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81 lines
2.1 KiB
Markdown
81 lines
2.1 KiB
Markdown
## eBPF 入门实践教程：编写 eBPF 程序 syscount 监控慢系统调用
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### 背景
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`syscount` 可以统计系统或者某个进程发生的各类syscall的总数或者时耗时。
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### 实现原理
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`syscount` 的实现逻辑非常直观，他在 `sys_enter` 和 `sys_exit` 这两个 `tracepoint` 下挂载了
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执行函数。
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```c
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SEC("tracepoint/raw_syscalls/sys_enter")
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int sys_enter(struct trace_event_raw_sys_enter *args)
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{
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u64 id = bpf_get_current_pid_tgid();
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pid_t pid = id >> 32;
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u32 tid = id;
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u64 ts;
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if (filter_cg && !bpf_current_task_under_cgroup(&cgroup_map, 0))
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return 0;
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if (filter_pid && pid != filter_pid)
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return 0;
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ts = bpf_ktime_get_ns();
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bpf_map_update_elem(&start, &tid, &ts, 0);
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return 0;
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}
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SEC("tracepoint/raw_syscalls/sys_exit")
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int sys_exit(struct trace_event_raw_sys_exit *args)
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{
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if (filter_cg && !bpf_current_task_under_cgroup(&cgroup_map, 0))
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return 0;
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u64 id = bpf_get_current_pid_tgid();
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static const struct data_t zero;
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pid_t pid = id >> 32;
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struct data_t *val;
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u64 *start_ts, lat = 0;
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u32 tid = id;
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u32 key;
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/* this happens when there is an interrupt */
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if (args->id == -1)
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return 0;
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if (filter_pid && pid != filter_pid)
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return 0;
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if (filter_failed && args->ret >= 0)
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return 0;
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if (filter_errno && args->ret != -filter_errno)
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return 0;
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if (measure_latency) {
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start_ts = bpf_map_lookup_elem(&start, &tid);
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if (!start_ts)
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return 0;
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lat = bpf_ktime_get_ns() - *start_ts;
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}
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key = (count_by_process) ? pid : args->id;
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val = bpf_map_lookup_or_try_init(&data, &key, &zero);
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if (val) {
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__sync_fetch_and_add(&val->count, 1);
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if (count_by_process)
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save_proc_name(val);
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if (measure_latency)
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__sync_fetch_and_add(&val->total_ns, lat);
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}
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return 0;
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}
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```
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当syscall发生时，`syscount`会记录其tid和发生的时间并存入map中。在syscall完成时，`syscount` 会根据用户
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的需求，统计syscall持续的时间，或者是发生的次数。
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### Eunomia中使用方式
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### 总结
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`sycount` 使得用户可以较为方便的追踪某个进程或者是系统内系统调用发生的情况。 |