图：BPF性能工具及其可见性

bpftrace安装请参考：bpftrace-install 。

1、查看哪些程序（如head,tail）正在打开什么文件：

# bpftrace -e 'tracepoint:syscalls:sys_enter_open { printf("%s %s\n", comm, str(args->filename)); }'
Attaching 1 probe...
head /usr/lib/locale/locale-archive
head /usr/share/locale/locale.alias
head /usr/lib/locale/en_US.UTF-8/LC_CTYPE
head /usr/lib/locale/en_US.utf8/LC_CTYPE
head /usr/lib64/gconv/gconv-modules.cache
head /usr/lib/locale/locale-archive
head /usr/share/locale/locale.alias
head /usr/lib/locale/en_US.UTF-8/LC_CTYPE
head /usr/lib/locale/en_US.utf8/LC_CTYPE
head /usr/lib64/gconv/gconv-modules.cache
tail /usr/lib/locale/locale-archive
tail /usr/share/locale/locale.alias
tail /usr/lib/locale/en_US.UTF-8/LC_CTYPE
tail /usr/lib/locale/en_US.utf8/LC_CTYPE
tail /usr/lib64/gconv/gconv-modules.cache
[...]

2、列出与open系统调用相关的跟踪点函数名：

# bpftrace -l 'tracepoint:syscalls:sys_enter_open*'
tracepoint:syscalls:sys_enter_open_by_handle_at
tracepoint:syscalls:sys_enter_open
tracepoint:syscalls:sys_enter_openat

3、工具开始运行至Ctrl + C退出，这个时段各个open相关跟踪点调用次数，这个摘要信息是由BPF程序在内核中高效计算出来的：

# bpftrace -e 'tracepoint:syscalls:sys_enter_open* { @[probe] = count(); }'
Attaching 3 probes...
^C

@[tracepoint:syscalls:sys_enter_open]: 576
@[tracepoint:syscalls:sys_enter_openat]: 1260

4、自带现成的脚本工具（没有的话请安装 zypper in bpftrace-tools），跟踪每个系统调用开始及结束位置：

# /usr/share/bpftrace/tools/opensnoop.bt
Attaching 6 probes...
Tracing open syscalls... Hit Ctrl-C to end.
PID    COMM               FD ERR PATH
4235   head               -1   2 tls/x86_64/x86_64/libc.so.6
4235   head               -1   2 tls/x86_64/libc.so.6
4235   head               -1   2 tls/x86_64/libc.so.6
4235   head               -1   2 tls/libc.so.6
4235   head               -1   2 x86_64/x86_64/libc.so.6
4235   head               -1   2 x86_64/libc.so.6
4235   head               -1   2 x86_64/libc.so.6
4235   head               -1   2 libc.so.6
4235   head                3   0 /etc/ld.so.cache
4235   head                3   0 /lib64/libc.so.6
4235   head               -1   2 /usr/lib/locale/locale-archive
4235   head                3   0 /usr/share/locale/locale.alias
4235   head               -1   2 /usr/lib/locale/en_US.UTF-8/LC_CTYPE
[...]

脚本内容如下：

# cat /usr/share/bpftrace/tools/opensnoop.bt
#!/usr/bin/bpftrace
/*
 * opensnoop    Trace open() syscalls.
 *              For Linux, uses bpftrace and eBPF.
 *
 * Also a basic example of bpftrace.
 *
 * USAGE: opensnoop.bt
 *
 * This is a bpftrace version of the bcc tool of the same name.
 *
 * Copyright 2018 Netflix, Inc.
 * Licensed under the Apache License, Version 2.0 (the "License")
 *
 * 08-Sep-2018  Brendan Gregg   Created this.
 */

BEGIN
{
        printf("Tracing open syscalls... Hit Ctrl-C to end.\n");
        printf("%-6s %-16s %4s %3s %s\n", "PID", "COMM", "FD", "ERR", "PATH");
}

tracepoint:syscalls:sys_enter_open,
tracepoint:syscalls:sys_enter_openat
{
        @filename[tid] = args->filename;
}

tracepoint:syscalls:sys_exit_open,
tracepoint:syscalls:sys_exit_openat
/@filename[tid]/
{
        $ret = args->ret;
        $fd = $ret > 0 ? $ret : -1;
        $errno = $ret > 0 ? 0 : - $ret;

        printf("%-6d %-16s %4d %3d %s\n", pid, comm, $fd, $errno,
            str(@filename[tid]));
        delete(@filename[tid]);
}

END
{
        clear(@filename);
}

--End--