_window), |
| connection_failure_callback_(std::move(connection_failure_callback)), |
| expected_ack_seq_(0), |
| next_tx_seq_(0), |
| last_tx_seq_(0), |
| req_seqnum_(0), |
| retransmitted_range_during_poll_(false), |
| n_receiver_ready_polls_sent_(0), |
| remote_is_busy_(false) { |
| ZX_DEBUG_ASSERT(n_frames_in_tx_window_); |
| receiver_ready_poll_task_.set_handler([this] { |
| ZX_ASSERT(thread_checker_.is_thread_valid()); |
| SendReceiverReadyPoll(); |
| StartMonitorTimer(); |
| }); |
| monitor_task_.set_handler([this] { |
| ZX_ASSERT(thread_checker_.is_thread_valid()); |
| if (max_transmissions_ == 0 || n_receiver_ready_polls_sent_ < max_transmissions_) { |
| SendReceiverReadyPoll(); |
| StartMonitorTimer(); |
| } else { |
| connection_failure_callback_(); // May invalidate |self|. |
| } |
| }); |
| } |
| |
| bool Engine::QueueSdu(ByteBufferPtr sdu) { |
| ZX_ASSERT(thread_checker_.is_thread_valid()); |
| ZX_ASSERT(sdu); |
| // TODO(fxbug.dev/1033): Add support for segmentation |
| if (sdu->size() > max_tx_sdu_size_) { |
| bt_log(DEBUG, "l2cap", "SDU size exceeds channel TxMTU (channel-id: %#.4x)", channel_id_); |
| return false; |
| } |
| |
| const auto seq_num = GetNextTxSeq(); |
| SimpleInformationFrameHeader header(seq_num); |
| DynamicByteBuffer frame(sizeof(header) + sdu->size()); |
| auto body = frame.mutable_view(sizeof(header)); |
| frame.WriteObj(header); |
| sdu->Copy(&body); |
| |
| // TODO(fxbug.dev/1366): Limit the size of the queue. |
| pending_pdus_.push_back(std::move(frame)); |
| MaybeSendQueuedData(); |
| return true; |
| } |
| |
| void Engine::UpdateAckSeq(uint8_t new_seq, bool is_poll_response) { |
| ZX_ASSERT(thread_checker_.is_thread_valid()); |
| // TODO(quiche): Reconsider this assertion if we allow reconfiguration of the TX window. |
| ZX_DEBUG_ASSERT_MSG(NumUnackedFrames() <= n_frames_in_tx_window_, |
| "(NumUnackedFrames() = %u, n_frames_in_tx_window_ = %u, " |
| "expected_ack_seq_ = %u, last_tx_seq_ = %u)", |
| NumUnackedFrames(), n_frames_in_tx_window_, expected_ack_seq_, last_tx_seq_); |
| |
| const auto n_frames_acked = NumFramesBetween(expected_ack_seq_, new_seq); |
| if (n_frames_acked > NumUnackedFrames()) { |
| // Peer acknowledgment of our outbound data (ReqSeq) exceeds the sequence numbers of |
| // yet-acknowledged data that we've sent to that peer. See conditions "With-Invalid-ReqSeq" and |
| // "With-Invalid-ReqSeq-Retrans" in Core Spec v5.0 Vol 3 Part A Sec 8.6.5.5. |
| bt_log(WARN, "l2cap", |
| "Received acknowledgment for %hhu frames but only %hhu frames are pending", |
| n_frames_acked, NumUnackedFrames()); |
| connection_failure_callback_(); // May invalidate |self|. |
| return; |
| } |
| |
| // Perform Stop-MonitorTimer when "F = 1," per Core Spec v5.0, Vol 3, Part A, Sec 8.6.5.7–8. |
| if (is_poll_response) { |
| monitor_task_.Cancel(); |
| } |
| |
| ZX_ASSERT(!(range_request_.has_value() && single_request_.has_value())); |
| if (ProcessSingleRetransmitRequest(new_seq, is_poll_response) == |
| UpdateAckSeqAction::kConsumeAckSeq) { |
| return; |
| } |
| |
| auto n_frames_to_discard = n_frames_acked; |
| while (n_frames_to_discard) { |
| ZX_DEBUG_ASSERT(!pending_pdus_.empty()); |
| pending_pdus_.pop_front(); |
| --n_frames_to_discard; |
| } |
| |
| expected_ack_seq_ = new_seq; |
| if (expected_ack_seq_ == next_tx_seq_) { |
| receiver_ready_poll_task_.Cancel(); |
| } |
| |
| const auto range_request = std::exchange(range_request_, std::nullopt); |
| |
| // RemoteBusy is cleared as the first action to take when receiving a REJ per Core Spec v5.0 Vol |
| // 3, Part A, Sec 8.6.5.9–11, so their corresponding member variables shouldn't be both set. |
| ZX_ASSERT(!(range_request.has_value() && remote_is_busy_)); |
| bool should_retransmit = range_request.has_value(); |
| |
| // This implements the logic for RejActioned in the Recv {I,RR,REJ} (F=1) event for all of the |
| // receiver states (Core Spec v5.0 Vol 3, Part A, Sec 8.6.5.9–11). |
| if (is_poll_response) { |
| if (retransmitted_range_during_poll_) { |
| should_retransmit = false; |
| retransmitted_range_during_poll_ = false; |
| } else { |
| should_retransmit = true; |
| } |
| } |
| |
| if (remote_is_busy_) { |
| return; |
| } |
| |
| // This implements the logic for PbitOutstanding in the Recv REJ (F=0) event for all of the |
| // receiver states (Core Spec v5.0 Vol 3, Part A, Sec 8.6.5.9–11). |
| if (range_request.has_value() && !is_poll_response && monitor_task_.is_pending()) { |
| retransmitted_range_during_poll_ = true; |
| } |
| |
| if (should_retransmit) { |
| const bool set_is_poll_response = |
| range_request.value_or(RangeRetransmitRequest{}).is_poll_request; |
| if (RetransmitUnackedData(std::nullopt, set_is_poll_response).is_error()) { |
| return; |
| } |
| } |
| |
| MaybeSendQueuedData(); |
| |
| // TODO(quiche): Restart the receiver_ready_poll_task_, if there's any |
| // remaining unacknowledged data. |
| } |
| |
| void Engine::UpdateReqSeq(uint8_t new_seq) { |
| ZX_ASSERT(thread_checker_.is_thread_valid()); |
| req_seqnum_ = new_seq; |
| } |
| |
| void Engine::ClearRemoteBusy() { |
| ZX_ASSERT(thread_checker_.is_thread_valid()); |
| // TODO(quiche): Maybe clear backpressure on the Channel (subject to TxWindow contraints). |
| remote_is_busy_ = false; |
| } |
| |
| void Engine::SetRemoteBusy() { |
| ZX_ASSERT(thread_checker_.is_thread_valid()); |
| // TODO(fxbug.dev/1367): Signal backpressure to the Channel. |
| remote_is_busy_ = true; |
| receiver_ready_poll_task_.Cancel(); |
| } |
| |
| void Engine::SetSingleRetransmit(bool is_poll_request) { |
| ZX_ASSERT(thread_checker_.is_thread_valid()); |
| ZX_ASSERT(!single_request_.has_value()); |
| ZX_ASSERT(!range_request_.has_value()); |
| // Store SREJ state for UpdateAckSeq to handle. |
| single_request_ = SingleRetransmitRequest{.is_poll_request = is_poll_request}; |
| } |
| |
| void Engine::SetRangeRetransmit(bool is_poll_request) { |
| ZX_ASSERT(thread_checker_.is_thread_valid()); |
| ZX_ASSERT(!single_request_.has_value()); |
| ZX_ASSERT(!range_request_.has_value()); |
| // Store REJ state for UpdateAckSeq to handle. |
| range_request_ = RangeRetransmitRequest{.is_poll_request = is_poll_request}; |
| } |
| |
| void Engine::MaybeSendQueuedData() { |
| ZX_ASSERT(thread_checker_.is_thread_valid()); |
| if (remote_is_busy_ || monitor_task_.is_pending()) { |
| return; |
| } |
| |
| // Find the first PDU that has not already been transmitted (if any). |
| // * This is not necessarily the first PDU, because that may have been |
| // transmited already, and is just pending acknowledgement. |
| // * This is not necessarily the last PDU, because earlier PDUs may have been |
| // queued without having been sent over-the-air (due, e.g., to tx_window |
| // constraints). |
| // |
| // TODO(quiche): Consider if there's a way to do this that isn't O(n). |
| auto it = std::find_if(pending_pdus_.begin(), pending_pdus_.end(), |
| [](const auto& pending_pdu) { return pending_pdu.tx_count == 0; }); |
| |
| while (it != pending_pdus_.end() && NumUnackedFrames() < n_frames_in_tx_window_) { |
| ZX_DEBUG_ASSERT(it->tx_count == 0); |
| SendPdu(&*it); |
| last_tx_seq_ = it->buf.As<SimpleInformationFrameHeader>().tx_seq(); |
| ++it; |
| } |
| } |
| |
| Engine::UpdateAckSeqAction Engine::ProcessSingleRetransmitRequest(uint8_t new_seq, |
| bool is_poll_response) { |
| const auto single_request = std::exchange(single_request_, std::nullopt); |
| ZX_ASSERT(!(single_request.has_value() && remote_is_busy_)); |
| if (!single_request.has_value()) { |
| return UpdateAckSeqAction::kDiscardAcknowledged; |
| } |
| |
| // This implements the logic for SrejActioned=TRUE in the Recv SREJ (P=0) (F=1) event for all of |
| // the receiver states (Core Spec v5.0 Vol 3, Part A, Sec 8.6.5.9–11). |
| if (is_poll_response && retransmitted_single_during_poll_.has_value() && |
| new_seq == *retransmitted_single_during_poll_) { |
| // Only a SREJ (F=1) with a matching AckSeq can clear this state, so if this duplicate |
| // suppression isn't performed it sticks around even when we sent the next poll request. |
| // AckSeq is modulo kMaxSeqNum + 1 so it'll roll over and potentially suppress retransmission |
| // of a different (non-duplicate) packet in a later poll request-response cycle. Unfortunately |
| // this isn't fixed as of Core Spec v5.2 so it's implemented as written. |
| retransmitted_single_during_poll_.reset(); |
| |
| // Return early to suppress duplicate retransmission. |
| return UpdateAckSeqAction::kConsumeAckSeq; |
| } |
| |
| // This implements the logic for PbitOutstanding in the Recv SREJ (P=0) (F=0) and Recv SREJ(P=1) |
| // events for all of the receiver states (Core Spec v5.0 Vol 3, Part A, Sec 8.6.5.9–11). |
| if (!is_poll_response && monitor_task_.is_pending()) { |
| retransmitted_single_during_poll_ = new_seq; |
| } |
| |
| if (RetransmitUnackedData(new_seq, single_request->is_poll_request).is_error()) { |
| return UpdateAckSeqAction::kConsumeAckSeq; |
| } |
| |
| // Only "single requests" that are poll requests acknowledge previous I-Frames and cause initial |
| // transmission of queued SDUs, per Core Spec v5.0, Vol 3, Part A, Sec 8.6.1.4. |
| if (single_request->is_poll_request) { |
| return UpdateAckSeqAction::kDiscardAcknowledged; |
| } |
| return UpdateAckSeqAction::kConsumeAckSeq; |
| } |
| |
| void Engine::StartReceiverReadyPollTimer() { |
| ZX_DEBUG_ASSERT(!monitor_task_.is_pending()); |
| n_receiver_ready_polls_sent_ = 0; |
| receiver_ready_poll_task_.Cancel(); |
| receiver_ready_poll_task_.PostDelayed(async_get_default_dispatcher(), |
| kErtmReceiverReadyPollTimerDuration); |
| } |
| |
| void Engine::StartMonitorTimer() { |
| ZX_DEBUG_ASSERT(!receiver_ready_poll_task_.is_pending()); |
| monitor_task_.Cancel(); |
| monitor_task_.PostDelayed(async_get_default_dispatcher(), kErtmMonitorTimerDuration); |
| } |
| |
| void Engine::SendReceiverReadyPoll() { |
| SimpleReceiverReadyFrame frame; |
| frame.set_receive_seq_num(req_seqnum_); |
| frame.set_is_poll_request(); |
| ++n_receiver_ready_polls_sent_; |
| ZX_ASSERT_MSG(max_transmissions_ == 0 || n_receiver_ready_polls_sent_ <= max_transmissions_, |
| "(n_receiver_ready_polls_sent_ = %u, " |
| "max_transmissions = %u)", |
| n_receiver_ready_polls_sent_, max_transmissions_); |
| send_frame_callback_(std::make_unique<DynamicByteBuffer>(BufferView(&frame, sizeof(frame)))); |
| } |
| |
| uint8_t Engine::GetNextTxSeq() { |
| auto ret = next_tx_seq_; |
| ++next_tx_seq_; |
| if (next_tx_seq_ > EnhancedControlField::kMaxSeqNum) { |
| next_tx_seq_ = 0; |
| } |
| return ret; |
| } |
| |
| uint8_t Engine::NumUnackedFrames() { |
| if (pending_pdus_.empty()) { |
| // Initially, |ack_seqnum_ == last_tx_seq_ == 0|, but the number of |
| // unacknowledged frames is 0, not 1. |
| return 0; |
| } else if (pending_pdus_.front().tx_count == 0) { |
| // While we have some data queued, none of that data has been sent |
| // over-the-air. This might happen, e.g., transiently in QueueSdu(). |
| return 0; |
| } else { |
| // Having ascertained that some data _is_ in flight, the number of frames in |
| // flight is given by the expression below. |
| return NumFramesBetween(expected_ack_seq_, |
| last_tx_seq_ + 1 // Include frame with |last_tx_seq_| in count |
| ); |
| } |
| } |
| |
| void Engine::SendPdu(PendingPdu* pdu) { |
| ZX_DEBUG_ASSERT(pdu); |
| pdu->buf.AsMutable<SimpleInformationFrameHeader>().set_receive_seq_num(req_seqnum_); |
| |
| // Prevent tx_count from overflowing to zero, as that would be indistinguishable from "never |
| // transmitted." This is only possible when configured for infinite retransmissions, so there is |
| // no benefit to having an accurate tx_count after each frame's initial transmission. |
| if (pdu->tx_count != std::numeric_limits<decltype(pdu->tx_count)>::max()) { |
| pdu->tx_count++; |
| } |
| StartReceiverReadyPollTimer(); |
| send_frame_callback_(std::make_unique<DynamicByteBuffer>(pdu->buf)); |
| } |
| |
| fit::result<> Engine::RetransmitUnackedData(std::optional<uint8_t> only_with_seq, |
| bool set_is_poll_response) { |
| // The receive engine should have cleared the remote busy condition before |
| // calling any method that would cause us (the transmit engine) to retransmit |
| // unacked data. See, e.g., Core Spec v5.0, Volume 3, Part A, Table 8.6, row |
| // "Recv REJ (F=0)". |
| ZX_DEBUG_ASSERT(!remote_is_busy_); |
| |
| // Any peer actions that cause retransmission indicate the peer is alive. This is in conflict with |
| // Core Spec v5.0, Vol 3, Part A, Sec 8.6.5.8, which only stops the MonitorTimer when a poll |
| // response is received and omits what to do when REJ or SREJ cause retransmission. However, this |
| // behavior of canceling the MonitorTimer "early" is in line with Sequence Diagram Fig 4.94, L2CAP |
| // Test Spec v5.0.2 Section 4.9.7.24, among others that show REJ or SREJ causing the receiver to |
| // cancel its MonitorTimer. We follow the latter behavior because (1) it's less ambiguous (2) it |
| // makes sense and (3) we need to pass those tests. |
| monitor_task_.Cancel(); |
| |
| const auto n_to_send = NumUnackedFrames(); |
| ZX_ASSERT(n_to_send <= n_frames_in_tx_window_); |
| ZX_DEBUG_ASSERT(n_to_send <= pending_pdus_.size()); |
| |
| auto cur_frame = pending_pdus_.begin(); |
| auto last_frame = std::next(cur_frame, n_to_send); |
| for (; cur_frame != last_frame; cur_frame++) { |
| ZX_DEBUG_ASSERT(cur_frame != pending_pdus_.end()); |
| |
| const auto control_field = cur_frame->buf.As<SimpleInformationFrameHeader>(); |
| if (only_with_seq.has_value() && control_field.tx_seq() != *only_with_seq) { |
| continue; |
| } |
| |
| // Core Spec v5.0, Vol 3, Part A, Sec 5.4: "In Enhanced Retransmission mode a value of zero for |
| // MaxTransmit means infinite retransmissions." |
| if (max_transmissions_ != 0 && cur_frame->tx_count >= max_transmissions_) { |
| ZX_ASSERT_MSG(cur_frame->tx_count == max_transmissions_, "%hhu != %hhu", cur_frame->tx_count, |
| max_transmissions_); |
| connection_failure_callback_(); |
| return fit::error(); |
| } |
| |
| if (set_is_poll_response) { |
| cur_frame->buf.AsMutable<EnhancedControlField>().set_is_poll_response(); |
| |
| // Per "Retransmit-I-frames" of Core Spec v5.0 Vol 3, Part A, Sec 8.6.5.6, "[t]he F-bit of all |
| // other [than the first] unacknowledged I-frames sent shall be 0," so clear this for |
| // subsequent iterations. |
| set_is_poll_response = false; |
| } |
| |
| // TODO(fxbug.dev/1453): If the task is already running, we should not restart it. |
| SendPdu(&*cur_frame); |
| cur_frame->buf.AsMutable<EnhancedControlField>() = control_field; |
| } |
| |
| return fit::ok(); |
| } |
| |
| } // namespace bt::l2cap::internal |