mirror of
https://github.com/eunomia-bpf/bpf-developer-tutorial.git
synced 2026-02-04 02:34:16 +08:00
339 lines
29 KiB
HTML
339 lines
29 KiB
HTML
<!DOCTYPE HTML>
|
||
<html lang="en" class="light" dir="ltr">
|
||
<head>
|
||
<!-- Book generated using mdBook -->
|
||
<meta charset="UTF-8">
|
||
<title>lesson 2-kprobe-unlink - bpf-developer-tutorial</title>
|
||
|
||
|
||
<!-- Custom HTML head -->
|
||
|
||
<meta name="description" content="">
|
||
<meta name="viewport" content="width=device-width, initial-scale=1">
|
||
<meta name="theme-color" content="#ffffff">
|
||
|
||
<link rel="icon" href="../favicon.svg">
|
||
<link rel="shortcut icon" href="../favicon.png">
|
||
<link rel="stylesheet" href="../css/variables.css">
|
||
<link rel="stylesheet" href="../css/general.css">
|
||
<link rel="stylesheet" href="../css/chrome.css">
|
||
<link rel="stylesheet" href="../css/print.css" media="print">
|
||
|
||
<!-- Fonts -->
|
||
<link rel="stylesheet" href="../FontAwesome/css/font-awesome.css">
|
||
<link rel="stylesheet" href="../fonts/fonts.css">
|
||
|
||
<!-- Highlight.js Stylesheets -->
|
||
<link rel="stylesheet" href="../highlight.css">
|
||
<link rel="stylesheet" href="../tomorrow-night.css">
|
||
<link rel="stylesheet" href="../ayu-highlight.css">
|
||
|
||
<!-- Custom theme stylesheets -->
|
||
|
||
</head>
|
||
<body class="sidebar-visible no-js">
|
||
<div id="body-container">
|
||
<!-- Provide site root to javascript -->
|
||
<script>
|
||
var path_to_root = "../";
|
||
var default_theme = window.matchMedia("(prefers-color-scheme: dark)").matches ? "navy" : "light";
|
||
</script>
|
||
|
||
<!-- Work around some values being stored in localStorage wrapped in quotes -->
|
||
<script>
|
||
try {
|
||
var theme = localStorage.getItem('mdbook-theme');
|
||
var sidebar = localStorage.getItem('mdbook-sidebar');
|
||
|
||
if (theme.startsWith('"') && theme.endsWith('"')) {
|
||
localStorage.setItem('mdbook-theme', theme.slice(1, theme.length - 1));
|
||
}
|
||
|
||
if (sidebar.startsWith('"') && sidebar.endsWith('"')) {
|
||
localStorage.setItem('mdbook-sidebar', sidebar.slice(1, sidebar.length - 1));
|
||
}
|
||
} catch (e) { }
|
||
</script>
|
||
|
||
<!-- Set the theme before any content is loaded, prevents flash -->
|
||
<script>
|
||
var theme;
|
||
try { theme = localStorage.getItem('mdbook-theme'); } catch(e) { }
|
||
if (theme === null || theme === undefined) { theme = default_theme; }
|
||
var html = document.querySelector('html');
|
||
html.classList.remove('light')
|
||
html.classList.add(theme);
|
||
var body = document.querySelector('body');
|
||
body.classList.remove('no-js')
|
||
body.classList.add('js');
|
||
</script>
|
||
|
||
<input type="checkbox" id="sidebar-toggle-anchor" class="hidden">
|
||
|
||
<!-- Hide / unhide sidebar before it is displayed -->
|
||
<script>
|
||
var body = document.querySelector('body');
|
||
var sidebar = null;
|
||
var sidebar_toggle = document.getElementById("sidebar-toggle-anchor");
|
||
if (document.body.clientWidth >= 1080) {
|
||
try { sidebar = localStorage.getItem('mdbook-sidebar'); } catch(e) { }
|
||
sidebar = sidebar || 'visible';
|
||
} else {
|
||
sidebar = 'hidden';
|
||
}
|
||
sidebar_toggle.checked = sidebar === 'visible';
|
||
body.classList.remove('sidebar-visible');
|
||
body.classList.add("sidebar-" + sidebar);
|
||
</script>
|
||
|
||
<nav id="sidebar" class="sidebar" aria-label="Table of contents">
|
||
<div class="sidebar-scrollbox">
|
||
<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" class="active"><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 expanded "><a href="../5-uprobe-bashreadline/index.html"><strong aria-hidden="true">6.</strong> lesson 5-uprobe-bashreadline</a></li><li class="chapter-item expanded "><a href="../6-sigsnoop/index.html"><strong aria-hidden="true">7.</strong> lesson 6-sigsnoop</a></li><li class="chapter-item expanded "><a href="../7-execsnoop/index.html"><strong aria-hidden="true">8.</strong> lesson 7-execsnoop</a></li><li class="chapter-item expanded "><a href="../8-exitsnoop/index.html"><strong aria-hidden="true">9.</strong> lesson 8-execsnoop</a></li><li class="chapter-item expanded "><a href="../9-runqlat/index.html"><strong aria-hidden="true">10.</strong> lesson 9-runqlat</a></li><li class="chapter-item expanded "><a href="../10-hardirqs/index.html"><strong aria-hidden="true">11.</strong> lesson 10-hardirqs</a></li><li class="chapter-item expanded affix "><li class="part-title">进阶文档和示例</li><li class="chapter-item expanded "><a href="../11-bootstrap/index.html"><strong aria-hidden="true">12.</strong> lesson 11-bootstrap</a></li><li class="chapter-item expanded "><a href="../12-profile/index.html"><strong aria-hidden="true">13.</strong> lesson 12-profile</a></li><li class="chapter-item expanded "><a href="../13-tcpconnlat/index.html"><strong aria-hidden="true">14.</strong> lesson 13-tcpconnlat</a></li><li class="chapter-item expanded "><a href="../14-tcpstates/index.html"><strong aria-hidden="true">15.</strong> lesson 14-tcpstates</a></li><li class="chapter-item expanded "><a href="../15-javagc/index.html"><strong aria-hidden="true">16.</strong> lesson 15-javagc</a></li><li class="chapter-item expanded "><a href="../16-memleak/index.html"><strong aria-hidden="true">17.</strong> lesson 16-memleak</a></li><li class="chapter-item expanded "><a href="../17-biopattern/index.html"><strong aria-hidden="true">18.</strong> lesson 17-biopattern</a></li><li class="chapter-item expanded "><a href="../18-further-reading/index.html"><strong aria-hidden="true">19.</strong> lesson 18-further-reading</a></li><li class="chapter-item expanded "><a href="../19-lsm-connect/index.html"><strong aria-hidden="true">20.</strong> lesson 19-lsm-connect</a></li><li class="chapter-item expanded "><a href="../20-tc/index.html"><strong aria-hidden="true">21.</strong> lesson 20-tc</a></li><li class="chapter-item expanded "><a href="../21-xdp/index.html"><strong aria-hidden="true">22.</strong> lesson 21-xdp</a></li><li class="chapter-item expanded affix "><li class="part-title">高级主题</li><li class="chapter-item expanded "><a href="../22-android/index.html"><strong aria-hidden="true">23.</strong> 在 Android 上使用 eBPF 程序</a></li><li class="chapter-item expanded "><a href="../30-sslsniff/index.html"><strong aria-hidden="true">24.</strong> 使用 uprobe 捕获多种库的 SSL/TLS 明文数据</a></li><li class="chapter-item expanded "><a href="../23-http/index.html"><strong aria-hidden="true">25.</strong> 使用 eBPF socket filter 或 syscall trace 追踪 HTTP 请求和其他七层协议</a></li><li class="chapter-item expanded "><a href="../29-sockops/index.html"><strong aria-hidden="true">26.</strong> 使用 sockops 加速网络请求转发</a></li><li class="chapter-item expanded "><a href="../24-hide/index.html"><strong aria-hidden="true">27.</strong> 使用 eBPF 隐藏进程或文件信息</a></li><li class="chapter-item expanded "><a href="../25-signal/index.html"><strong aria-hidden="true">28.</strong> 使用 bpf_send_signal 发送信号终止进程</a></li><li class="chapter-item expanded "><a href="../26-sudo/index.html"><strong aria-hidden="true">29.</strong> 使用 eBPF 添加 sudo 用户</a></li><li class="chapter-item expanded "><a href="../27-replace/index.html"><strong aria-hidden="true">30.</strong> 使用 eBPF 替换任意程序读取或写入的文本</a></li><li class="chapter-item expanded "><a href="../28-detach/index.html"><strong aria-hidden="true">31.</strong> BPF 的生命周期：使用 Detached 模式在用户态应用退出后持续运行 eBPF 程序</a></li><li class="chapter-item expanded "><a href="../18-further-reading/ebpf-security.zh.html"><strong aria-hidden="true">32.</strong> eBPF 运行时的安全性与面临的挑战</a></li><li class="chapter-item expanded "><a href="../34-syscall/index.html"><strong aria-hidden="true">33.</strong> 使用 eBPF 修改系统调用参数</a></li><li class="chapter-item expanded "><a href="../35-user-ringbuf/index.html"><strong aria-hidden="true">34.</strong> eBPF开发实践：使用 user ring buffer 向内核异步发送信息</a></li><li class="chapter-item expanded "><a href="../36-userspace-ebpf/index.html"><strong aria-hidden="true">35.</strong> 用户空间 eBPF 运行时：深度解析与应用实践</a></li><li class="chapter-item expanded "><a href="../37-uprobe-rust/index.html"><strong aria-hidden="true">36.</strong> 使用 uprobe 追踪 Rust 应用程序</a></li><li class="chapter-item expanded "><a href="../38-btf-uprobe/index.html"><strong aria-hidden="true">37.</strong> 借助 eBPF 和 BTF，让用户态也能一次编译、到处运行</a></li><li class="chapter-item expanded affix "><li class="part-title">bcc 和 bpftrace 教程与文档</li><li class="chapter-item expanded "><a href="../bcc-documents/kernel-versions.html"><strong aria-hidden="true">38.</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">39.</strong> Kernel Configuration for BPF Features</a></li><li class="chapter-item expanded "><a href="../bcc-documents/reference_guide.html"><strong aria-hidden="true">40.</strong> bcc Reference Guide</a></li><li class="chapter-item expanded "><a href="../bcc-documents/special_filtering.html"><strong aria-hidden="true">41.</strong> Special Filtering</a></li><li class="chapter-item expanded "><a href="../bcc-documents/tutorial.html"><strong aria-hidden="true">42.</strong> bcc Tutorial</a></li><li class="chapter-item expanded "><a href="../bcc-documents/tutorial_bcc_python_developer.html"><strong aria-hidden="true">43.</strong> bcc Python Developer Tutorial</a></li><li class="chapter-item expanded "><a href="../bpftrace-tutorial/index.html"><strong aria-hidden="true">44.</strong> bpftrace Tutorial</a></li></ol>
|
||
</div>
|
||
<div id="sidebar-resize-handle" class="sidebar-resize-handle">
|
||
<div class="sidebar-resize-indicator"></div>
|
||
</div>
|
||
</nav>
|
||
|
||
<!-- Track and set sidebar scroll position -->
|
||
<script>
|
||
var sidebarScrollbox = document.querySelector('#sidebar .sidebar-scrollbox');
|
||
sidebarScrollbox.addEventListener('click', function(e) {
|
||
if (e.target.tagName === 'A') {
|
||
sessionStorage.setItem('sidebar-scroll', sidebarScrollbox.scrollTop);
|
||
}
|
||
}, { passive: true });
|
||
var sidebarScrollTop = sessionStorage.getItem('sidebar-scroll');
|
||
sessionStorage.removeItem('sidebar-scroll');
|
||
if (sidebarScrollTop) {
|
||
// preserve sidebar scroll position when navigating via links within sidebar
|
||
sidebarScrollbox.scrollTop = sidebarScrollTop;
|
||
} else {
|
||
// scroll sidebar to current active section when navigating via "next/previous chapter" buttons
|
||
var activeSection = document.querySelector('#sidebar .active');
|
||
if (activeSection) {
|
||
activeSection.scrollIntoView({ block: 'center' });
|
||
}
|
||
}
|
||
</script>
|
||
|
||
<div id="page-wrapper" class="page-wrapper">
|
||
|
||
<div class="page">
|
||
<div id="menu-bar-hover-placeholder"></div>
|
||
<div id="menu-bar" class="menu-bar sticky">
|
||
<div class="left-buttons">
|
||
<label id="sidebar-toggle" class="icon-button" for="sidebar-toggle-anchor" title="Toggle Table of Contents" aria-label="Toggle Table of Contents" aria-controls="sidebar">
|
||
<i class="fa fa-bars"></i>
|
||
</label>
|
||
<button id="theme-toggle" class="icon-button" type="button" title="Change theme" aria-label="Change theme" aria-haspopup="true" aria-expanded="false" aria-controls="theme-list">
|
||
<i class="fa fa-paint-brush"></i>
|
||
</button>
|
||
<ul id="theme-list" class="theme-popup" aria-label="Themes" role="menu">
|
||
<li role="none"><button role="menuitem" class="theme" id="light">Light</button></li>
|
||
<li role="none"><button role="menuitem" class="theme" id="rust">Rust</button></li>
|
||
<li role="none"><button role="menuitem" class="theme" id="coal">Coal</button></li>
|
||
<li role="none"><button role="menuitem" class="theme" id="navy">Navy</button></li>
|
||
<li role="none"><button role="menuitem" class="theme" id="ayu">Ayu</button></li>
|
||
</ul>
|
||
<button id="search-toggle" class="icon-button" type="button" title="Search. (Shortkey: s)" aria-label="Toggle Searchbar" aria-expanded="false" aria-keyshortcuts="S" aria-controls="searchbar">
|
||
<i class="fa fa-search"></i>
|
||
</button>
|
||
</div>
|
||
|
||
<h1 class="menu-title">bpf-developer-tutorial</h1>
|
||
|
||
<div class="right-buttons">
|
||
<a href="../print.html" title="Print this book" aria-label="Print this book">
|
||
<i id="print-button" class="fa fa-print"></i>
|
||
</a>
|
||
|
||
</div>
|
||
</div>
|
||
|
||
<div id="search-wrapper" class="hidden">
|
||
<form id="searchbar-outer" class="searchbar-outer">
|
||
<input type="search" id="searchbar" name="searchbar" placeholder="Search this book ..." aria-controls="searchresults-outer" aria-describedby="searchresults-header">
|
||
</form>
|
||
<div id="searchresults-outer" class="searchresults-outer hidden">
|
||
<div id="searchresults-header" class="searchresults-header"></div>
|
||
<ul id="searchresults">
|
||
</ul>
|
||
</div>
|
||
</div>
|
||
|
||
<!-- Apply ARIA attributes after the sidebar and the sidebar toggle button are added to the DOM -->
|
||
<script>
|
||
document.getElementById('sidebar-toggle').setAttribute('aria-expanded', sidebar === 'visible');
|
||
document.getElementById('sidebar').setAttribute('aria-hidden', sidebar !== 'visible');
|
||
Array.from(document.querySelectorAll('#sidebar a')).forEach(function(link) {
|
||
link.setAttribute('tabIndex', sidebar === 'visible' ? 0 : -1);
|
||
});
|
||
</script>
|
||
|
||
<div id="content" class="content">
|
||
<main>
|
||
<h1 id="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 class="header" href="#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">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></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二篇，在 eBPF 中使用 kprobe 捕获 unlink 系统调用。本文会先讲解关于 kprobes 的基本概念和技术背景，然后介绍如何在 eBPF 中使用 kprobe 捕获 unlink 系统调用。</p>
|
||
<h2 id="kprobes-技术背景"><a class="header" href="#kprobes-技术背景">kprobes 技术背景</a></h2>
|
||
<p>开发人员在内核或者模块的调试过程中，往往会需要要知道其中的一些函数有无被调用、何时被调用、执行是否正确以及函数的入参和返回值是什么等等。比较简单的做法是在内核代码对应的函数中添加日志打印信息，但这种方式往往需要重新编译内核或模块，重新启动设备之类的，操作较为复杂甚至可能会破坏原有的代码执行过程。</p>
|
||
<p>而利用 kprobes 技术，用户可以定义自己的回调函数，然后在内核或者模块中几乎所有的函数中（有些函数是不可探测的，例如kprobes自身的相关实现函数，后文会有详细说明）动态地插入探测点，当内核执行流程执行到指定的探测函数时，会调用该回调函数，用户即可收集所需的信息了，同时内核最后还会回到原本的正常执行流程。如果用户已经收集足够的信息，不再需要继续探测，则同样可以动态地移除探测点。因此 kprobes 技术具有对内核执行流程影响小和操作方便的优点。</p>
|
||
<p>kprobes 技术包括的3种探测手段分别时 kprobe、jprobe 和 kretprobe。首先 kprobe 是最基本的探测方式，是实现后两种的基础，它可以在任意的位置放置探测点（就连函数内部的某条指令处也可以），它提供了探测点的调用前、调用后和内存访问出错3种回调方式，分别是 <code>pre_handler</code>、<code>post_handler</code> 和 <code>fault_handler</code>，其中 <code>pre_handler</code> 函数将在被探测指令被执行前回调，<code>post_handler</code> 会在被探测指令执行完毕后回调（注意不是被探测函数），<code>fault_handler</code> 会在内存访问出错时被调用；jprobe 基于 kprobe 实现，它用于获取被探测函数的入参值；最后 kretprobe 从名字中就可以看出其用途了，它同样基于 kprobe 实现，用于获取被探测函数的返回值。</p>
|
||
<p>kprobes 的技术原理并不仅仅包含纯软件的实现方案，它也需要硬件架构提供支持。其中涉及硬件架构相关的是 CPU 的异常处理和单步调试技术，前者用于让程序的执行流程陷入到用户注册的回调函数中去，而后者则用于单步执行被探测点指令，因此并不是所有的架构均支持 kprobes。目前 kprobes 技术已经支持多种架构，包括 i386、x86_64、ppc64、ia64、sparc64、arm、ppc 和 mips（有些架构实现可能并不完全，具体可参考内核的 Documentation/kprobes.txt）。</p>
|
||
<p>kprobes 的特点与使用限制：</p>
|
||
<ol>
|
||
<li>kprobes 允许在同一个被探测位置注册多个 kprobe，但是目前 jprobe 却不可以；同时也不允许以其他的 jprobe 回调函数和 kprobe 的 <code>post_handler</code> 回调函数作为被探测点。</li>
|
||
<li>一般情况下，可以探测内核中的任何函数，包括中断处理函数。不过在 kernel/kprobes.c 和 arch/*/kernel/kprobes.c 程序中用于实现 kprobes 自身的函数是不允许被探测的，另外还有<code>do_page_fault</code> 和 <code>notifier_call_chain</code>；</li>
|
||
<li>如果以一个内联函数为探测点，则 kprobes 可能无法保证对该函数的所有实例都注册探测点。由于 gcc 可能会自动将某些函数优化为内联函数，因此可能无法达到用户预期的探测效果；</li>
|
||
<li>一个探测点的回调函数可能会修改被探测函数的运行上下文，例如通过修改内核的数据结构或者保存与<code>struct pt_regs</code>结构体中的触发探测器之前寄存器信息。因此 kprobes 可以被用来安装 bug 修复代码或者注入故障测试代码；</li>
|
||
<li>kprobes 会避免在处理探测点函数时再次调用另一个探测点的回调函数，例如在<code>printk()</code>函数上注册了探测点，而在它的回调函数中可能会再次调用<code>printk</code>函数，此时将不再触发<code>printk</code>探测点的回调，仅仅是增加了<code>kprobe</code>结构体中<code>nmissed</code>字段的数值；</li>
|
||
<li>在 kprobes 的注册和注销过程中不会使用 mutex 锁和动态的申请内存；</li>
|
||
<li>kprobes 回调函数的运行期间是关闭内核抢占的，同时也可能在关闭中断的情况下执行，具体要视CPU架构而定。因此不论在何种情况下，在回调函数中不要调用会放弃 CPU 的函数（如信号量、mutex 锁等）；</li>
|
||
<li>kretprobe 通过替换返回地址为预定义的 trampoline 的地址来实现，因此栈回溯和 gcc 内嵌函数<code>__builtin_return_address()</code>调用将返回 trampoline 的地址而不是真正的被探测函数的返回地址；</li>
|
||
<li>如果一个函数的调用次数和返回次数不相等，则在类似这样的函数上注册 kretprobe 将可能不会达到预期的效果，例如<code>do_exit()</code>函数会存在问题，而<code>do_execve()</code>函数和<code>do_fork()</code>函数不会；</li>
|
||
<li>当在进入和退出一个函数时，如果 CPU 运行在非当前任务所有的栈上，那么往该函数上注册 kretprobe 可能会导致不可预料的后果，因此，kprobes 不支持在 X86_64 的结构下为<code>__switch_to()</code>函数注册 kretprobe，将直接返回<code>-EINVAL</code>。</li>
|
||
</ol>
|
||
<h2 id="kprobe-示例"><a class="header" href="#kprobe-示例">kprobe 示例</a></h2>
|
||
<p>完整代码如下：</p>
|
||
<pre><code class="language-c">#include "vmlinux.h"
|
||
#include <bpf/bpf_helpers.h>
|
||
#include <bpf/bpf_tracing.h>
|
||
#include <bpf/bpf_core_read.h>
|
||
|
||
char LICENSE[] SEC("license") = "Dual BSD/GPL";
|
||
|
||
SEC("kprobe/do_unlinkat")
|
||
int BPF_KPROBE(do_unlinkat, int dfd, struct filename *name)
|
||
{
|
||
pid_t pid;
|
||
const char *filename;
|
||
|
||
pid = bpf_get_current_pid_tgid() >> 32;
|
||
filename = BPF_CORE_READ(name, name);
|
||
bpf_printk("KPROBE ENTRY pid = %d, filename = %s\n", pid, filename);
|
||
return 0;
|
||
}
|
||
|
||
SEC("kretprobe/do_unlinkat")
|
||
int BPF_KRETPROBE(do_unlinkat_exit, long ret)
|
||
{
|
||
pid_t pid;
|
||
|
||
pid = bpf_get_current_pid_tgid() >> 32;
|
||
bpf_printk("KPROBE EXIT: pid = %d, ret = %ld\n", pid, ret);
|
||
return 0;
|
||
}
|
||
</code></pre>
|
||
<p>这段代码是一个简单的 eBPF 程序，用于监测和捕获在 Linux 内核中执行的 unlink 系统调用。unlink 系统调用的功能是删除一个文件，这个 eBPF 程序通过使用 kprobe（内核探针）在<code>do_unlinkat</code>函数的入口和退出处放置钩子，实现对该系统调用的跟踪。</p>
|
||
<p>首先，我们导入必要的头文件，如 vmlinux.h，bpf_helpers.h，bpf_tracing.h 和 bpf_core_read.h。接着，我们定义许可证，以允许程序在内核中运行。</p>
|
||
<pre><code class="language-c">#include "vmlinux.h"
|
||
#include <bpf/bpf_helpers.h>
|
||
#include <bpf/bpf_tracing.h>
|
||
#include <bpf/bpf_core_read.h>
|
||
|
||
char LICENSE[] SEC("license") = "Dual BSD/GPL";
|
||
</code></pre>
|
||
<p>接下来，我们定义一个名为<code>BPF_KPROBE(do_unlinkat)</code>的 kprobe，当进入<code>do_unlinkat</code>函数时，它会被触发。该函数接受两个参数：<code>dfd</code>（文件描述符）和<code>name</code>（文件名结构体指针）。在这个 kprobe 中，我们获取当前进程的 PID（进程标识符），然后读取文件名。最后，我们使用<code>bpf_printk</code>函数在内核日志中打印 PID 和文件名。</p>
|
||
<pre><code class="language-c">SEC("kprobe/do_unlinkat")
|
||
int BPF_KPROBE(do_unlinkat, int dfd, struct filename *name)
|
||
{
|
||
pid_t pid;
|
||
const char *filename;
|
||
|
||
pid = bpf_get_current_pid_tgid() >> 32;
|
||
filename = BPF_CORE_READ(name, name);
|
||
bpf_printk("KPROBE ENTRY pid = %d, filename = %s\n", pid, filename);
|
||
return 0;
|
||
}
|
||
</code></pre>
|
||
<p>接下来，我们定义一个名为<code>BPF_KRETPROBE(do_unlinkat_exit)</code>的 kretprobe，当从<code>do_unlinkat</code>函数退出时，它会被触发。这个 kretprobe 的目的是捕获函数的返回值（ret）。我们再次获取当前进程的 PID，并使用<code>bpf_printk</code>函数在内核日志中打印 PID 和返回值。</p>
|
||
<pre><code class="language-c">SEC("kretprobe/do_unlinkat")
|
||
int BPF_KRETPROBE(do_unlinkat_exit, long ret)
|
||
{
|
||
pid_t pid;
|
||
|
||
pid = bpf_get_current_pid_tgid() >> 32;
|
||
bpf_printk("KPROBE EXIT: pid = %d, ret = %ld\n", pid, ret);
|
||
return 0;
|
||
}
|
||
</code></pre>
|
||
<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。</p>
|
||
<p>要编译这个程序，请使用 ecc 工具：</p>
|
||
<pre><code class="language-console">$ ecc kprobe-link.bpf.c
|
||
Compiling bpf object...
|
||
Packing ebpf object and config into package.json...
|
||
</code></pre>
|
||
<p>然后运行：</p>
|
||
<pre><code class="language-console">sudo ecli run package.json
|
||
</code></pre>
|
||
<p>在另外一个窗口中：</p>
|
||
<pre><code class="language-shell">touch test1
|
||
rm test1
|
||
touch test2
|
||
rm test2
|
||
</code></pre>
|
||
<p>在 /sys/kernel/debug/tracing/trace_pipe 文件中，应该能看到类似下面的 kprobe 演示输出：</p>
|
||
<pre><code class="language-shell">$ sudo cat /sys/kernel/debug/tracing/trace_pipe
|
||
rm-9346 [005] d..3 4710.951696: bpf_trace_printk: KPROBE ENTRY pid = 9346, filename = test1
|
||
rm-9346 [005] d..4 4710.951819: bpf_trace_printk: KPROBE EXIT: ret = 0
|
||
rm-9346 [005] d..3 4710.951852: bpf_trace_printk: KPROBE ENTRY pid = 9346, filename = test2
|
||
rm-9346 [005] d..4 4710.951895: bpf_trace_printk: KPROBE EXIT: ret = 0
|
||
</code></pre>
|
||
<h2 id="总结"><a class="header" href="#总结">总结</a></h2>
|
||
<p>通过本文的示例，我们学习了如何使用 eBPF 的 kprobe 和 kretprobe 捕获 unlink 系统调用。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>
|
||
<p>本文是 eBPF 入门开发实践教程的第二篇。下一篇文章将介绍如何在 eBPF 中使用 fentry 监测捕获 unlink 系统调用。</p>
|
||
<p>如果您希望学习更多关于 eBPF 的知识和实践，可以访问我们的教程代码仓库 <a href="https://github.com/eunomia-bpf/bpf-developer-tutorial">https://github.com/eunomia-bpf/bpf-developer-tutorial</a> 或网站 <a href="https://eunomia.dev/zh/tutorials/">https://eunomia.dev/zh/tutorials/</a> 以获取更多示例和完整的教程。</p>
|
||
|
||
</main>
|
||
|
||
<nav class="nav-wrapper" aria-label="Page navigation">
|
||
<!-- Mobile navigation buttons -->
|
||
<a rel="prev" href="../1-helloworld/index.html" class="mobile-nav-chapters previous" title="Previous chapter" aria-label="Previous chapter" aria-keyshortcuts="Left">
|
||
<i class="fa fa-angle-left"></i>
|
||
</a>
|
||
|
||
<a rel="next prefetch" href="../3-fentry-unlink/index.html" class="mobile-nav-chapters next" title="Next chapter" aria-label="Next chapter" aria-keyshortcuts="Right">
|
||
<i class="fa fa-angle-right"></i>
|
||
</a>
|
||
|
||
<div style="clear: both"></div>
|
||
</nav>
|
||
</div>
|
||
</div>
|
||
|
||
<nav class="nav-wide-wrapper" aria-label="Page navigation">
|
||
<a rel="prev" href="../1-helloworld/index.html" class="nav-chapters previous" title="Previous chapter" aria-label="Previous chapter" aria-keyshortcuts="Left">
|
||
<i class="fa fa-angle-left"></i>
|
||
</a>
|
||
|
||
<a rel="next prefetch" href="../3-fentry-unlink/index.html" class="nav-chapters next" title="Next chapter" aria-label="Next chapter" aria-keyshortcuts="Right">
|
||
<i class="fa fa-angle-right"></i>
|
||
</a>
|
||
</nav>
|
||
|
||
</div>
|
||
|
||
|
||
|
||
|
||
<script>
|
||
window.playground_copyable = true;
|
||
</script>
|
||
|
||
|
||
<script src="../elasticlunr.min.js"></script>
|
||
<script src="../mark.min.js"></script>
|
||
<script src="../searcher.js"></script>
|
||
|
||
<script src="../clipboard.min.js"></script>
|
||
<script src="../highlight.js"></script>
|
||
<script src="../book.js"></script>
|
||
|
||
<!-- Custom JS scripts -->
|
||
|
||
|
||
</div>
|
||
</body>
|
||
</html>
|