test: add test for the new memory pressure unit file settings, and that they work

test/TEST-79-MEMPRESS/Makefile

@@ -0,0 +1 @@
+../TEST-01-BASIC/Makefile

test/TEST-79-MEMPRESS/test.sh

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+#!/usr/bin/env bash
+# SPDX-License-Identifier: LGPL-2.1-or-later
+set -e
+
+TEST_DESCRIPTION="Test Memory Pressure handling"
+# Ignore gcov complaints caused by DynamicUser=true
+IGNORE_MISSING_COVERAGE=yes
+
+# shellcheck source=test/test-functions
+. "$TEST_BASE_DIR/test-functions"
+
+test_append_files() {
+    image_install base64
+}
+
+do_test "$@"

test/units/testsuite-79.service

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+# SPDX-License-Identifier: LGPL-2.1-or-later
+[Unit]
+Description=TEST-79-MEMPRESS
+
+[Service]
+Type=oneshot
+ExecStart=/usr/lib/systemd/tests/testdata/units/%N.sh
+MemoryAccounting=1

test/units/testsuite-79.sh

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+#!/usr/bin/env bash
+# SPDX-License-Identifier: LGPL-2.1-or-later
+set -ex
+set -o pipefail
+
+# We not just test if the file exists, but try to read from it, since if
+# CONFIG_PSI_DEFAULT_DISABLED is set in the kernel the file will exist and can
+# be opened, but any read()s will fail with EOPNOTSUPP, which we want to
+# detect.
+if ! cat /proc/pressure/memory >/dev/null ; then
+    echo "kernel too old, has no PSI." >&2
+    echo OK >/testok
+    exit 0
+fi
+
+systemd-analyze log-level debug
+
+CGROUP=/sys/fs/cgroup/"$(systemctl show testsuite-79.service -P ControlGroup)"
+test -d "$CGROUP"
+
+if ! test -f "$CGROUP"/memory.pressure ; then
+    echo "No memory accounting/PSI delegated via cgroup, can't test." >&2
+    echo OK >/testok
+    exit 0
+fi
+
+UNIT="test-mempress-$RANDOM.service"
+SCRIPT="/run/bin/mempress-$RANDOM.sh"
+
+mkdir -p "/run/bin"
+
+cat >"$SCRIPT" <<'EOF'
+#!/bin/bash
+
+set -ex
+
+export
+id
+
+test -n "$MEMORY_PRESSURE_WATCH"
+test "$MEMORY_PRESSURE_WATCH" != /dev/null
+test -w "$MEMORY_PRESSURE_WATCH"
+
+ls -al "$MEMORY_PRESSURE_WATCH"
+
+EXPECTED="$(echo -n -e "some 123000 1000000\x00" | base64)"
+
+test "$EXPECTED" = "$MEMORY_PRESSURE_WRITE"
+
+EOF
+
+chmod +x "$SCRIPT"
+
+systemd-run -u "$UNIT" -p Type=exec -p DynamicUser=1 -p MemoryPressureWatch=on -p MemoryPressureThresholdSec=123ms --wait "$SCRIPT"
+
+rm "$SCRIPT"
+
+rmdir /run/bin ||:
+
+systemd-analyze log-level info
+echo OK >/testok
+
+exit 0