kseltest: bpf: test_lwt_ip_encap.sh: Why -l used in test_gso

[Prabhakar Kushwaha <prabhakar.pkin@gmail.com>]

Hi All,

I am trying to understand test_gso test for IPv4 and IPv6 with following 
piece of code

       # listen on IPv*_DST, capture TCP into $TMPFILE
         if [ "${PROTO}" == "IPv4" ] ; then
                 IP_DST=${IPv4_DST}
                 ip netns exec ${NS3} bash -c \
                        "nc -4 -l -s ${IPv4_DST} -p 9000 > ${TMPFILE} &"
         elif [ "${PROTO}" == "IPv6" ] ; then
                 IP_DST=${IPv6_DST}
                 ip netns exec ${NS3} bash -c \
                        "nc -6 -l -s ${IPv6_DST} -p 9000 > ${TMPFILE} &"
                 RET=$?
         else
                 echo "    test_gso: unknown PROTO: ${PROTO}"
	fi

I have couple of queries around it

a) why -l is being used for reading listen on IPv*_DST with -s option.
I was looking at https://www.computerhope.com/unix/nc.htm, following has 
been mentioned:
-l :  Used to specify that nc should listen for an incoming connection 
rather than initiate a connection to a
remote host. It is an error to use this option in conjunction with the 
-p, -s, or -z options.
Additionally, any timeouts specified with the -w option are ignored.

b) Even if there is requirement of -l option to use. can we provide 
timeout option also. how? as -w dont work with -l.


I am facing an issue with Linux-5.3 Kselftest where even if 
test_lwt_ip_encap.sh "exit", bpf/runner.sh is not
running next test case. It just wait until CRTL + c is pressed.
If I comment above code things work fine.


Please sugggest

--prabhakar (pk)