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Date: Sat, 9 Jan 2021 20:47:38 +0200
From: Konstantin Belousov <kostikbel@gmail.com>
To: Vasily Postnicov <shamaz.mazum@gmail.com>
Cc: Mark Johnston <markj@freebsd.org>, freebsd-net@freebsd.org
Subject: Re: DNS using Name Service Switch module and Casper
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On Sat, Jan 09, 2021 at 08:25:46PM +0300, Vasily Postnicov wrote:
> Brilliant! It took me almost a day to dive into ZeroMQ to reassure
> myself that there is nothing wrong with it. When I tried to write
> minimal test programs which call fork after pthread_create() in all
> combinations. When I realized that NSS stub module is what I need.
> 
> Instructions:
> 
> 1) Compile NSS stub module: cc -shared -fPIC -pthread -o
> nss_zerodns.so.1 test.c (Note '.1' at the end).
> 2) Copy nss_zerodns.so.1 to /usr/local/lib
> 3) Apply the patch src_sbin_ping_main.c to ping source code. With this
> patch ping will not quit too early when the initial call to
> getaddrinfo() fails.
> 4) Add stub module to /etc/nsswitch.conf: edit 'hosts' line to be
> 'hosts: files dns zerodns'
> 5) Ping non-existent host, like 'ping foo.bar'
> 6) Ping will hang. The child process which it creates cannot be killed
> even with killall -9 ping

This is exactly what I do not want.  Provide a standalone binary (or
binaries) that can be just run and demonstrate the issue.  Without
editing nsswitch.conf or patching ping.