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#!/usr/bin/python
#
# urandomread-explicit Example of instrumenting a kernel tracepoint.
# For Linux, uses BCC, BPF. Embedded C.
#
# This is an older example of instrumenting a tracepoint, which defines
# the argument struct and makes an explicit call to attach_tracepoint().
# See urandomread for a newer version that uses TRACEPOINT_PROBE().
#
# REQUIRES: Linux 4.7+ (BPF_PROG_TYPE_TRACEPOINT support).
#
# Test by running this, then in another shell, run:
# dd if=/dev/urandom of=/dev/null bs=1k count=5
#
# Copyright 2016 Netflix, Inc.
# Licensed under the Apache License, Version 2.0 (the "License")
from __future__ import print_function
from bcc import BPF
from bcc.utils import printb
# define BPF program
bpf_text = """
#include <uapi/linux/ptrace.h>
struct urandom_read_args {
// from /sys/kernel/debug/tracing/events/random/urandom_read/format
u64 __unused__;
u32 got_bits;
u32 pool_left;
u32 input_left;
};
int printarg(struct urandom_read_args *args) {
bpf_trace_printk("%d\\n", args->got_bits);
return 0;
}
"""
# load BPF program
b = BPF(text=bpf_text)
b.attach_tracepoint(tp="random:urandom_read", fn_name="printarg")
# header
print("%-18s %-16s %-6s %s" % ("TIME(s)", "COMM", "PID", "GOTBITS"))
# format output
while 1:
try:
(task, pid, cpu, flags, ts, msg) = b.trace_fields()
except ValueError:
continue
except KeyboardInterrupt:
exit()
printb(b"%-18.9f %-16s %-6d %s" % (ts, task, pid, msg))
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