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bpf-developer-tutorial
:wrap up Chapter 11 documentation
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yang miao
@@ -1 +1,156 @@
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## eBPF 入门实践教程：libbpf-bootstrap with user space
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## eBPF 入门实践教程：libbpf-bootstrap with user space
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# eBPF 入门开发实践指南十一篇：在 eBPF 中使用 bootstrap 跟踪exec()和exit()系统调用
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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。
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## 什么是bootstrap?
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Bootstrap是一个工具，它使用BPF（Berkeley Packet Filter）程序跟踪执行exec()系统调用（使用SEC（“tp/sched/sched_process_exec”）handle_exit BPF程序），这大致对应于新进程的生成（忽略fork（）部分）。此外，它还跟踪exit（）（使用SEC（“tp/sched/sched_process_exit”）handle_exit BPF程序）以了解每个进程何时退出。这两个BPF程序共同工作，允许捕获有关任何新进程的有趣信息，例如二进制文件的文件名，以及测量进程的生命周期并在进程死亡时收集有趣的统计信息，例如退出代码或消耗的资源量等。我认为这是深入了解内核内部并观察事物如何真正运作的良好起点。
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Bootstrap还使用argp API（libc的一部分）进行命令行参数解析。
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## Bootstrap
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```c
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// SPDX-License-Identifier: GPL-2.0 OR BSD-3-Clause
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/* Copyright (c) 2020 Facebook */
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#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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#include <bpf/bpf_core_read.h>
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#include "bootstrap.h"
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char LICENSE[] SEC("license") = "Dual BSD/GPL";
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struct {
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__uint(type, BPF_MAP_TYPE_HASH);
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__uint(max_entries, 8192);
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__type(key, pid_t);
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__type(value, u64);
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} exec_start SEC(".maps");
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struct {
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__uint(type, BPF_MAP_TYPE_RINGBUF);
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__uint(max_entries, 256 * 1024);
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} rb SEC(".maps");
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const volatile unsigned long long min_duration_ns = 0;
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SEC("tp/sched/sched_process_exec")
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int handle_exec(struct trace_event_raw_sched_process_exec *ctx)
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{
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struct task_struct *task;
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unsigned fname_off;
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struct event *e;
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pid_t pid;
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u64 ts;
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/* remember time exec() was executed for this PID */
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pid = bpf_get_current_pid_tgid() >> 32;
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ts = bpf_ktime_get_ns();
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bpf_map_update_elem(&exec_start, &pid, &ts, BPF_ANY);
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/* don't emit exec events when minimum duration is specified */
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if (min_duration_ns)
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return 0;
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/* reserve sample from BPF ringbuf */
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e = bpf_ringbuf_reserve(&rb, sizeof(*e), 0);
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if (!e)
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return 0;
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/* fill out the sample with data */
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task = (struct task_struct *)bpf_get_current_task();
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e->exit_event = false;
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e->pid = pid;
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e->ppid = BPF_CORE_READ(task, real_parent, tgid);
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bpf_get_current_comm(&e->comm, sizeof(e->comm));
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fname_off = ctx->__data_loc_filename & 0xFFFF;
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bpf_probe_read_str(&e->filename, sizeof(e->filename), (void *)ctx + fname_off);
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/* successfully submit it to user-space for post-processing */
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bpf_ringbuf_submit(e, 0);
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return 0;
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}
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SEC("tp/sched/sched_process_exit")
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int handle_exit(struct trace_event_raw_sched_process_template* ctx)
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{
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struct task_struct *task;
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struct event *e;
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pid_t pid, tid;
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u64 id, ts, *start_ts, duration_ns = 0;
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/* get PID and TID of exiting thread/process */
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id = bpf_get_current_pid_tgid();
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pid = id >> 32;
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tid = (u32)id;
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/* ignore thread exits */
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if (pid != tid)
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return 0;
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/* if we recorded start of the process, calculate lifetime duration */
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start_ts = bpf_map_lookup_elem(&exec_start, &pid);
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if (start_ts)
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duration_ns = bpf_ktime_get_ns() - *start_ts;
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else if (min_duration_ns)
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return 0;
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bpf_map_delete_elem(&exec_start, &pid);
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/* if process didn't live long enough, return early */
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if (min_duration_ns && duration_ns < min_duration_ns)
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return 0;
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/* reserve sample from BPF ringbuf */
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e = bpf_ringbuf_reserve(&rb, sizeof(*e), 0);
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if (!e)
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return 0;
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/* fill out the sample with data */
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task = (struct task_struct *)bpf_get_current_task();
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e->exit_event = true;
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e->duration_ns = duration_ns;
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e->pid = pid;
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e->ppid = BPF_CORE_READ(task, real_parent, tgid);
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e->exit_code = (BPF_CORE_READ(task, exit_code) >> 8) & 0xff;
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bpf_get_current_comm(&e->comm, sizeof(e->comm));
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/* send data to user-space for post-processing */
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bpf_ringbuf_submit(e, 0);
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return 0;
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}
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```
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这是一段使用BPF（Berkeley Packet Filter）的C程序，用于跟踪进程启动和退出事件，并显示有关它们的信息。BPF是一种强大的机制，允许您将称为BPF程序的小程序附加到Linux内核的各个部分。这些程序可用于过滤，监视或修改内核的行为。
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程序首先定义一些常量，并包含一些头文件。然后定义了一个名为env的struct，用于存储一些程序选项，例如详细模式和进程报告的最小持续时间。
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然后，程序定义了一个名为parse_arg的函数，用于解析传递给程序的命令行参数。它接受三个参数：一个表示正在解析的选项的整数key，一个表示选项参数的字符指针arg和一个表示当前解析状态的struct argp_state指针state。该函数处理选项并在env struct中设置相应的值。
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然后，程序定义了一个名为sig_handler的函数，当被调用时会将全局标志exiting设置为true。这用于在接收到信号时允许程序干净地退出。
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接下来，我们将继续描述这段代码中的其他部分。
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程序定义了一个名为exec_start的BPF map，它的类型为BPF_MAP_TYPE_HASH，最大条目数为8192，键类型为pid_t，值类型为u64。
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另外，程序还定义了一个名为rb的BPF map，它的类型为BPF_MAP_TYPE_RINGBUF，最大条目数为256 * 1024。
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程序还定义了一个名为min_duration_ns的常量，其值为0。
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程序定义了一个名为handle_exec的SEC（static evaluator of code）函数，它被附加到跟踪进程执行的BPF程序上。该函数记录为该PID执行exec（）的时间，并在指定了最小持续时间时不发出exec事件。如果未指定最小持续时间，则会从BPF ringbuf保留样本并使用数据填充样本，然后将其提交给用户空间进行后处理。
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程序还定义了一个名为handle_exit的SEC函数，它被附加到跟踪进程退出的BPF程序上。该函数会在确定PID和TID后计算进程的生命周期，然后根据min_duration_ns的值决定是否发出退出事件。如果进程的生命周期足够长，则会从BPF ringbuf保留样本并使用数据填充样本，然后将其提交给用户空间进行后处理。
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最后，主函数调用bpf_ringbuf_poll来轮询BPF ringbuf，并在接收到新的事件时处理该事件。这个函数会持续运行，直到全局标志exiting被设置为true，此时它会清理资源并退出。
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编译运行上述代码：
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```console
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$ ecc bootstrap.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 package.json
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Runing eBPF program...
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```
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## 总结
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这是一个使用BPF的C程序，用于跟踪进程的启动和退出事件，并显示有关这些事件的信息。它通过使用argp API来解析命令行参数，并使用BPF地图存储进程的信息，包括进程的PID和执行文件的文件名。程序还使用了SEC函数来附加BPF程序，以监视进程的执行和退出事件。最后，程序在终端中打印出启动和退出的进程信息。
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编译这个程序可以使用 ecc 工具，运行时可以使用 ecli 命令。更多的例子和详细的开发指南，请参考 eunomia-bpf 的官方文档：https://github.com/eunomia-bpf/eunomia-bpf
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112
11-bootstrap/bootstrap.bpf.c
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112
11-bootstrap/bootstrap.bpf.c
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@@ -0,0 +1,112 @@
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// SPDX-License-Identifier: GPL-2.0 OR BSD-3-Clause
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/* Copyright (c) 2020 Facebook */
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#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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#include <bpf/bpf_core_read.h>
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#include "bootstrap.h"
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char LICENSE[] SEC("license") = "Dual BSD/GPL";
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struct {
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__uint(type, BPF_MAP_TYPE_HASH);
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__uint(max_entries, 8192);
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__type(key, pid_t);
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__type(value, u64);
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} exec_start SEC(".maps");
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struct {
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__uint(type, BPF_MAP_TYPE_RINGBUF);
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__uint(max_entries, 256 * 1024);
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} rb SEC(".maps");
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const volatile unsigned long long min_duration_ns = 0;
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SEC("tp/sched/sched_process_exec")
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int handle_exec(struct trace_event_raw_sched_process_exec *ctx)
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{
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struct task_struct *task;
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unsigned fname_off;
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struct event *e;
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pid_t pid;
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u64 ts;
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/* remember time exec() was executed for this PID */
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pid = bpf_get_current_pid_tgid() >> 32;
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ts = bpf_ktime_get_ns();
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bpf_map_update_elem(&exec_start, &pid, &ts, BPF_ANY);
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/* don't emit exec events when minimum duration is specified */
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if (min_duration_ns)
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return 0;
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/* reserve sample from BPF ringbuf */
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e = bpf_ringbuf_reserve(&rb, sizeof(*e), 0);
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if (!e)
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return 0;
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/* fill out the sample with data */
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task = (struct task_struct *)bpf_get_current_task();
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e->exit_event = false;
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e->pid = pid;
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e->ppid = BPF_CORE_READ(task, real_parent, tgid);
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bpf_get_current_comm(&e->comm, sizeof(e->comm));
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fname_off = ctx->__data_loc_filename & 0xFFFF;
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bpf_probe_read_str(&e->filename, sizeof(e->filename), (void *)ctx + fname_off);
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/* successfully submit it to user-space for post-processing */
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bpf_ringbuf_submit(e, 0);
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return 0;
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}
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SEC("tp/sched/sched_process_exit")
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int handle_exit(struct trace_event_raw_sched_process_template* ctx)
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{
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struct task_struct *task;
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struct event *e;
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pid_t pid, tid;
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u64 id, ts, *start_ts, duration_ns = 0;
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/* get PID and TID of exiting thread/process */
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id = bpf_get_current_pid_tgid();
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pid = id >> 32;
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tid = (u32)id;
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/* ignore thread exits */
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if (pid != tid)
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return 0;
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/* if we recorded start of the process, calculate lifetime duration */
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start_ts = bpf_map_lookup_elem(&exec_start, &pid);
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if (start_ts)
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duration_ns = bpf_ktime_get_ns() - *start_ts;
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else if (min_duration_ns)
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return 0;
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bpf_map_delete_elem(&exec_start, &pid);
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/* if process didn't live long enough, return early */
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if (min_duration_ns && duration_ns < min_duration_ns)
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return 0;
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/* reserve sample from BPF ringbuf */
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e = bpf_ringbuf_reserve(&rb, sizeof(*e), 0);
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if (!e)
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return 0;
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/* fill out the sample with data */
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task = (struct task_struct *)bpf_get_current_task();
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e->exit_event = true;
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e->duration_ns = duration_ns;
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e->pid = pid;
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e->ppid = BPF_CORE_READ(task, real_parent, tgid);
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e->exit_code = (BPF_CORE_READ(task, exit_code) >> 8) & 0xff;
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bpf_get_current_comm(&e->comm, sizeof(e->comm));
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/* send data to user-space for post-processing */
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bpf_ringbuf_submit(e, 0);
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return 0;
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}
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19
11-bootstrap/bootstrap.h
Normal file
19
11-bootstrap/bootstrap.h
Normal file
@@ -0,0 +1,19 @@
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/* SPDX-License-Identifier: (LGPL-2.1 OR BSD-2-Clause) */
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/* Copyright (c) 2020 Facebook */
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#ifndef __BOOTSTRAP_H
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#define __BOOTSTRAP_H
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#define TASK_COMM_LEN 16
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#define MAX_FILENAME_LEN 127
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struct event {
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int pid;
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int ppid;
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unsigned exit_code;
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unsigned long long duration_ns;
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char comm[TASK_COMM_LEN];
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char filename[MAX_FILENAME_LEN];
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bool exit_event;
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};
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#endif /* __BOOTSTRAP_H */
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