cc: initial implementation of BBRv2 congestion control algorithm

Based on draft-cardwell-iccrg-bbr-congestion-control-02.

Largely based on bbr module but most of functions are
renamed/changed a bit. per_loss.rs contains loss-related
functions.

quiche/include/quiche.h

@@ -219,6 +219,7 @@ enum quiche_cc_algorithm {
     QUICHE_CC_RENO = 0,
     QUICHE_CC_CUBIC = 1,
     QUICHE_CC_BBR = 2,
+    QUICHE_CC_BBR2 = 3,
 };
 
 // Sets the congestion control algorithm used.

quiche/src/recovery/bbr2/init.rs

@@ -0,0 +1,90 @@
+// Copyright (C) 2022, Cloudflare, Inc.
+// All rights reserved.
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright notice,
+//       this list of conditions and the following disclaimer.
+//
+//     * Redistributions in binary form must reproduce the above copyright
+//       notice, this list of conditions and the following disclaimer in the
+//       documentation and/or other materials provided with the distribution.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS
+// IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
+// THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
+// PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR
+// CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
+// EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
+// PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
+// PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
+// LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
+// NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
+// SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+use super::*;
+use crate::recovery::Recovery;
+
+use std::time::Instant;
+
+// BBR2 Functions at Initialization.
+//
+
+// 4.2.1.  Initialization
+pub fn bbr2_init(r: &mut Recovery) {
+    let rtt = r.rtt();
+    let now = Instant::now();
+
+    let bbr = &mut r.bbr2_state;
+    bbr.min_rtt = rtt;
+    bbr.min_rtt_stamp = now;
+    bbr.probe_rtt_done_stamp = None;
+    bbr.probe_rtt_round_done = false;
+    bbr.prior_cwnd = 0;
+    bbr.idle_restart = false;
+    bbr.extra_acked_interval_start = now;
+    bbr.extra_acked_delivered = 0;
+    bbr.bw_lo = u64::MAX;
+    bbr.bw_hi = u64::MAX;
+    bbr.inflight_lo = usize::MAX;
+    bbr.inflight_hi = usize::MAX;
+    bbr.probe_up_cnt = usize::MAX;
+
+    r.send_quantum = r.max_datagram_size;
+
+    per_loss::bbr2_reset_congestion_signals(r);
+    per_loss::bbr2_reset_lower_bounds(r);
+    bbr2_init_round_counting(r);
+    bbr2_init_full_pipe(r);
+    pacing::bbr2_init_pacing_rate(r);
+    bbr2_enter_startup(r);
+}
+
+// 4.5.1.  BBR.round_count: Tracking Packet-Timed Round Trips
+fn bbr2_init_round_counting(r: &mut Recovery) {
+    let bbr = &mut r.bbr2_state;
+
+    bbr.next_round_delivered = 0;
+    bbr.round_start = false;
+    bbr.round_count = 0;
+}
+
+// 4.3.1.1.  Startup Dynamics
+pub fn bbr2_enter_startup(r: &mut Recovery) {
+    let bbr = &mut r.bbr2_state;
+
+    bbr.state = BBR2StateMachine::Startup;
+    bbr.pacing_gain = STARTUP_PACING_GAIN;
+    bbr.cwnd_gain = STARTUP_CWND_GAIN;
+}
+
+// 4.3.1.2.  Exiting Startup Based on Bandwidth Plateau
+fn bbr2_init_full_pipe(r: &mut Recovery) {
+    let bbr = &mut r.bbr2_state;
+
+    bbr.filled_pipe = false;
+    bbr.full_bw = 0;
+    bbr.full_bw_count = 0;
+}