scripts: get debug info for bug reports

This is a simple script that is here to get debug info. It will be
helpful to get more details in case of issues with MPTCP in general,
not specific to mptcpd or mptcpize then.

The script is basic, supporting /bin/sh with a minimum of dependences.

It should be used with '--collect' or '--reproduce', as shown by the
help menu.

Please note that a lot of efforts have been done recently to improve the
documentation on mptcp.dev website, on the kernel side, and on IPRoute
side. Thanks to that, this script can be small, focussing on this small
set of commands for the moment. It can always be improved later on.

The idea is to place it here in mptcpd, to have it somewhere, and
ideally already installed on some machines, in /usr/libexec dir, ready
to be used without having to install it.

Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>

scripts/Makefile.am

@@ -3,3 +3,5 @@
 ## Copyright (c) 2018, 2019, Intel Corporation
 
 dist_noinst_SCRIPTS = check-permissions
+
+dist_libexec_SCRIPTS = mptcp-get-debug

scripts/mptcp-get-debug

@@ -0,0 +1,129 @@
+#! /bin/sh
+# SPDX-License-Identifier: BSD-3-Clause
+#
+# Copyright (c) 2024, Matthieu Baerts
+
+SCRIPT="$(basename "${0}")"
+VERSION="1"
+PID_IP=
+
+EQ="========================================"
+
+title() {
+    printf "\n%s\n%s\n%s\n" "${EQ}" "${*}" "${EQ}"
+}
+
+stdout() {
+    printf "\n%s\n" "${*}"
+}
+
+stderr() {
+    stdout "${@}" >&2
+}
+
+cmd() {
+    title "${*}"
+    "${@}" 2>&1
+}
+
+start_ip_mptcp_monitor() {
+    title "ip mptcp monitor: start"
+    ip mptcp monitor 2>&1 &  # not using cmd to get the right PID
+    PID_IP=$!
+
+    sleep 0.1 2>/dev/null || sleep 1
+
+    for _ in $(seq 20); do
+        out="$(ss -f netlink -H "src = rtnl:${PID_IP}" 2>/dev/null)" || break
+        [ "$(echo "${out}" | wc -l)" != 0 ] && return 0
+
+        sleep 0.1 2>/dev/null || break
+    done
+
+    if [ ! -d "/proc/${PID_IP}" ]; then
+        stdout "ip monitor has been killed"
+        return 1
+    fi
+}
+
+stop_ip_mptcp_monitor() {
+    title "ip mptcp monitor: stop"
+
+    if [ -n "${PID_IP}" ] && [ -d "/proc/${PID_IP}" ]; then
+        kill "${PID_IP}"
+    fi
+}
+
+collect_data_pre() {
+    stdout "${SCRIPT}: version ${VERSION}"
+
+    if [ "$(id -u)" != 0 ]; then
+        stderr "This script is not executed as root, not all info can be collected."
+        stderr "Press Enter to continue, Ctrl+C to stop"
+        read -r _
+    fi
+
+    cmd sysctl net.mptcp
+    cmd ip mptcp endpoint show
+    cmd ip mptcp limits show
+}
+
+collect_data_post() {
+    cmd ss -ManiH
+    cmd nstat
+}
+
+collect_data() {
+    collect_data_pre
+    collect_data_post
+}
+
+collect_data_repro() {
+    collect_data_pre
+
+    cmd ss -ManiH
+    nstat -n 2>&1
+    start_ip_mptcp_monitor
+
+    stderr "Please reproduce the issue now, then press the Enter key when it is done."
+    read -r _
+
+    collect_data_post
+    stop_ip_mptcp_monitor
+}
+
+version() {
+    printf "%s: version %s\n" "${SCRIPT}" ${VERSION}
+}
+
+usage() {
+    version
+    printf "\n"
+    printf "  -c | --collect      Collect info and exit.\n"
+    printf "  -r | --reproduce    Collect info, start monitor, wait for user and exit.\n"
+    printf "  -h | --help         Show this and exit.\n"
+    printf "  -v | --version      Show the version and exit.\n"
+    printf "\n"
+    printf "Please check https://mptcp.dev website for more info.\n"
+}
+
+case "${1}" in
+    "-c" | "--collect")
+        collect_data
+        ;;
+    "-r" | "--reproduce")
+        collect_data_repro
+        ;;
+    "-h" | "--help")
+        usage
+        ;;
+    "-v" | "--version")
+        version
+        ;;
+    *)
+        usage >&2
+        exit 1
+        ;;
+esac
+
+exit 0