#!/usr/bin/python
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# @lint-avoid-python-3-compatibility-imports
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#
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# ttysnoop Watch live output from a tty or pts device.
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# For Linux, uses BCC, eBPF. Embedded C.
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#
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# Due to a limited buffer size (see BUFSIZE), some commands (eg, a vim
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# session) are likely to be printed a little messed up.
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#
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# Copyright (c) 2016 Brendan Gregg.
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# Licensed under the Apache License, Version 2.0 (the "License")
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#
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# Idea: from ttywatcher.
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#
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# 15-Oct-2016 Brendan Gregg Created this.
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from __future__ import print_function
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from bcc import BPF
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import ctypes as ct
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from subprocess import call
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import argparse
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from sys import argv
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import sys
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from os import stat
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def usage():
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print("USAGE: %s [-Ch] {PTS | /dev/ttydev} # try -h for help" % argv[0])
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exit()
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# arguments
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examples = """examples:
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./ttysnoop /dev/pts/2 # snoop output from /dev/pts/2
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./ttysnoop 2 # snoop output from /dev/pts/2 (shortcut)
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./ttysnoop /dev/console # snoop output from the system console
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./ttysnoop /dev/tty0 # snoop output from /dev/tty0
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"""
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parser = argparse.ArgumentParser(
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description="Snoop output from a pts or tty device, eg, a shell",
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formatter_class=argparse.RawDescriptionHelpFormatter,
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epilog=examples)
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parser.add_argument("-C", "--noclear", action="store_true",
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help="don't clear the screen")
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parser.add_argument("device", default="-1",
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help="path to a tty device (eg, /dev/tty0) or pts number")
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parser.add_argument("--ebpf", action="store_true",
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help=argparse.SUPPRESS)
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args = parser.parse_args()
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debug = 0
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if args.device == "-1":
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usage()
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path = args.device
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if path.find('/') != 0:
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path = "/dev/pts/" + path
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try:
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pi = stat(path)
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except:
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print("Unable to read device %s. Exiting." % path)
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exit()
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# define BPF program
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bpf_text = """
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#include <uapi/linux/ptrace.h>
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#include <linux/fs.h>
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#define BUFSIZE 256
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struct data_t {
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int count;
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char buf[BUFSIZE];
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};
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BPF_PERF_OUTPUT(events);
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int kprobe__tty_write(struct pt_regs *ctx, struct file *file,
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const char __user *buf, size_t count)
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{
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if (file->f_inode->i_ino != PTS)
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return 0;
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// bpf_probe_read() can only use a fixed size, so truncate to count
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// in user space:
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struct data_t data = {};
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bpf_probe_read(&data.buf, BUFSIZE, (void *)buf);
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if (count > BUFSIZE)
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data.count = BUFSIZE;
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else
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data.count = count;
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events.perf_submit(ctx, &data, sizeof(data));
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return 0;
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};
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"""
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bpf_text = bpf_text.replace('PTS', str(pi.st_ino))
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if debug or args.ebpf:
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print(bpf_text)
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if args.ebpf:
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exit()
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# initialize BPF
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b = BPF(text=bpf_text)
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BUFSIZE = 256
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class Data(ct.Structure):
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_fields_ = [
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("count", ct.c_int),
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("buf", ct.c_char * BUFSIZE)
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]
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if not args.noclear:
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call("clear")
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# process event
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def print_event(cpu, data, size):
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event = ct.cast(data, ct.POINTER(Data)).contents
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print("%s" % event.buf[0:event.count].decode('utf-8', 'replace'), end="")
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sys.stdout.flush()
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# loop with callback to print_event
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b["events"].open_perf_buffer(print_event)
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while 1:
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b.perf_buffer_poll()
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