selftests: mptcp: diag: use mptcp_lib_get_info_value

JIRA: https://issues.redhat.com/browse/RHEL-115576
Upstream Status: net-next.git commit ce72fea

commit ce72fea
Author: Geliang Tang <geliang@kernel.org>
Date:   Mon Apr 21 19:07:14 2025 +0200

    selftests: mptcp: diag: use mptcp_lib_get_info_value

    When running diag.sh in a loop, chk_dump_one will report the following
    "grep: write error":

     13 ....chk 2 cestab                                  [ OK ]
     grep: write error
     14 ....chk dump_one                                  [ OK ]
     15 ....chk 2->0 msk in use after flush               [ OK ]
     16 ....chk 2->0 cestab after flush                   [ OK ]

    This error is caused by a broken pipe. When the output of 'ss' is processed
    by grep, 'head -n 1' will exit immediately after getting the first line,
    causing the subsequent pipe to close. At this time, if 'grep' is still
    trying to write data to the closed pipe, it will trigger a SIGPIPE signal,
    causing a write error.

    One solution is not to use this problematic "head -n 1" command, but to use
    mptcp_lib_get_info_value() helper defined in mptcp_lib.sh to get the value
    of 'token'.

    Fixes: ba24001 ("selftests: mptcp: add a test for mptcp_diag_dump_one")
    Signed-off-by: Geliang Tang <tanggeliang@kylinos.cn>
    Reviewed-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
    Tested-by: Gang Yan <yangang@kylinos.cn>
    Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
    Link: https://patch.msgid.link/20250421-net-mptcp-pm-defer-freeing-v1-2-e731dc6e86b9@kernel.org
    Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Signed-off-by: Davide Caratti <dcaratti@redhat.com>

Author: dcaratti

tools/testing/selftests/net/mptcp/diag.sh

@@ -206,9 +206,8 @@ chk_dump_one()
 	local token
 	local msg
 
-	ss_token="$(ss -inmHMN $ns | grep 'token:' |\
-		    head -n 1 |\
-		    sed 's/.*token:\([0-9a-f]*\).*/\1/')"
+	ss_token="$(ss -inmHMN $ns |
+		    mptcp_lib_get_info_value "token" "token")"
 
 	token="$(ip netns exec $ns ./mptcp_diag -t $ss_token |\
 		 awk -F':[ \t]+' '/^token/ {print $2}')"