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Diffstat (limited to 'src/core/or/congestion_control_flow.c')
| -rw-r--r-- | src/core/or/congestion_control_flow.c | 710 |
1 files changed, 710 insertions, 0 deletions
diff --git a/src/core/or/congestion_control_flow.c b/src/core/or/congestion_control_flow.c new file mode 100644 index 0000000000..805654664c --- /dev/null +++ b/src/core/or/congestion_control_flow.c @@ -0,0 +1,710 @@ +/* Copyright (c) 2019-2021, The Tor Project, Inc. */ +/* See LICENSE for licensing information */ + +/** + * \file congestion_control_flow.c + * \brief Code that implements flow control for congestion controlled + * circuits. + */ + +#define TOR_CONGESTION_CONTROL_FLOW_PRIVATE + +#include "core/or/or.h" + +#include "core/or/relay.h" +#include "core/mainloop/connection.h" +#include "core/or/connection_edge.h" +#include "core/mainloop/mainloop.h" +#include "core/or/congestion_control_common.h" +#include "core/or/congestion_control_flow.h" +#include "core/or/congestion_control_st.h" +#include "core/or/circuitlist.h" +#include "core/or/trace_probes_cc.h" +#include "feature/nodelist/networkstatus.h" +#include "trunnel/flow_control_cells.h" + +#include "core/or/connection_st.h" +#include "core/or/cell_st.h" +#include "app/config/config.h" + +/** Cache consensus parameters */ +static uint32_t xoff_client; +static uint32_t xoff_exit; + +static uint32_t xon_change_pct; +static uint32_t xon_ewma_cnt; +static uint32_t xon_rate_bytes; + +/* In normal operation, we can get a burst of up to 32 cells before returning + * to libevent to flush the outbuf. This is a heuristic from hardcoded values + * and strange logic in connection_bucket_get_share(). */ +#define MAX_EXPECTED_CELL_BURST 32 + +/* The following three are for dropmark rate limiting. They define when we + * scale down our XON, XOFF, and xmit byte counts. Early scaling is beneficial + * because it limits the ability of spurious XON/XOFF to be sent after large + * amounts of data without XON/XOFF. At these limits, after 10MB of data (or + * more), an adversary can only inject (log2(10MB)-log2(200*500))*100 ~= 1000 + * cells of fake XOFF/XON before the xmit byte count will be halved enough to + * triggering a limit. */ +#define XON_COUNT_SCALE_AT 200 +#define XOFF_COUNT_SCALE_AT 200 +#define ONE_MEGABYTE (UINT64_C(1) << 20) +#define TOTAL_XMIT_SCALE_AT (10 * ONE_MEGABYTE) + +/** + * Return the congestion control object of the given edge connection. + * + * Returns NULL if the edge connection doesn't have a cpath_layer or not + * attached to a circuit. But also if the cpath_layer or circuit doesn't have a + * congestion control object. + */ +static inline const congestion_control_t * +edge_get_ccontrol(const edge_connection_t *edge) +{ + if (edge->cpath_layer) + return edge->cpath_layer->ccontrol; + else if (edge->on_circuit) + return edge->on_circuit->ccontrol; + else + return NULL; +} + +/** + * Update global congestion control related consensus parameter values, every + * consensus update. + * + * More details for each of the parameters can be found in proposal 324, + * section 6.5 including tuning notes. + */ +void +flow_control_new_consensus_params(const networkstatus_t *ns) +{ +#define CC_XOFF_CLIENT_DFLT 500 +#define CC_XOFF_CLIENT_MIN 1 +#define CC_XOFF_CLIENT_MAX 10000 + xoff_client = networkstatus_get_param(ns, "cc_xoff_client", + CC_XOFF_CLIENT_DFLT, + CC_XOFF_CLIENT_MIN, + CC_XOFF_CLIENT_MAX)*RELAY_PAYLOAD_SIZE; + +#define CC_XOFF_EXIT_DFLT 500 +#define CC_XOFF_EXIT_MIN 1 +#define CC_XOFF_EXIT_MAX 10000 + xoff_exit = networkstatus_get_param(ns, "cc_xoff_exit", + CC_XOFF_EXIT_DFLT, + CC_XOFF_EXIT_MIN, + CC_XOFF_EXIT_MAX)*RELAY_PAYLOAD_SIZE; + +#define CC_XON_CHANGE_PCT_DFLT 25 +#define CC_XON_CHANGE_PCT_MIN 1 +#define CC_XON_CHANGE_PCT_MAX 99 + xon_change_pct = networkstatus_get_param(ns, "cc_xon_change_pct", + CC_XON_CHANGE_PCT_DFLT, + CC_XON_CHANGE_PCT_MIN, + CC_XON_CHANGE_PCT_MAX); + +#define CC_XON_RATE_BYTES_DFLT (500) +#define CC_XON_RATE_BYTES_MIN (1) +#define CC_XON_RATE_BYTES_MAX (5000) + xon_rate_bytes = networkstatus_get_param(ns, "cc_xon_rate", + CC_XON_RATE_BYTES_DFLT, + CC_XON_RATE_BYTES_MIN, + CC_XON_RATE_BYTES_MAX)*RELAY_PAYLOAD_SIZE; + +#define CC_XON_EWMA_CNT_DFLT (2) +#define CC_XON_EWMA_CNT_MIN (1) +#define CC_XON_EWMA_CNT_MAX (100) + xon_ewma_cnt = networkstatus_get_param(ns, "cc_xon_ewma_cnt", + CC_XON_EWMA_CNT_DFLT, + CC_XON_EWMA_CNT_MIN, + CC_XON_EWMA_CNT_MAX); +} + +/** + * Send an XOFF for this stream, and note that we sent one + */ +static void +circuit_send_stream_xoff(edge_connection_t *stream) +{ + xoff_cell_t xoff; + uint8_t payload[CELL_PAYLOAD_SIZE]; + ssize_t xoff_size; + + memset(&xoff, 0, sizeof(xoff)); + memset(payload, 0, sizeof(payload)); + + xoff_cell_set_version(&xoff, 0); + + if ((xoff_size = xoff_cell_encode(payload, CELL_PAYLOAD_SIZE, &xoff)) < 0) { + log_warn(LD_BUG, "Failed to encode xon cell"); + return; + } + + if (connection_edge_send_command(stream, RELAY_COMMAND_XOFF, + (char*)payload, (size_t)xoff_size) == 0) { + stream->xoff_sent = true; + } +} + +/** + * Compute the recent drain rate (write rate) for this edge + * connection and return it, in KB/sec (1000 bytes/sec). + * + * Returns 0 if the monotime clock is busted. + */ +static inline uint32_t +compute_drain_rate(const edge_connection_t *stream) +{ + if (BUG(!is_monotime_clock_reliable())) { + log_warn(LD_BUG, "Computing drain rate with stalled monotime clock"); + return 0; + } + + uint64_t delta = monotime_absolute_usec() - stream->drain_start_usec; + + if (delta == 0) { + log_warn(LD_BUG, "Computing stream drain rate with zero time delta"); + return 0; + } + + /* Overflow checks */ + if (stream->prev_drained_bytes > INT32_MAX/1000 || /* Intermediate */ + stream->prev_drained_bytes/delta > INT32_MAX/1000) { /* full value */ + return INT32_MAX; + } + + /* kb/sec = bytes/usec * 1000 usec/msec * 1000 msec/sec * kb/1000bytes */ + return MAX(1, (uint32_t)(stream->prev_drained_bytes * 1000)/delta); +} + +/** + * Send an XON for this stream, with appropriate advisory rate information. + * + * Reverts the xoff sent status, and stores the rate information we sent, + * in case it changes. + */ +static void +circuit_send_stream_xon(edge_connection_t *stream) +{ + xon_cell_t xon; + uint8_t payload[CELL_PAYLOAD_SIZE]; + ssize_t xon_size; + + memset(&xon, 0, sizeof(xon)); + memset(payload, 0, sizeof(payload)); + + xon_cell_set_version(&xon, 0); + xon_cell_set_kbps_ewma(&xon, stream->ewma_drain_rate); + + if ((xon_size = xon_cell_encode(payload, CELL_PAYLOAD_SIZE, &xon)) < 0) { + log_warn(LD_BUG, "Failed to encode xon cell"); + return; + } + + /* Store the advisory rate information, to send advisory updates if + * it changes */ + stream->ewma_rate_last_sent = stream->ewma_drain_rate; + + if (connection_edge_send_command(stream, RELAY_COMMAND_XON, (char*)payload, + (size_t)xon_size) == 0) { + /* Revert the xoff sent status, so we can send another one if need be */ + stream->xoff_sent = false; + } +} + +/** + * Process a stream XOFF, parsing it, and then stopping reading on + * the edge connection. + * + * Record that we have recieved an xoff, so we know not to resume + * reading on this edge conn until we get an XON. + * + * Returns false if the XOFF did not validate; true if it does. + */ +bool +circuit_process_stream_xoff(edge_connection_t *conn, + const crypt_path_t *layer_hint, + const cell_t *cell) +{ + (void)cell; + bool retval = true; + + if (BUG(!conn)) { + log_fn(LOG_PROTOCOL_WARN, LD_EDGE, + "Got XOFF on invalid stream?"); + return false; + } + + /* Make sure this XOFF came from the right hop */ + if (layer_hint && layer_hint != conn->cpath_layer) { + log_fn(LOG_PROTOCOL_WARN, LD_EDGE, + "Got XOFF from wrong hop."); + return false; + } + + if (edge_get_ccontrol(conn) == NULL) { + log_fn(LOG_PROTOCOL_WARN, LD_EDGE, + "Got XOFF for non-congestion control circuit"); + return false; + } + + if (conn->xoff_received) { + log_fn(LOG_PROTOCOL_WARN, LD_EDGE, + "Got multiple XOFF on connection"); + return false; + } + + /* If we are near the max, scale everything down */ + if (conn->num_xoff_recv == XOFF_COUNT_SCALE_AT) { + log_info(LD_EDGE, "Scaling down for XOFF count: %d %d %d", + conn->total_bytes_xmit, + conn->num_xoff_recv, + conn->num_xon_recv); + conn->total_bytes_xmit /= 2; + conn->num_xoff_recv /= 2; + conn->num_xon_recv /= 2; + } + + conn->num_xoff_recv++; + + /* Client-side check to make sure that XOFF is not sent too early, + * for dropmark attacks. The main sidechannel risk is early cells, + * but we also check to make sure that we have not received more XOFFs + * than could have been generated by the bytes we sent. + */ + if (TO_CONN(conn)->type == CONN_TYPE_AP || conn->hs_ident != NULL) { + uint32_t limit = 0; + + /* TODO: This limit technically needs to come from negotiation, + * and be bounds checked for sanity, because the other endpoint + * may have a different consensus */ + if (conn->hs_ident) + limit = xoff_client; + else + limit = xoff_exit; + + if (conn->total_bytes_xmit < limit*conn->num_xoff_recv) { + log_fn(LOG_PROTOCOL_WARN, LD_EDGE, + "Got extra XOFF for bytes sent. Got %d, expected max %d", + conn->num_xoff_recv, conn->total_bytes_xmit/limit); + /* We still process this, because the only dropmark defenses + * in C tor are via the vanguards addon's use of the read valid + * cells. So just signal that we think this is not valid protocol + * data and proceed. */ + retval = false; + } + } + + // TODO: Count how many xoffs we have; log if "too many", for shadow + // analysis of chatter. Possibly add to extra-info? + + log_info(LD_EDGE, "Got XOFF!"); + connection_stop_reading(TO_CONN(conn)); + conn->xoff_received = true; + + return retval; +} + +/** + * Process a stream XON, and if it validates, clear the xoff + * flag and resume reading on this edge connection. + * + * Also, use provided rate information to rate limit + * reading on this edge (or packagaing from it onto + * the circuit), to avoid XON/XOFF chatter. + * + * Returns true if the XON validates, false otherwise. + */ +bool +circuit_process_stream_xon(edge_connection_t *conn, + const crypt_path_t *layer_hint, + const cell_t *cell) +{ + xon_cell_t *xon; + bool retval = true; + + if (BUG(!conn)) { + log_fn(LOG_PROTOCOL_WARN, LD_EDGE, + "Got XON on invalid stream?"); + return false; + } + + /* Make sure this XON came from the right hop */ + if (layer_hint && layer_hint != conn->cpath_layer) { + log_fn(LOG_PROTOCOL_WARN, LD_EDGE, + "Got XON from wrong hop."); + return false; + } + + if (edge_get_ccontrol(conn) == NULL) { + log_fn(LOG_PROTOCOL_WARN, LD_EDGE, + "Got XON for non-congestion control circuit"); + return false; + } + + if (xon_cell_parse(&xon, cell->payload+RELAY_HEADER_SIZE, + CELL_PAYLOAD_SIZE-RELAY_HEADER_SIZE) < 0) { + log_fn(LOG_PROTOCOL_WARN, LD_EDGE, + "Received malformed XON cell."); + return false; + } + + /* If we are near the max, scale everything down */ + if (conn->num_xon_recv == XON_COUNT_SCALE_AT) { + log_info(LD_EDGE, "Scaling down for XON count: %d %d %d", + conn->total_bytes_xmit, + conn->num_xoff_recv, + conn->num_xon_recv); + conn->total_bytes_xmit /= 2; + conn->num_xoff_recv /= 2; + conn->num_xon_recv /= 2; + } + + conn->num_xon_recv++; + + /* Client-side check to make sure that XON is not sent too early, + * for dropmark attacks. The main sidechannel risk is early cells, + * but we also check to see that we did not get more XONs than make + * sense for the number of bytes we sent. + */ + if (TO_CONN(conn)->type == CONN_TYPE_AP || conn->hs_ident != NULL) { + uint32_t limit = 0; + + /* TODO: This limit technically needs to come from negotiation, + * and be bounds checked for sanity, because the other endpoint + * may have a different consensus */ + if (conn->hs_ident) + limit = MIN(xoff_client, xon_rate_bytes); + else + limit = MIN(xoff_exit, xon_rate_bytes); + + if (conn->total_bytes_xmit < limit*conn->num_xon_recv) { + log_fn(LOG_PROTOCOL_WARN, LD_EDGE, + "Got extra XON for bytes sent. Got %d, expected max %d", + conn->num_xon_recv, conn->total_bytes_xmit/limit); + + /* We still process this, because the only dropmark defenses + * in C tor are via the vanguards addon's use of the read valid + * cells. So just signal that we think this is not valid protocol + * data and proceed. */ + retval = false; + } + } + + log_info(LD_EDGE, "Got XON: %d", xon->kbps_ewma); + + /* Adjust the token bucket of this edge connection with the drain rate in + * the XON. Rate is in bytes from kilobit (kpbs). */ + uint64_t rate = ((uint64_t) xon_cell_get_kbps_ewma(xon) * 1000); + if (rate == 0 || INT32_MAX < rate) { + /* No rate. */ + rate = INT32_MAX; + } + token_bucket_rw_adjust(&conn->bucket, (uint32_t) rate, (uint32_t) rate); + + if (conn->xoff_received) { + /* Clear the fact that we got an XOFF, so that this edge can + * start and stop reading normally */ + conn->xoff_received = false; + connection_start_reading(TO_CONN(conn)); + } + + xon_cell_free(xon); + + return retval; +} + +/** + * Called from sendme_stream_data_received(), when data arrives + * from a circuit to our edge's outbuf, to decide if we need to send + * an XOFF. + * + * Returns the amount of cells remaining until the buffer is full, at + * which point it sends an XOFF, and returns 0. + * + * Returns less than 0 if we have queued more than a congestion window + * worth of data and need to close the circuit. + */ +int +flow_control_decide_xoff(edge_connection_t *stream) +{ + size_t total_buffered = connection_get_outbuf_len(TO_CONN(stream)); + uint32_t buffer_limit_xoff = 0; + + if (BUG(edge_get_ccontrol(stream) == NULL)) { + log_err(LD_BUG, "Flow control called for non-congestion control circuit"); + return -1; + } + + /* Onion services and clients are typically localhost edges, so they + * need different buffering limits than exits do */ + if (TO_CONN(stream)->type == CONN_TYPE_AP || stream->hs_ident != NULL) { + buffer_limit_xoff = xoff_client; + } else { + buffer_limit_xoff = xoff_exit; + } + + if (total_buffered > buffer_limit_xoff) { + if (!stream->xoff_sent) { + log_info(LD_EDGE, "Sending XOFF: %"TOR_PRIuSZ" %d", + total_buffered, buffer_limit_xoff); + tor_trace(TR_SUBSYS(cc), TR_EV(flow_decide_xoff_sending), stream); + + circuit_send_stream_xoff(stream); + + /* Clear the drain rate. It is considered wrong if we + * got all the way to XOFF */ + stream->ewma_drain_rate = 0; + } + } + + /* If the outbuf has accumulated more than the expected burst limit of + * cells, then assume it is not draining, and call decide_xon. We must + * do this because writes only happen when the socket unblocks, so + * may not otherwise notice accumulation of data in the outbuf for + * advisory XONs. */ + if (total_buffered > MAX_EXPECTED_CELL_BURST*RELAY_PAYLOAD_SIZE) { + flow_control_decide_xon(stream, 0); + } + + /* Flow control always takes more data; we rely on the oomkiller to + * handle misbehavior. */ + return 0; +} + +/** + * Returns true if the stream's drain rate has changed significantly. + * + * Returns false if the monotime clock is stalled, or if we have + * no previous drain rate information. + */ +static bool +stream_drain_rate_changed(const edge_connection_t *stream) +{ + if (!is_monotime_clock_reliable()) { + return false; + } + + if (!stream->ewma_rate_last_sent) { + return false; + } + + if (stream->ewma_drain_rate > + (100+(uint64_t)xon_change_pct)*stream->ewma_rate_last_sent/100) { + return true; + } + + if (stream->ewma_drain_rate < + (100-(uint64_t)xon_change_pct)*stream->ewma_rate_last_sent/100) { + return true; + } + + return false; +} + +/** + * Called whenever we drain an edge connection outbuf by writing on + * its socket, to decide if it is time to send an xon. + * + * The n_written parameter tells us how many bytes we have written + * this time, which is used to compute the advisory drain rate fields. + */ +void +flow_control_decide_xon(edge_connection_t *stream, size_t n_written) +{ + size_t total_buffered = connection_get_outbuf_len(TO_CONN(stream)); + + /* Bounds check the number of drained bytes, and scale */ + if (stream->drained_bytes >= UINT32_MAX - n_written) { + /* Cut the bytes in half, and move the start time up halfway to now + * (if we have one). */ + stream->drained_bytes /= 2; + + if (stream->drain_start_usec) { + uint64_t now = monotime_absolute_usec(); + + stream->drain_start_usec = now - (now-stream->drain_start_usec)/2; + } + } + + /* Accumulate drained bytes since last rate computation */ + stream->drained_bytes += n_written; + + tor_trace(TR_SUBSYS(cc), TR_EV(flow_decide_xon), stream, n_written); + + /* Check for bad monotime clock and bytecount wrap */ + if (!is_monotime_clock_reliable()) { + /* If the monotime clock ever goes wrong, the safest thing to do + * is just clear our short-term rate info and wait for the clock to + * become reliable again.. */ + stream->drain_start_usec = 0; + stream->drained_bytes = 0; + } else { + /* If we have no drain start timestamp, and we still have + * remaining buffer, start the buffering counter */ + if (!stream->drain_start_usec && total_buffered > 0) { + log_debug(LD_EDGE, "Began edge buffering: %d %d %"TOR_PRIuSZ, + stream->ewma_rate_last_sent, + stream->ewma_drain_rate, + total_buffered); + tor_trace(TR_SUBSYS(cc), TR_EV(flow_decide_xon_drain_start), + stream); + stream->drain_start_usec = monotime_absolute_usec(); + stream->drained_bytes = 0; + } + } + + if (stream->drain_start_usec) { + /* If we have spent enough time in a queued state, update our drain + * rate. */ + if (stream->drained_bytes > xon_rate_bytes) { + /* No previous drained bytes means it is the first time we are computing + * it so use the value we just drained onto the socket as a baseline. It + * won't be accurate but it will be a start towards the right value. + * + * We have to do this in order to have a drain rate else we could be + * sending a drain rate of 0 in an XON which would be undesirable and + * basically like sending an XOFF. */ + if (stream->prev_drained_bytes == 0) { + stream->prev_drained_bytes = stream->drained_bytes; + } + uint32_t drain_rate = compute_drain_rate(stream); + /* Once the drain rate has been computed, note how many bytes we just + * drained so it can be used at the next calculation. We do this here + * because it gets reset once the rate is changed. */ + stream->prev_drained_bytes = stream->drained_bytes; + + if (drain_rate) { + stream->ewma_drain_rate = + (uint32_t)n_count_ewma(drain_rate, + stream->ewma_drain_rate, + xon_ewma_cnt); + log_debug(LD_EDGE, "Updating drain rate: %d %d %"TOR_PRIuSZ, + drain_rate, + stream->ewma_drain_rate, + total_buffered); + tor_trace(TR_SUBSYS(cc), TR_EV(flow_decide_xon_drain_update), + stream, drain_rate); + /* Reset recent byte counts. This prevents us from sending advisory + * XONs more frequent than every xon_rate_bytes. */ + stream->drained_bytes = 0; + stream->drain_start_usec = 0; + } + } + } + + /* If we don't have an XOFF outstanding, consider updating an + * old rate */ + if (!stream->xoff_sent) { + if (stream_drain_rate_changed(stream)) { + /* If we are still buffering and the rate changed, update + * advisory XON */ + log_info(LD_EDGE, "Sending rate-change XON: %d %d %"TOR_PRIuSZ, + stream->ewma_rate_last_sent, + stream->ewma_drain_rate, + total_buffered); + tor_trace(TR_SUBSYS(cc), TR_EV(flow_decide_xon_rate_change), stream); + circuit_send_stream_xon(stream); + } + } else if (total_buffered == 0) { + log_info(LD_EDGE, "Sending XON: %d %d %"TOR_PRIuSZ, + stream->ewma_rate_last_sent, + stream->ewma_drain_rate, + total_buffered); + tor_trace(TR_SUBSYS(cc), TR_EV(flow_decide_xon_partial_drain), stream); + circuit_send_stream_xon(stream); + } + + /* If the buffer has fully emptied, clear the drain timestamp, + * so we can total only bytes drained while outbuf is 0. */ + if (total_buffered == 0) { + stream->drain_start_usec = 0; + + /* After we've spent 'xon_rate_bytes' with the queue fully drained, + * double any rate we sent. */ + if (stream->drained_bytes >= xon_rate_bytes && + stream->ewma_rate_last_sent) { + stream->ewma_drain_rate = MIN(INT32_MAX, 2*stream->ewma_drain_rate); + + log_debug(LD_EDGE, + "Queue empty for xon_rate_limit bytes: %d %d", + stream->ewma_rate_last_sent, + stream->ewma_drain_rate); + tor_trace(TR_SUBSYS(cc), TR_EV(flow_decide_xon_drain_doubled), stream); + /* Resetting the drained bytes count. We need to keep its value as a + * previous so the drain rate calculation takes into account what was + * actually drain the last time. */ + stream->prev_drained_bytes = stream->drained_bytes; + stream->drained_bytes = 0; + } + } + + return; +} + +/** + * Note that we packaged some data on this stream. Used to enforce + * client-side dropmark limits + */ +void +flow_control_note_sent_data(edge_connection_t *stream, size_t len) +{ + /* If we are near the max, scale everything down */ + if (stream->total_bytes_xmit >= TOTAL_XMIT_SCALE_AT-len) { + log_info(LD_EDGE, "Scaling down for flow control xmit bytes:: %d %d %d", + stream->total_bytes_xmit, + stream->num_xoff_recv, + stream->num_xon_recv); + + stream->total_bytes_xmit /= 2; + stream->num_xoff_recv /= 2; + stream->num_xon_recv /= 2; + } + + stream->total_bytes_xmit += len; +} + +/** Returns true if an edge connection uses flow control */ +bool +edge_uses_flow_control(const edge_connection_t *stream) +{ + bool ret = (stream->on_circuit && stream->on_circuit->ccontrol) || + (stream->cpath_layer && stream->cpath_layer->ccontrol); + + /* All circuits with congestion control use flow control */ + return ret; +} + +/** + * Returns the max RTT for the circuit that carries this stream, + * as observed by congestion control. + */ +uint64_t +edge_get_max_rtt(const edge_connection_t *stream) +{ + if (stream->on_circuit && stream->on_circuit->ccontrol) + return stream->on_circuit->ccontrol->max_rtt_usec; + else if (stream->cpath_layer && stream->cpath_layer->ccontrol) + return stream->cpath_layer->ccontrol->max_rtt_usec; + + return 0; +} + +/** Returns true if a connection is an edge conn that uses flow control */ +bool +conn_uses_flow_control(connection_t *conn) +{ + bool ret = false; + + if (CONN_IS_EDGE(conn)) { + edge_connection_t *edge = TO_EDGE_CONN(conn); + + if (edge_uses_flow_control(edge)) { + ret = true; + } + } + + return ret; +} + |