bbr/0002-ip-introduce-the-ecn_low-per-route-feature.patch at d257091c3d09d36524e7ed83f74106f4c9e505a5 · google/bbr · GitHub

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From 537b1b761e1d0036923adba7a80d3655cfff095d Mon Sep 17 00:00:00 2001
From: David Morley <morleyd@google.com>
Date: Fri, 21 Jul 2023 09:20:46 +0000
Subject: [PATCH 1/2] ip: introduce the ecn_low per-route feature

Add a a new "ecn_low" feature that administrators can add to a
particular ip route. The ecn_low feature indicates that the given
destination network is a low-latency ECN environment, meaning both
that ECN CE marks are applied by the network using a low-latency
marking threshold and also that TCP endpoints provide precise
per-data-segment ECN feedback in ACKs (where the ACK ECE flag echoes
the received CE status of all newly-acknowledged data segments). This
ecn_low feature indication can be used by congestion control
algorithms to decide how to interpret ECN signals over the given
destination network.

Signed-off-by: David Morley <morleyd@google.com>
Signed-off-by: Neal Cardwell <ncardwell@google.com>
---
 include/uapi/linux/rtnetlink.h |  4 +++-
 ip/iproute.c                   |  8 +++++++-
 man/man8/ip-route.8.in         | 19 ++++++++++++++-----
 3 files changed, 24 insertions(+), 7 deletions(-)

diff --git a/include/uapi/linux/rtnetlink.h b/include/uapi/linux/rtnetlink.h
index 2132e941b93a..66e3237ea915 100644
--- a/include/uapi/linux/rtnetlink.h
+++ b/include/uapi/linux/rtnetlink.h
@@ -506,9 +506,11 @@ enum {
 #define RTAX_FEATURE_SACK	(1 << 1)
 #define RTAX_FEATURE_TIMESTAMP	(1 << 2)
 #define RTAX_FEATURE_ALLFRAG	(1 << 3)
+#define RTAX_FEATURE_ECN_LOW	(1 << 4)

 #define RTAX_FEATURE_MASK	(RTAX_FEATURE_ECN | RTAX_FEATURE_SACK | \
-				 RTAX_FEATURE_TIMESTAMP | RTAX_FEATURE_ALLFRAG)
+				 RTAX_FEATURE_TIMESTAMP | RTAX_FEATURE_ALLFRAG | \
+				 RTAX_FEATURE_ECN_LOW)

 struct rta_session {
 	__u8	proto;
diff --git a/ip/iproute.c b/ip/iproute.c
index fdf1f9a9dd0a..bd5d783cfdbb 100644
--- a/ip/iproute.c
+++ b/ip/iproute.c
@@ -96,7 +96,7 @@ static void usage(void)
 		"PREF := [ low | medium | high ]\n"
 		"TIME := NUMBER[s|ms]\n"
 		"BOOL := [1|0]\n"
-		"FEATURES := ecn\n"
+		"FEATURES := [ ecn | ecn_low ]\n"
 		"ENCAPTYPE := [ mpls | ip | ip6 | seg6 | seg6local | rpl | ioam6 | xfrm ]\n"
 		"ENCAPHDR := [ MPLSLABEL | SEG6HDR | SEG6LOCAL | IOAM6HDR | XFRMINFO ]\n"
 		"SEG6HDR := [ mode SEGMODE ] segs ADDR1,ADDRi,ADDRn [hmac HMACKEYID] [cleanup]\n"
@@ -350,6 +350,10 @@ static void print_rtax_features(FILE *fp, unsigned int features)
 		print_null(PRINT_ANY, "ecn", "ecn ", NULL);
 		features &= ~RTAX_FEATURE_ECN;
 	}
+	if (features & RTAX_FEATURE_ECN_LOW) {
+		print_null(PRINT_ANY, "ecn_low", "ecn_low ", NULL);
+		features &= ~RTAX_FEATURE_ECN_LOW;
+	}

 	if (features)
 		print_0xhex(PRINT_ANY,
@@ -1349,6 +1353,8 @@ static int iproute_modify(int cmd, unsigned int flags, int argc, char **argv)

 				if (strcmp(*argv, "ecn") == 0)
 					features |= RTAX_FEATURE_ECN;
+				else if (strcmp(*argv, "ecn_low") == 0)
+					features |= RTAX_FEATURE_ECN_LOW;
 				else
 					invarg("\"features\" value not valid\n", *argv);
 				break;
diff --git a/man/man8/ip-route.8.in b/man/man8/ip-route.8.in
index c2b00833e507..10f35f38e6a2 100644
--- a/man/man8/ip-route.8.in
+++ b/man/man8/ip-route.8.in
@@ -181,7 +181,7 @@ throw " | " unreachable " | " prohibit " | " blackhole " | " nat " ]"

 .ti -8
 .IR FEATURES " := [ "
-.BR ecn " | ]"
+.BR ecn " | " ecn_low " ] "

 .ti -8
 .IR PREF " := [ "
@@ -544,16 +544,25 @@ The default value is zero, meaning to use Slow Start value.

 .TP
 .BI features " FEATURES " (Linux 3.18+ only)
-Enable or disable per-route features. Only available feature at this
-time is
-.B ecn
-to enable explicit congestion notification when initiating connections to the
+Enable or disable per-route features. Available features include:
+
+.BI ecn
+- to enable explicit congestion notification when initiating connections to the
 given destination network.
 When responding to a connection request from the given network, ecn will
 also be used even if the
 .B net.ipv4.tcp_ecn
 sysctl is set to 0.

+.BI ecn_low
+- to indicate that the given destination network is a low-latency ECN
+environment, meaning both that ECN CE marks are applied by the network using a
+low-latency marking threshold and also that TCP endpoints provide precise
+per-data-segment ECN feedback in ACKs (where the ACK ECE flag echoes the
+received CE status of all newly-acknowledged data segments). This ecn_low
+feature indication can be used by congestion control algorithms to decide how
+to interpret ECN signals over the given destination network (Linux 6.7+ only).
+
 .TP
 .BI quickack " BOOL " "(Linux 3.11+ only)"
 Enable or disable quick ack for connections to this destination.
--
2.41.0.487.g6d72f3e995-goog