35.2. 准备 RHEL 启用 MPTCP 支持

流程

1. 在内核中启用 MPTCP 套接字：

   # echo "net.mptcp.enabled=1" > /etc/sysctl.d/90-enable-MPTCP.conf
   # sysctl -p /etc/sysctl.d/90-enable-MPTCP.conf

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2. 验证内核中是否启用了 MPTCP：

   # sysctl -a | grep mptcp.enabled
   net.mptcp.enabled = 1

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3. 使用以下内容创建 mptcp-app.stap 文件：

   #!/usr/bin/env stap
   
   %{
   #include <linux/in.h>
   #include <linux/ip.h>
   %}
   
   /* RSI contains 'type' and RDX contains 'protocol'.
    */
   
   function mptcpify () %{
       if (CONTEXT->kregs->si == SOCK_STREAM &&
           (CONTEXT->kregs->dx == IPPROTO_TCP ||
            CONTEXT->kregs->dx == 0)) {
                   CONTEXT->kregs->dx = IPPROTO_MPTCP;
                   STAP_RETVALUE = 1;
       } else {
              STAP_RETVALUE = 0;
       }
   %}
   
   probe kernel.function("__sys_socket") {
           if (mptcpify() == 1) {
                   printf("command %16s mptcpified\n", execname());
           }
   }

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4. 强制用户空间应用程序创建 MPTCP 套接字而不是 TCP 套接字：

   # stap -vg mptcp-app.stap

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   注意：此操作会影响命令之后启动的所有 TCP 套接字。在使用 Ctrl+C 中断上述命令后，应用将继续使用 TCP 套接字。

5. 另外，要允许 MPTCP 只用于特定的应用程序，您可以使用以下内容修改 mptcp-app.stap 文件：

   #!/usr/bin/env stap
   
   %{
   #include <linux/in.h>
   #include <linux/ip.h>
   %}
   
   /* according to [1], RSI contains 'type' and RDX
    * contains 'protocol'.
    * [1] https://github.com/torvalds/linux/blob/master/arch/x86/entry/entry_64.S#L79
    */
   
   function mptcpify () %{
   	if (CONTEXT->kregs->si == SOCK_STREAM &&
   	    (CONTEXT->kregs->dx == IPPROTO_TCP ||
   	     CONTEXT->kregs->dx == 0)) {
   		CONTEXT->kregs->dx = IPPROTO_MPTCP;
   		STAP_RETVALUE = 1;
   	} else {
   		STAP_RETVALUE = 0;
   	}
   %}
   
   probe kernel.function("__sys_socket") {
   	cur_proc = execname()
   	if ((cur_proc == @1) && (mptcpify() == 1)) {
   		printf("command %16s mptcpified\n", cur_proc);
   	}
   }

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6. 在可选择的情况下，假设您想要强制 iperf3 工具使用 MPTCP 而不是 TCP。要做到这一点，请输入以下命令：

   # stap -vg mptcp-app.stap iperf3

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7. 在 mptcp-app.stap 脚本安装内核探测后，会在内核 dmesg 输出中出现以下警告

   # dmesg
   ...
   [ 1752.694072] Kprobes globally unoptimized
   [ 1752.730147] stap_1ade3b3356f3e68765322e26dec00c3d_1476: module_layout: kernel tainted.
   [ 1752.732162] Disabling lock debugging due to kernel taint
   [ 1752.733468] stap_1ade3b3356f3e68765322e26dec00c3d_1476: loading out-of-tree module taints kernel.
   [ 1752.737219] stap_1ade3b3356f3e68765322e26dec00c3d_1476: module verification failed: signature and/or required key missing - tainting kernel
   [ 1752.737219] stap_1ade3b3356f3e68765322e26dec00c3d_1476 (mptcp-app.stap): systemtap: 4.5/0.185, base: ffffffffc0550000, memory: 224data/32text/57ctx/65638net/367alloc kb, probes: 1

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8. 启动 iperf3 服务器：

   # iperf3 -s
   
   Server listening on 5201

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9. 将客户端连接到服务器：

   # iperf3 -c 127.0.0.1 -t 3

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10. 建立连接后，验证 ss 输出以查看特定于子流的状态：

    # ss -nti '( dport :5201 )'
    
    State Recv-Q Send-Q Local Address:Port Peer Address:Port Process
    ESTAB 0      0      127.0.0.1:41842    127.0.0.1:5201
    cubic wscale:7,7 rto:205 rtt:4.455/8.878 ato:40 mss:21888 pmtu:65535 rcvmss:536 advmss:65483 cwnd:10 bytes_sent:141 bytes_acked:142 bytes_received:4 segs_out:8 segs_in:7 data_segs_out:3 data_segs_in:3 send 393050505bps lastsnd:2813 lastrcv:2772 lastack:2772 pacing_rate 785946640bps delivery_rate 10944000000bps delivered:4 busy:41ms rcv_space:43690 rcv_ssthresh:43690 minrtt:0.008 tcp-ulp-mptcp flags:Mmec token:0000(id:0)/2ff053ec(id:0) seq:3e2cbea12d7673d4 sfseq:3 ssnoff:ad3d00f4 maplen:2

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11. 验证 MPTCP 计数器：

    # nstat MPTcp*
    
    #kernel
    MPTcpExtMPCapableSYNRX          2                  0.0
    MPTcpExtMPCapableSYNTX          2                  0.0
    MPTcpExtMPCapableSYNACKRX       2                  0.0
    MPTcpExtMPCapableACKRX          2                  0.0

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