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<ol class="chapter"><li class="chapter-item expanded affix "><li class="part-title">eBPF 实践教程：基于 libbpf 和 CO-RE</li><li class="chapter-item expanded "><a href="../0-introduce/index.html"><strong aria-hidden="true">1.</strong> eBPF 入门开发实践教程一：介绍 eBPF 的基本概念、常见的开发工具</a></li><li class="chapter-item expanded "><a href="../1-helloworld/index.html"><strong aria-hidden="true">2.</strong> eBPF 入门开发实践教程二：Hello World，基本框架和开发流程</a></li><li class="chapter-item expanded "><a href="../2-kprobe-unlink/index.html"><strong aria-hidden="true">3.</strong> eBPF 入门开发实践教程二：在 eBPF 中使用 kprobe 监测捕获 unlink 系统调用</a></li><li class="chapter-item expanded "><a href="../3-fentry-unlink/index.html" class="active"><strong aria-hidden="true">4.</strong> eBPF 入门开发实践教程三：在 eBPF 中使用 fentry 监测捕获 unlink 系统调用</a></li><li class="chapter-item expanded "><a href="../4-opensnoop/index.html"><strong aria-hidden="true">5.</strong> eBPF 入门开发实践教程四：在 eBPF 中捕获进程打开文件的系统调用集合，使用全局变量过滤进程 pid</a></li><li class="chapter-item expanded "><a href="../5-uprobe-bashreadline/index.html"><strong aria-hidden="true">6.</strong> eBPF 入门开发实践教程五：在 eBPF 中使用 uprobe 捕获 bash 的 readline 函数调用</a></li><li class="chapter-item expanded "><a href="../6-sigsnoop/index.html"><strong aria-hidden="true">7.</strong> eBPF 入门开发实践教程六：捕获进程发送信号的系统调用集合，使用 hash map 保存状态</a></li><li class="chapter-item expanded "><a href="../7-execsnoop/index.html"><strong aria-hidden="true">8.</strong> eBPF 入门实践教程七：捕获进程执行/退出时间，通过 perf event array 向用户态打印输出</a></li><li class="chapter-item expanded "><a href="../8-exitsnoop/index.html"><strong aria-hidden="true">9.</strong> 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></li><li class="chapter-item expanded "><a href="../9-runqlat/index.html"><strong aria-hidden="true">10.</strong> eBPF 入门开发实践教程九：一个 Linux 内核 BPF 程序，通过柱状图来总结调度程序运行队列延迟，显示任务等待运行在 CPU 上的时间长度</a></li><li class="chapter-item expanded "><a href="../10-hardirqs/index.html"><strong aria-hidden="true">11.</strong> eBPF 入门开发实践教程十：在 eBPF 中使用 hardirqs 或 softirqs 捕获中断事件</a></li><li class="chapter-item expanded "><a href="../11-bootstrap/index.html"><strong aria-hidden="true">12.</strong> eBPF 入门开发实践教程十一：在 eBPF 中使用 bootstrap 开发用户态程序并跟踪 exec() 和 exit() 系统调用</a></li><li class="chapter-item expanded "><a href="../13-tcpconnlat/index.html"><strong aria-hidden="true">13.</strong> eBPF入门实践教程：使用 libbpf-bootstrap 开发程序统计 TCP 连接延时</a></li><li class="chapter-item expanded "><a href="../13-tcpconnlat/tcpconnlat.html"><strong aria-hidden="true">14.</strong> eBPF 入门实践教程：编写 eBPF 程序 tcpconnlat 测量 tcp 连接延时</a></li><li class="chapter-item expanded "><a href="../14-tcpstates/index.html"><strong aria-hidden="true">15.</strong> eBPF入门实践教程：使用 libbpf-bootstrap 开发程序统计 TCP 连接延时</a></li><li class="chapter-item expanded "><a href="../15-tcprtt/index.html"><strong aria-hidden="true">16.</strong> eBPF 入门实践教程：编写 eBPF 程序 Tcprtt 测量 TCP 连接的往返时间</a></li><li class="chapter-item expanded "><a href="../16-memleak/index.html"><strong aria-hidden="true">17.</strong> eBPF 入门实践教程：编写 eBPF 程序 Memleak 监控内存泄漏</a></li><li class="chapter-item expanded "><a href="../17-biopattern/index.html"><strong aria-hidden="true">18.</strong> eBPF 入门实践教程：编写 eBPF 程序 Biopattern: 统计随机/顺序磁盘 I/O</a></li><li class="chapter-item expanded "><a href="../18-further-reading/index.html"><strong aria-hidden="true">19.</strong> 更多的参考资料</a></li><li class="chapter-item expanded "><a href="../19-lsm-connect/index.html"><strong aria-hidden="true">20.</strong> eBPF 入门实践教程：使用 LSM 进行安全检测防御</a></li><li class="chapter-item expanded "><a href="../20-tc/index.html"><strong aria-hidden="true">21.</strong> eBPF 入门实践教程：使用 eBPF 进行 tc 流量控制</a></li><li class="chapter-item expanded affix "><li class="part-title">bcc 开发者教程</li><li class="chapter-item expanded "><a href="../bcc-documents/kernel-versions.html"><strong aria-hidden="true">22.</strong> BPF Features by Linux Kernel Version</a></li><li class="chapter-item expanded "><a href="../bcc-documents/kernel_config.html"><strong aria-hidden="true">23.</strong> Kernel Configuration for BPF Features</a></li><li class="chapter-item expanded "><a href="../bcc-documents/reference_guide.html"><strong aria-hidden="true">24.</strong> bcc Reference Guide</a></li><li class="chapter-item expanded "><a href="../bcc-documents/special_filtering.html"><strong aria-hidden="true">25.</strong> Special Filtering</a></li><li class="chapter-item expanded "><a href="../bcc-documents/tutorial.html"><strong aria-hidden="true">26.</strong> bcc Tutorial</a></li><li class="chapter-item expanded "><a href="../bcc-documents/tutorial_bcc_python_developer.html"><strong aria-hidden="true">27.</strong> bcc Python Developer Tutorial</a></li></ol>
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<h1 id="ebpf-入门开发实践教程三在-ebpf-中使用-fentry-监测捕获-unlink-系统调用"><a class="header" href="#ebpf-入门开发实践教程三在-ebpf-中使用-fentry-监测捕获-unlink-系统调用">eBPF 入门开发实践教程三：在 eBPF 中使用 fentry 监测捕获 unlink 系统调用</a></h1>
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<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>
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<p>本文是 eBPF 入门开发实践教程的第三篇，在 eBPF 中使用 fentry 捕获 unlink 系统调用。</p>
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<h2 id="fentry"><a class="header" href="#fentry">Fentry</a></h2>
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<p>fentry（function entry）和fexit（function exit）是eBPF（扩展的伯克利包过滤器）中的两种探针类型，用于在Linux内核函数的入口和退出处进行跟踪。它们允许开发者在内核函数执行的特定阶段收集信息、修改参数或观察返回值。这种跟踪和监控功能在性能分析、故障排查和安全分析等场景中非常有用。</p>
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<p>与 kprobes 相比，fentry 和 fexit 程序有更高的性能和可用性。在这个例子中，我们可以直接访问函数的指针参数，就像在普通的 C 代码中一样，而不需要使用各种读取帮助程序。fexit 和 kretprobe 程序最大的区别在于，fexit 程序可以访问函数的输入参数和返回值，而 kretprobe 只能访问返回值。从 5.5 内核开始，fentry 和 fexit 对 eBPF 程序可用。</p>
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<pre><code class="language-c">#include "vmlinux.h"
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#include <bpf/bpf_helpers.h>
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#include <bpf/bpf_tracing.h>
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char LICENSE[] SEC("license") = "Dual BSD/GPL";
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SEC("fentry/do_unlinkat")
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int BPF_PROG(do_unlinkat, int dfd, struct filename *name)
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{
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pid_t pid;
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pid = bpf_get_current_pid_tgid() >> 32;
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bpf_printk("fentry: pid = %d, filename = %s\n", pid, name->name);
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return 0;
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}
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SEC("fexit/do_unlinkat")
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int BPF_PROG(do_unlinkat_exit, int dfd, struct filename *name, long ret)
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{
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pid_t pid;
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pid = bpf_get_current_pid_tgid() >> 32;
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bpf_printk("fexit: pid = %d, filename = %s, ret = %ld\n", pid, name->name, ret);
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return 0;
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}
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</code></pre>
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<p>这段程序是用C语言编写的eBPF（扩展的伯克利包过滤器）程序，它使用BPF的fentry和fexit探针来跟踪Linux内核函数do_unlinkat。在这个教程中，我们将以这段程序作为示例，让您学会如何在eBPF中使用fentry监测捕获unlink系统调用。</p>
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<p>程序包含以下部分：</p>
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<ol>
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<li>包含头文件：包括vmlinux.h（用于访问内核数据结构）、bpf/bpf_helpers.h（包含eBPF帮助函数）、bpf/bpf_tracing.h（用于eBPF跟踪相关功能）。</li>
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<li>定义许可证：这里定义了一个名为LICENSE的字符数组，包含许可证信息"Dual BSD/GPL"。</li>
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<li>定义fentry探针：我们定义了一个名为BPF_PROG(do_unlinkat)的fentry探针，该探针在do_unlinkat函数的入口处被触发。这个探针获取当前进程的PID（进程ID）并将其与文件名一起打印到内核日志。</li>
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<li>定义fexit探针：我们还定义了一个名为BPF_PROG(do_unlinkat_exit)的fexit探针，该探针在do_unlinkat函数的退出处被触发。与fentry探针类似，这个探针也会获取当前进程的PID并将其与文件名和返回值一起打印到内核日志。</li>
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</ol>
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<p>通过这个示例，您可以学习如何在eBPF中使用fentry和fexit探针来监控和捕获内核函数调用，例如在本教程中的unlink系统调用。</p>
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<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>
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<p>编译运行上述代码：</p>
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<pre><code class="language-console">$ ecc fentry-link.bpf.c
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Compiling bpf object...
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Packing ebpf object and config into package.json...
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$ sudo ecli run package.json
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Runing eBPF program...
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</code></pre>
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<p>在另外一个窗口中：</p>
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<pre><code class="language-shell">touch test_file
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rm test_file
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touch test_file2
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rm test_file2
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</code></pre>
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<p>运行这段程序后，可以通过查看 /sys/kernel/debug/tracing/trace_pipe 文件来查看 eBPF 程序的输出：</p>
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<pre><code class="language-console">$ sudo cat /sys/kernel/debug/tracing/trace_pipe
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rm-9290 [004] d..2 4637.798698: bpf_trace_printk: fentry: pid = 9290, filename = test_file
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rm-9290 [004] d..2 4637.798843: bpf_trace_printk: fexit: pid = 9290, filename = test_file, ret = 0
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rm-9290 [004] d..2 4637.798698: bpf_trace_printk: fentry: pid = 9290, filename = test_file2
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rm-9290 [004] d..2 4637.798843: bpf_trace_printk: fexit: pid = 9290, filename = test_file2, ret = 0
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</code></pre>
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<h2 id="总结"><a class="header" href="#总结">总结</a></h2>
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<p>这段程序是一个 eBPF 程序，通过使用 fentry 和 fexit 捕获 do_unlinkat 和 do_unlinkat_exit 函数，并通过使用 bpf_get_current_pid_tgid 和 bpf_printk 函数获取调用 do_unlinkat 的进程 ID、文件名和返回值，并在内核日志中打印出来。</p>
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<p>编译这个程序可以使用 ecc 工具，运行时可以使用 ecli 命令，并通过查看 /sys/kernel/debug/tracing/trace_pipe 文件查看 eBPF 程序的输出。更多的例子和详细的开发指南，请参考 eunomia-bpf 的官方文档：<a href="https://github.com/eunomia-bpf/eunomia-bpf">https://github.com/eunomia-bpf/eunomia-bpf</a></p>
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<p>完整的教程和源代码已经全部开源，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。</p>
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