File net-sched-act_skbmod-Add-SKBMOD_F_ECN-option-support.patch of Package linux-glibc-devel.26130
From 56af5e749f20c3a540310c207dcc373f4f09156e Mon Sep 17 00:00:00 2001
From: Peilin Ye <peilin.ye@bytedance.com>
Date: Tue, 27 Jul 2021 18:33:15 -0700
Subject: [PATCH] net/sched: act_skbmod: Add SKBMOD_F_ECN option support
Git-commit: 56af5e749f20c3a540310c207dcc373f4f09156e
Patch-mainline: v5.15-rc1
References: bsc#1189998
Currently, when doing rate limiting using the tc-police(8) action, the
easiest way is to simply drop the packets which exceed or conform the
configured bandwidth limit. Add a new option to tc-skbmod(8), so that
users may use the ECN [1] extension to explicitly inform the receiver
about the congestion instead of dropping packets "on the floor".
The 2 least significant bits of the Traffic Class field in IPv4 and IPv6
headers are used to represent different ECN states [2]:
0b00: "Non ECN-Capable Transport", Non-ECT
0b10: "ECN Capable Transport", ECT(0)
0b01: "ECN Capable Transport", ECT(1)
0b11: "Congestion Encountered", CE
As an example:
$ tc filter add dev eth0 parent 1: protocol ip prio 10 \
matchall action skbmod ecn
Doing the above marks all ECT(0) and ECT(1) packets as CE. It does NOT
affect Non-ECT or non-IP packets. In the tc-police scenario mentioned
above, users may pipe a tc-police action and a tc-skbmod "ecn" action
together to achieve ECN-based rate limiting.
For TCP connections, upon receiving a CE packet, the receiver will respond
with an ECE packet, asking the sender to reduce their congestion window.
However ECN also works with other L4 protocols e.g. DCCP and SCTP [2], and
our implementation does not touch or care about L4 headers.
The updated tc-skbmod SYNOPSIS looks like the following:
tc ... action skbmod { set SETTABLE | swap SWAPPABLE | ecn } ...
Only one of "set", "swap" or "ecn" shall be used in a single tc-skbmod
command. Trying to use more than one of them at a time is considered
undefined behavior; pipe multiple tc-skbmod commands together instead.
"set" and "swap" only affect Ethernet packets, while "ecn" only affects
IPv{4,6} packets.
It is also worth mentioning that, in theory, the same effect could be
achieved by piping a "police" action and a "bpf" action using the
bpf_skb_ecn_set_ce() helper, but this requires eBPF programming from the
user, thus impractical.
Depends on patch "net/sched: act_skbmod: Skip non-Ethernet packets".
[1] https://datatracker.ietf.org/doc/html/rfc3168
[2] https://en.wikipedia.org/wiki/Explicit_Congestion_Notification
Reviewed-by: Cong Wang <cong.wang@bytedance.com>
Signed-off-by: Peilin Ye <peilin.ye@bytedance.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Davidlohr Bueso <dbueso@suse.de>
---
include/uapi/linux/tc_act/tc_skbmod.h | 1 +
net/sched/act_skbmod.c | 44 +++++++++++++++++++--------
2 files changed, 33 insertions(+), 12 deletions(-)
diff --git a/include/uapi/linux/tc_act/tc_skbmod.h b/include/uapi/linux/tc_act/tc_skbmod.h
index c525b3503797..af6ef2cfbf3d 100644
--- a/include/linux/tc_act/tc_skbmod.h
+++ b/include/linux/tc_act/tc_skbmod.h
@@ -17,6 +17,7 @@
#define SKBMOD_F_SMAC 0x2
#define SKBMOD_F_ETYPE 0x4
#define SKBMOD_F_SWAPMAC 0x8
+#define SKBMOD_F_ECN 0x10
struct tc_skbmod {
tc_gen;
