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<ol class="chapter"><li class="chapter-item expanded affix "><a href="../https://github.com/eunomia-bpf/bpf-developer-tutorial.html">https://github.com/eunomia-bpf/bpf-developer-tutorial</a></li><li class="chapter-item expanded affix "><li class="part-title">入门文档</li><li class="chapter-item expanded "><a href="../0-introduce/index.html"><strong aria-hidden="true">1.</strong> lesson 0-introduce</a></li><li class="chapter-item expanded "><a href="../1-helloworld/index.html"><strong aria-hidden="true">2.</strong> lesson 1-helloworld</a></li><li class="chapter-item expanded "><a href="../2-kprobe-unlink/index.html"><strong aria-hidden="true">3.</strong> lesson 2-kprobe-unlink</a></li><li class="chapter-item expanded "><a href="../3-fentry-unlink/index.html"><strong aria-hidden="true">4.</strong> lesson 3-fentry-unlink</a></li><li class="chapter-item expanded "><a href="../4-opensnoop/index.html"><strong aria-hidden="true">5.</strong> lesson 4-opensnoop</a></li><li class="chapter-item 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<h1 id="ebpf-入门开发实践教程八在-ebpf-中使用-exitsnoop-监控进程退出事件使用-ring-buffer-向用户态打印输出"><a class="header" href="#ebpf-入门开发实践教程八在-ebpf-中使用-exitsnoop-监控进程退出事件使用-ring-buffer-向用户态打印输出">eBPF 入门开发实践教程八:在 eBPF 中使用 exitsnoop 监控进程退出事件,使用 ring buffer 向用户态打印输出</a></h1>
<p>eBPF (Extended Berkeley Packet Filter) 是 Linux 内核上的一个强大的网络和性能分析工具。它允许开发者在内核运行时动态加载、更新和运行用户定义的代码。</p>
<p>本文是 eBPF 入门开发实践教程的第八篇,在 eBPF 中使用 exitsnoop 监控进程退出事件。</p>
<h2 id="ring-buffer"><a class="header" href="#ring-buffer">ring buffer</a></h2>
<p>现在有一个新的 BPF 数据结构可用eBPF 环形缓冲区ring buffer。它解决了 BPF perf buffer当今从内核向用户空间发送数据的事实上的标准的内存效率和事件重排问题同时达到或超过了它的性能。它既提供了与 perf buffer 兼容以方便迁移,又有新的保留/提交API具有更好的可用性。另外合成和真实世界的基准测试表明在几乎所有的情况下所以考虑将其作为从BPF程序向用户空间发送数据的默认选择。</p>
<h3 id="ebpf-ringbuf-vs-ebpf-perfbuf"><a class="header" href="#ebpf-ringbuf-vs-ebpf-perfbuf">eBPF ringbuf vs eBPF perfbuf</a></h3>
<p>只要 BPF 程序需要将收集到的数据发送到用户空间进行后处理和记录,它通常会使用 BPF perf bufferperfbuf来实现。Perfbuf 是每个CPU循环缓冲区的集合它允许在内核和用户空间之间有效地交换数据。它在实践中效果很好但由于其按CPU设计它有两个主要的缺点在实践中被证明是不方便的内存的低效使用和事件的重新排序。</p>
<p>为了解决这些问题从Linux 5.8开始BPF提供了一个新的BPF数据结构BPF map。BPF环形缓冲区ringbuf。它是一个多生产者、单消费者MPSC队列可以同时在多个CPU上安全共享。</p>
<p>BPF ringbuf 支持来自 BPF perfbuf 的熟悉的功能:</p>
<ul>
<li>变长的数据记录。</li>
<li>能够通过内存映射区域有效地从用户空间读取数据,而不需要额外的内存拷贝和/或进入内核的系统调用。</li>
<li>既支持epoll通知又能以绝对最小的延迟进行忙环操作。</li>
</ul>
<p>同时BPF ringbuf解决了BPF perfbuf的以下问题:</p>
<ul>
<li>内存开销。</li>
<li>数据排序。</li>
<li>浪费的工作和额外的数据复制。</li>
</ul>
<h2 id="exitsnoop"><a class="header" href="#exitsnoop">exitsnoop</a></h2>
<p>本文是 eBPF 入门开发实践教程的第八篇,在 eBPF 中使用 exitsnoop 监控进程退出事件,并使用 ring buffer 向用户态打印输出。</p>
<p>使用 ring buffer 向用户态打印输出的步骤和 perf buffer 类似,首先需要定义一个头文件:</p>
<p>头文件exitsnoop.h</p>
<pre><code class="language-c">#ifndef __BOOTSTRAP_H
#define __BOOTSTRAP_H
#define TASK_COMM_LEN 16
#define MAX_FILENAME_LEN 127
struct event {
int pid;
int ppid;
unsigned exit_code;
unsigned long long duration_ns;
char comm[TASK_COMM_LEN];
};
#endif /* __BOOTSTRAP_H */
</code></pre>
<p>源文件exitsnoop.bpf.c</p>
<pre><code class="language-c">#include &quot;vmlinux.h&quot;
#include &lt;bpf/bpf_helpers.h&gt;
#include &lt;bpf/bpf_tracing.h&gt;
#include &lt;bpf/bpf_core_read.h&gt;
#include &quot;exitsnoop.h&quot;
char LICENSE[] SEC(&quot;license&quot;) = &quot;Dual BSD/GPL&quot;;
struct {
__uint(type, BPF_MAP_TYPE_RINGBUF);
__uint(max_entries, 256 * 1024);
} rb SEC(&quot;.maps&quot;);
SEC(&quot;tp/sched/sched_process_exit&quot;)
int handle_exit(struct trace_event_raw_sched_process_template* ctx)
{
struct task_struct *task;
struct event *e;
pid_t pid, tid;
u64 id, ts, *start_ts, start_time = 0;
/* get PID and TID of exiting thread/process */
id = bpf_get_current_pid_tgid();
pid = id &gt;&gt; 32;
tid = (u32)id;
/* ignore thread exits */
if (pid != tid)
return 0;
/* reserve sample from BPF ringbuf */
e = bpf_ringbuf_reserve(&amp;rb, sizeof(*e), 0);
if (!e)
return 0;
/* fill out the sample with data */
task = (struct task_struct *)bpf_get_current_task();
start_time = BPF_CORE_READ(task, start_time);
e-&gt;duration_ns = bpf_ktime_get_ns() - start_time;
e-&gt;pid = pid;
e-&gt;ppid = BPF_CORE_READ(task, real_parent, tgid);
e-&gt;exit_code = (BPF_CORE_READ(task, exit_code) &gt;&gt; 8) &amp; 0xff;
bpf_get_current_comm(&amp;e-&gt;comm, sizeof(e-&gt;comm));
/* send data to user-space for post-processing */
bpf_ringbuf_submit(e, 0);
return 0;
}
</code></pre>
<p>这段代码展示了如何使用 exitsnoop 监控进程退出事件并使用 ring buffer 向用户态打印输出:</p>
<ol>
<li>首先,我们引入所需的头文件和 exitsnoop.h。</li>
<li>定义一个名为 &quot;LICENSE&quot; 的全局变量,内容为 &quot;Dual BSD/GPL&quot;,这是 eBPF 程序的许可证要求。</li>
<li>定义一个名为 rb 的 BPF_MAP_TYPE_RINGBUF 类型的映射,它将用于将内核空间的数据传输到用户空间。指定 max_entries 为 256 * 1024代表 ring buffer 的最大容量。</li>
<li>定义一个名为 handle_exit 的 eBPF 程序,它将在进程退出事件触发时执行。传入一个名为 ctx 的 trace_event_raw_sched_process_template 结构体指针作为参数。</li>
<li>使用 bpf_get_current_pid_tgid() 函数获取当前任务的 PID 和 TID。对于主线程PID 和 TID 相同;对于子线程,它们是不同的。我们只关心进程(主线程)的退出,因此在 PID 和 TID 不同时返回 0忽略子线程退出事件。</li>
<li>使用 bpf_ringbuf_reserve 函数为事件结构体 e 在 ring buffer 中预留空间。如果预留失败,返回 0。</li>
<li>使用 bpf_get_current_task() 函数获取当前任务的 task_struct 结构指针。</li>
<li>将进程相关信息填充到预留的事件结构体 e 中包括进程持续时间、PID、PPID、退出代码以及进程名称。</li>
<li>最后,使用 bpf_ringbuf_submit 函数将填充好的事件结构体 e 提交到 ring buffer之后在用户空间进行处理和输出。</li>
</ol>
<p>这个示例展示了如何使用 exitsnoop 和 ring buffer 在 eBPF 程序中捕获进程退出事件并将相关信息传输到用户空间。这对于分析进程退出原因和监控系统行为非常有用。</p>
<h2 id="compile-and-run"><a class="header" href="#compile-and-run">Compile and Run</a></h2>
<p>eunomia-bpf 是一个结合 Wasm 的开源 eBPF 动态加载运行时和开发工具链,它的目的是简化 eBPF 程序的开发、构建、分发、运行。可以参考 <a href="https://github.com/eunomia-bpf/eunomia-bpf">https://github.com/eunomia-bpf/eunomia-bpf</a> 下载和安装 ecc 编译工具链和 ecli 运行时。我们使用 eunomia-bpf 编译运行这个例子。</p>
<p>Compile:</p>
<pre><code class="language-shell">docker run -it -v `pwd`/:/src/ ghcr.io/eunomia-bpf/ecc-`uname -m`:latest
</code></pre>
<p>Or</p>
<pre><code class="language-console">$ ecc exitsnoop.bpf.c exitsnoop.h
Compiling bpf object...
Generating export types...
Packing ebpf object and config into package.json...
</code></pre>
<p>Run:</p>
<pre><code class="language-console">$ sudo ./ecli run package.json
TIME PID PPID EXIT_CODE DURATION_NS COMM
21:40:09 42050 42049 0 0 which
21:40:09 42049 3517 0 0 sh
21:40:09 42052 42051 0 0 ps
21:40:09 42051 3517 0 0 sh
21:40:09 42055 42054 0 0 sed
21:40:09 42056 42054 0 0 cat
21:40:09 42057 42054 0 0 cat
21:40:09 42058 42054 0 0 cat
21:40:09 42059 42054 0 0 cat
</code></pre>
<h2 id="总结"><a class="header" href="#总结">总结</a></h2>
<p>本文介绍了如何使用 eunomia-bpf 开发一个简单的 BPF 程序,该程序可以监控 Linux 系统中的进程退出事件, 并将捕获的事件通过 ring buffer 发送给用户空间程序。在本文中,我们使用 eunomia-bpf 编译运行了这个例子。</p>
<p>为了更好地理解和实践 eBPF 编程,我们建议您阅读 eunomia-bpf 的官方文档:<a href="https://github.com/eunomia-bpf/eunomia-bpf">https://github.com/eunomia-bpf/eunomia-bpf</a> 。此外,我们还为您提供了完整的教程和源代码,您可以在 <a href="https://github.com/eunomia-bpf/bpf-developer-tutorial">https://github.com/eunomia-bpf/bpf-developer-tutorial</a> 中查看和学习。希望本教程能够帮助您顺利入门 eBPF 开发,并为您的进一步学习和实践提供有益的参考。</p>
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