selftests: forwarding: Avoid failures to source net/lib.sh

The expression "source ../lib.sh" added to net/forwarding/lib.sh in commit
25ae948b ("selftests/net: add lib.sh") does not work for tests outside
net/forwarding which source net/forwarding/lib.sh (1). It also does not
work in some cases where only a subset of tests are exported (2).

Avoid the problems mentioned above by replacing the faulty expression with
a copy of the content from net/lib.sh which is used by files under
net/forwarding.

A more thorough solution which avoids duplicating content between
net/lib.sh and net/forwarding/lib.sh has been posted here:
https://lore.kernel.org/netdev/20231222135836.992841-1-bpoirier@nvidia.com/

The approach in the current patch is a stopgap solution to avoid submitting
large changes at the eleventh hour of this development cycle.

Example of problem 1)

tools/testing/selftests/drivers/net/bonding$ ./dev_addr_lists.sh
./net_forwarding_lib.sh: line 41: ../lib.sh: No such file or directory
TEST: bonding cleanup mode active-backup                            [ OK ]
TEST: bonding cleanup mode 802.3ad                                  [ OK ]
TEST: bonding LACPDU multicast address to slave (from bond down)    [ OK ]
TEST: bonding LACPDU multicast address to slave (from bond up)      [ OK ]

An error message is printed but since the test does not use functions from
net/lib.sh, the test results are not affected.

Example of problem 2)

tools/testing/selftests$ make install TARGETS="net/forwarding"
tools/testing/selftests$ cd kselftest_install/net/forwarding/
tools/testing/selftests/kselftest_install/net/forwarding$ ./pedit_ip.sh veth{0..3}
lib.sh: line 41: ../lib.sh: No such file or directory
TEST: ping                                                          [ OK ]
TEST: ping6                                                         [ OK ]
./pedit_ip.sh: line 135: busywait: command not found
TEST: dev veth1 ingress pedit ip src set 198.51.100.1               [FAIL]
        Expected to get 10 packets, but got .
./pedit_ip.sh: line 135: busywait: command not found
TEST: dev veth2 egress pedit ip src set 198.51.100.1                [FAIL]
        Expected to get 10 packets, but got .
./pedit_ip.sh: line 135: busywait: command not found
TEST: dev veth1 ingress pedit ip dst set 198.51.100.1               [FAIL]
        Expected to get 10 packets, but got .
./pedit_ip.sh: line 135: busywait: command not found
TEST: dev veth2 egress pedit ip dst set 198.51.100.1                [FAIL]
        Expected to get 10 packets, but got .
./pedit_ip.sh: line 135: busywait: command not found
TEST: dev veth1 ingress pedit ip6 src set 2001:db8:2::1             [FAIL]
        Expected to get 10 packets, but got .
./pedit_ip.sh: line 135: busywait: command not found
TEST: dev veth2 egress pedit ip6 src set 2001:db8:2::1              [FAIL]
        Expected to get 10 packets, but got .
./pedit_ip.sh: line 135: busywait: command not found
TEST: dev veth1 ingress pedit ip6 dst set 2001:db8:2::1             [FAIL]
        Expected to get 10 packets, but got .
./pedit_ip.sh: line 135: busywait: command not found
TEST: dev veth2 egress pedit ip6 dst set 2001:db8:2::1              [FAIL]
        Expected to get 10 packets, but got .

In this case, the test results are affected.

Fixes: 25ae948b ("selftests/net: add lib.sh")
Suggested-by: Ido Schimmel <idosch@nvidia.com>
Suggested-by: Petr Machata <petrm@nvidia.com>
Reviewed-by: Ido Schimmel <idosch@nvidia.com>
Tested-by: Petr Machata <petrm@nvidia.com>
Signed-off-by: Benjamin Poirier <bpoirier@nvidia.com>
Reviewed-by: Hangbin Liu <liuhangbin@gmail.com>
Link: https://lore.kernel.org/r/20240104141109.100672-1-bpoirier@nvidia.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>

tools/testing/selftests/net/forwarding/lib.sh

@@ -38,7 +38,32 @@ if [[ -f $relative_path/forwarding.config ]]; then
 	source "$relative_path/forwarding.config"
 fi
 
-source ../lib.sh
+# Kselftest framework requirement - SKIP code is 4.
+ksft_skip=4
+
+busywait()
+{
+	local timeout=$1; shift
+
+	local start_time="$(date -u +%s%3N)"
+	while true
+	do
+		local out
+		out=$("$@")
+		local ret=$?
+		if ((!ret)); then
+			echo -n "$out"
+			return 0
+		fi
+
+		local current_time="$(date -u +%s%3N)"
+		if ((current_time - start_time > timeout)); then
+			echo -n "$out"
+			return 1
+		fi
+	done
+}
+
 ##############################################################################
 # Sanity checks