selftests: mptcp: info: hide 'grep: write error' warnings

mptcp_lib_get_info_value() will only print the first entry that match
the filter because of the ';q' at the end. As a consequence, the 'sed'
command could finish before the previous 'grep' one and print a 'write
error' warning because it is trying to write data to the closed pipe.

Such warnings are not interesting, they can be hidden by muting stderr
here for grep.

While at it, clearly indicate that mptcp_lib_get_info_value() will only
print the first matched entry to avoid confusions later on.

Reviewed-by: Mat Martineau <martineau@kernel.org>
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
Link: https://patch.msgid.link/20250502-net-next-mptcp-sft-inc-cover-v1-1-68eec95898fb@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

diff --git a/tools/testing/selftests/net/mptcp/mptcp_lib.sh b/tools/testing/selftests/net/mptcp/mptcp_lib.sh
index 051e289d79676c5feb9f46da67a08116548f4b47..99c87cd6e25563e220263c813223206ef6f4b311 100644 (file)
--- a/tools/testing/selftests/net/mptcp/mptcp_lib.sh
+++ b/tools/testing/selftests/net/mptcp/mptcp_lib.sh
@@ -331,12 +331,15 @@ mptcp_lib_result_print_all_tap() {
 
 # get the value of keyword $1 in the line marked by keyword $2
 mptcp_lib_get_info_value() {
-       grep "${2}" | sed -n 's/.*\('"${1}"':\)\([0-9a-f:.]*\).*$/\2/p;q'
+       grep "${2}" 2>/dev/null |
+               sed -n 's/.*\('"${1}"':\)\([0-9a-f:.]*\).*$/\2/p;q'
+               # the ';q' at the end limits to the first matched entry.
 }
 
 # $1: info name ; $2: evts_ns ; [$3: event type; [$4: addr]]
 mptcp_lib_evts_get_info() {
-       grep "${4:-}" "${2}" | mptcp_lib_get_info_value "${1}" "^type:${3:-1},"
+       grep "${4:-}" "${2}" 2>/dev/null |
+               mptcp_lib_get_info_value "${1}" "^type:${3:-1},"
 }
 
 # $1: PID