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From: Lee Eric <openlinuxsource@gmail.com>
Date: Wed, 15 Jul 2020 21:01:32 -0700
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Subject: Question about udp.sendmsg / udp.recvmsg
To: systemtap@sourceware.org
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Hi,

I have a quick question about what udp.sendmsg captures. I wrote a
small script to capture all processes are sending / receiving UDP
packets:

#!/usr/bin/env stap

probe udp.sendmsg {
printf("Req - time: [%s] pid: [%d] cmd: [%s] %s:%d => %s:%d\n",
ctime(gettimeofday_s()), pid(), execname(), saddr, sport, daddr,
dport)
}

probe udp.recvmsg {
printf("Resp - time: [%s] pid: [%d] cmd: [%s] %s:%d => %s:%d\n",
ctime(gettimeofday_s()), pid(), execname(), daddr, dport, saddr,
sport)
}

So I also triggered tcpdump to capture UDP traffic. I noticed the
systemtap shows some udp.sendmsg / udp.recvmsg probes are triggered
but there's no request on tcpdump side. So what possible reason can
cause this behavior? Is that normal?

Thanks.

Eric