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https://github.com/eunomia-bpf/bpf-developer-tutorial.git
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161 lines
5.7 KiB
Markdown
161 lines
5.7 KiB
Markdown
# eBPF入门实践教程：使用 libbpf-bootstrap 开发程序统计 TCP 连接延时
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```tcpstates``` 是一个追踪当前系统上的TCP套接字的TCP状态的程序，主要通过跟踪内核跟踪点 ```inet_sock_set_state``` 来实现。统计数据通过 ```perf_event```向用户态传输。
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```c
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SEC("tracepoint/sock/inet_sock_set_state")
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int handle_set_state(struct trace_event_raw_inet_sock_set_state *ctx)
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```
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在套接字改变状态处附加一个eBPF跟踪函数。
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```c
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if (ctx->protocol != IPPROTO_TCP)
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return 0;
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if (target_family && target_family != family)
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return 0;
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if (filter_by_sport && !bpf_map_lookup_elem(&sports, &sport))
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return 0;
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if (filter_by_dport && !bpf_map_lookup_elem(&dports, &dport))
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return 0;
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```
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跟踪函数被调用后，先判断当前改变状态的套接字是否满足我们需要的过滤条件，如果不满足则不进行记录。
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```c
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tsp = bpf_map_lookup_elem(×tamps, &sk);
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ts = bpf_ktime_get_ns();
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if (!tsp)
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delta_us = 0;
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else
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delta_us = (ts - *tsp) / 1000;
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event.skaddr = (__u64)sk;
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event.ts_us = ts / 1000;
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event.delta_us = delta_us;
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event.pid = bpf_get_current_pid_tgid() >> 32;
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event.oldstate = ctx->oldstate;
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event.newstate = ctx->newstate;
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event.family = family;
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event.sport = sport;
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event.dport = dport;
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bpf_get_current_comm(&event.task, sizeof(event.task));
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if (family == AF_INET) {
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bpf_probe_read_kernel(&event.saddr, sizeof(event.saddr), &sk->__sk_common.skc_rcv_saddr);
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bpf_probe_read_kernel(&event.daddr, sizeof(event.daddr), &sk->__sk_common.skc_daddr);
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} else { /* family == AF_INET6 */
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bpf_probe_read_kernel(&event.saddr, sizeof(event.saddr), &sk->__sk_common.skc_v6_rcv_saddr.in6_u.u6_addr32);
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bpf_probe_read_kernel(&event.daddr, sizeof(event.daddr), &sk->__sk_common.skc_v6_daddr.in6_u.u6_addr32);
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}
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```
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使用状态改变相关填充event结构体。
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- 此处使用了```libbpf``` 的 CO-RE 支持。
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```c
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bpf_perf_event_output(ctx, &events, BPF_F_CURRENT_CPU, &event, sizeof(event));
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```
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将事件结构体发送至用户态程序。
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```c
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if (ctx->newstate == TCP_CLOSE)
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bpf_map_delete_elem(×tamps, &sk);
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else
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bpf_map_update_elem(×tamps, &sk, &ts, BPF_ANY);
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```
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根据这个TCP链接的新状态，决定是更新下时间戳记录还是不再记录它的时间戳。
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## 用户态程序
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```c
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while (!exiting) {
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err = perf_buffer__poll(pb, PERF_POLL_TIMEOUT_MS);
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if (err < 0 && err != -EINTR) {
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warn("error polling perf buffer: %s\n", strerror(-err));
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goto cleanup;
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}
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/* reset err to return 0 if exiting */
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err = 0;
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}
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```
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不停轮询内核程序所发过来的 ```perf event```。
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```c
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static void handle_event(void* ctx, int cpu, void* data, __u32 data_sz) {
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char ts[32], saddr[26], daddr[26];
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struct event* e = data;
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struct tm* tm;
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int family;
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time_t t;
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if (emit_timestamp) {
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time(&t);
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tm = localtime(&t);
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strftime(ts, sizeof(ts), "%H:%M:%S", tm);
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printf("%8s ", ts);
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}
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inet_ntop(e->family, &e->saddr, saddr, sizeof(saddr));
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inet_ntop(e->family, &e->daddr, daddr, sizeof(daddr));
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if (wide_output) {
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family = e->family == AF_INET ? 4 : 6;
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printf(
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"%-16llx %-7d %-16s %-2d %-26s %-5d %-26s %-5d %-11s -> %-11s "
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"%.3f\n",
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e->skaddr, e->pid, e->task, family, saddr, e->sport, daddr,
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e->dport, tcp_states[e->oldstate], tcp_states[e->newstate],
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(double)e->delta_us / 1000);
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} else {
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printf(
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"%-16llx %-7d %-10.10s %-15s %-5d %-15s %-5d %-11s -> %-11s %.3f\n",
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e->skaddr, e->pid, e->task, saddr, e->sport, daddr, e->dport,
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tcp_states[e->oldstate], tcp_states[e->newstate],
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(double)e->delta_us / 1000);
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}
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}
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static void handle_lost_events(void* ctx, int cpu, __u64 lost_cnt) {
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warn("lost %llu events on CPU #%d\n", lost_cnt, cpu);
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}
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```
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收到事件后所调用对应的处理函数并进行输出打印。
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## 编译运行
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- ```git clone https://github.com/libbpf/libbpf-bootstrap libbpf-bootstrap-cloned```
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- 将 [libbpf-bootstrap](libbpf-bootstrap)目录下的文件复制到 ```libbpf-bootstrap-cloned/examples/c```下
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- 修改 ```libbpf-bootstrap-cloned/examples/c/Makefile``` ，在其 ```APPS``` 项后添加 ```tcpstates```
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- 在 ```libbpf-bootstrap-cloned/examples/c``` 下运行 ```make tcpstates```
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- ```sudo ./tcpstates```
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## 效果
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```plain
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root@yutong-VirtualBox:~/libbpf-bootstrap/examples/c# ./tcpstates
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SKADDR PID COMM LADDR LPORT RADDR RPORT OLDSTATE -> NEWSTATE MS
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ffff9bf61bb62bc0 164978 node 192.168.88.15 0 52.178.17.2 443 CLOSE -> SYN_SENT 0.000
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ffff9bf61bb62bc0 0 swapper/0 192.168.88.15 41596 52.178.17.2 443 SYN_SENT -> ESTABLISHED 225.794
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ffff9bf61bb62bc0 0 swapper/0 192.168.88.15 41596 52.178.17.2 443 ESTABLISHED -> CLOSE_WAIT 901.454
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ffff9bf61bb62bc0 164978 node 192.168.88.15 41596 52.178.17.2 443 CLOSE_WAIT -> LAST_ACK 0.793
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ffff9bf61bb62bc0 164978 node 192.168.88.15 41596 52.178.17.2 443 LAST_ACK -> LAST_ACK 0.086
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ffff9bf61bb62bc0 228759 kworker/u6 192.168.88.15 41596 52.178.17.2 443 LAST_ACK -> CLOSE 0.193
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ffff9bf6d8ee88c0 229832 redis-serv 0.0.0.0 6379 0.0.0.0 0 CLOSE -> LISTEN 0.000
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ffff9bf6d8ee88c0 229832 redis-serv 0.0.0.0 6379 0.0.0.0 0 LISTEN -> CLOSE 1.763
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ffff9bf7109d6900 88750 node 127.0.0.1 39755 127.0.0.1 50966 ESTABLISHED -> FIN_WAIT1 0.000
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```
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对于输出的详细解释，详见 [README.md](README.md)
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## 总结
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这里的代码修改自 <https://github.com/iovisor/bcc/blob/master/libbpf-tools/tcpstates.bpf.c>
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