BCC: python: add a useful tool for mptcp

Multipath TCP (MPTCP) is an extension of the standard TCP protocol
that allows a single transport connection to use multiple network
interfaces or paths. MPTCP is useful for applications like bandwidth
aggregation, failover, and more resilient connections.

Linux kernel starts to support MPTCP since v5.6, this patch provides
a method which can easily force applications use MPTCP socket without
modifing its code.

Co-developed-by: Geliang Tang <[email protected]>
Signed-off-by: Geliang Tang <[email protected]>
Signed-off-by: Gang Yan <[email protected]>

Author: Dwyane-Yan

README.md

@@ -173,6 +173,7 @@ pair of .c and .py files, and some are directories of files.
 - tools/[tcptop](tools/tcptop.py): Summarize TCP send/recv throughput by host. Top for TCP. [Examples](tools/tcptop_example.txt).
 - tools/[tcptracer](tools/tcptracer.py): Trace TCP established connections (connect(), accept(), close()). [Examples](tools/tcptracer_example.txt).
 - tools/[tcpcong](tools/tcpcong.py): Trace TCP socket congestion control status duration. [Examples](tools/tcpcong_example.txt).
+- tools/[mptcpify](tools/mptcpify.py): Force applications to use MPTCP instead of TCP. [Examples](tools/mptcpify_example.txt).
 
 ##### Storage and Filesystems Tools
 

tools/mptcpify.py

@@ -0,0 +1,92 @@
+#!/usr/bin/env python
+#
+# mptcpify Make the applications to use MPTCP.
+#           For Linux, uses BCC, eBPF. Embedded C.
+#
+# USAGE: ./mptcpify
+#        ./mptcpify -t curl,iperf3
+#
+# Copyright 2025 Kylin Software, Inc.
+# Licensed under the Apache License, Version 2.0 (the "License")
+#
+# 05-Apr-2025   Gang Yan   Created this.
+
+import ctypes as ct
+import argparse
+import signal
+import time
+
+from bcc import BPF
+
+#arguments
+parser = argparse.ArgumentParser(
+         description="mptcpify try to force applications to use MPTCP instead of TCP")
+parser.add_argument("-t", "--targets", type=str,
+                    help="use ',' for multi targets, eg: 'iperf3,rsync'. "
+                         "Without '-t', it can works on all applications by default.")
+
+args_str = parser.parse_args()
+if args_str.targets != None:
+    mode = 1
+    args_list = [t.strip() for t in args_str.targets.split(',')]
+else:
+    mode = 0
+
+if (not BPF.support_fmod_ret()):
+    print("Your kernel version is too old,"
+          " fmod_ret method is only support kernel v5.7 and later.")
+    exit()
+
+TASK_COMM_LEN = 16
+
+class app_name(ct.Structure):
+    _fields_ = [("str", ct.c_char * TASK_COMM_LEN)]
+
+# define BPF program
+prog = """
+#include <linux/net.h>
+#include <uapi/linux/in.h>
+#include <linux/string.h>
+
+struct app_name {
+    char name[TASK_COMM_LEN];
+};
+
+BPF_ARRAY(work_mode, int, 1);
+BPF_HASH(support_apps, struct app_name);
+
+KMOD_RET(update_socket_protocol, int family, int type, int protocol, int ret)
+{
+    struct app_name target = {};
+    int index = 0;
+    int *mode = work_mode.lookup(&index);
+    bpf_get_current_comm(&target.name, TASK_COMM_LEN);
+
+    if ((family == AF_INET || family == AF_INET6) &&
+        type == SOCK_STREAM &&
+        (!protocol || protocol == IPPROTO_TCP) &&
+        (*mode == 0 || support_apps.lookup(&target)))
+        return IPPROTO_MPTCP;
+
+    return protocol;
+
+}
+
+"""
+
+b = BPF(text=prog)
+b.attach_fmod_ret("update_socket_protocol")
+
+work_mode = b["work_mode"]
+support_apps = b.get_table("support_apps")
+if mode:
+    for i in args_list:
+        app = i.encode()
+        name = app_name()
+        name.str = app[:TASK_COMM_LEN-1].ljust(TASK_COMM_LEN, b'\0')
+        support_apps[name] = ct.c_uint32(1)
+
+work_mode[ct.c_int(0)] = ct.c_int(mode)
+
+print("MPTCP is been forced for ", args_list if mode == 1 else "all applications");
+signal.pause()

tools/mptcpify_example.txt

@@ -0,0 +1,44 @@
+Demonstrations of mptcpify, the Linux eBPF/bcc version.
+
+
+mptcpify forces the application to use to MPTCP instead of TCP.
+
+mptcpify has been verified with iperf3 and rsync[TCP module]. It can be used
+for incresing the speed of transferring data with rsync.
+
+The MPTCP configuration is decribed in
+https://www.mptcp.dev/pm.html
+
+USAGE message:
+
+usage: sudo python ./mptcpify.py [-h] [-t TARGETS]
+
+mptcpify try to force applications to use MPTCP instead of TCP
+
+options:
+  -h, --help            show this help message and exit
+  -t TARGETS, --targets TARGETS
+                        use ',' for multi targets, eg: 'iperf3,rsync'. Without '-t', it can works on all applications by default.
+
+Here are some example output.
+
+1、curl
+	$ curl https://check.mptcp.dev
+	You are not using MPTCP.
+
+	$ sudo python3 mptcpify.py -t curl &
+	$ curl https://check.mptcp.dev
+	You are using MPTCP.
+
+2、iperf3
+	'iperf.sh' can be obtained through th link below:
+	https://github.com/Dwyane-Yan/bcc_test_iperf/blob/main/iperf.sh
+
+	$ sudo ./iperf.sh
+	[ ID] Interval Transfer Bitrate
+	[ 5] 0.00-1.00 sec 11.4 MBytes 95.3 Mbits/sec
+
+	$ sudo python3 mptcpify.py -t iperf3
+	$ sudo ./iperf.sh
+	[ ID] Interval Transfer Bitrate
+	[ 5] 0.00-1.00 sec 87.0 MBytes 729 Mbits/sec