#!/usr/bin/env python

from bcc import BPF

# load BPF program
b = BPF(text="""
#include <uapi/linux/ptrace.h>
#include <linux/blkdev.h>

BPF_HASH(last);

int do_trace(struct pt_regs *ctx) {
	u64 ts, *tsp, delta, key = 0;

	// attempt to read stored timestamp
	tsp = last.lookup(&key);
	if (tsp != 0) {
		delta = bpf_ktime_get_ns() - *tsp;
		if (delta < 1000000000) {
			// output if time is less than 1 second
			bpf_trace_printk("%d\\n", delta / 1000000);
		}
		last.delete(&key);
	}

	// update stored timestamp
	ts = bpf_ktime_get_ns();
	last.update(&key, &ts);
	return 0;
}
""")

b.attach_kprobe(event="sys_sync", fn_name="do_trace")
print("Tracing for quick sync's... Ctrl-C to end")

# format output
start = 0
while 1:
    (task, pid, cpu, flags, ts, ms) = b.trace_fields()
    if start == 0:
        start = ts
    ts = ts - start
    print("At time %.2f s: multiple syncs detected, last %s ms ago" % (ts, ms))