sched: Only setting CPUSchedulingPriority=rr doesn't work

A service that only sets the scheduling policy to round-robin
fails to be started. This is because the cpu_sched_priority is
initialized to 0 and is not adjusted when the policy is changed.

Clamp the cpu_sched_priority when the scheduler policy is set. Use
the current policy to validate the new priority.

Change the manual page to state that the given range only applies
to the real-time scheduling policies.

Add a testcase that verifies this change:

$ make test-sched-prio; ./test-sched-prio
[test/sched_idle_bad.service:6] CPU scheduling priority is out of range, ignoring: 1
[test/sched_rr_bad.service:7] CPU scheduling priority is out of range, ignoring: 0
[test/sched_rr_bad.service:8] CPU scheduling priority is out of range, ignoring: 100

1 files changed, 86 insertions, 0 deletions

diff --git a/src/test/test-sched-prio.c b/src/test/test-sched-prio.c
new file mode 100644
index 0000000000..29235e8347
--- /dev/null
+++ b/src/test/test-sched-prio.c
@@ -0,0 +1,86 @@
+/*-*- Mode: C; c-basic-offset: 8; indent-tabs-mode: nil -*-*/
+
+/***
+  This file is part of systemd.
+
+  Copyright 2012 Holger Hans Peter Freyther
+
+  systemd is free software; you can redistribute it and/or modify it
+  under the terms of the GNU Lesser General Public License as published by
+  the Free Software Foundation; either version 2.1 of the License, or
+  (at your option) any later version.
+
+  systemd is distributed in the hope that it will be useful, but
+  WITHOUT ANY WARRANTY; without even the implied warranty of
+  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+  Lesser General Public License for more details.
+
+  You should have received a copy of the GNU Lesser General Public License
+  along with systemd; If not, see <http://www.gnu.org/licenses/>.
+***/
+
+#include <sched.h>
+
+#include "manager.h"
+
+
+int main(int argc, char *argv[]) {
+        Manager *m;
+        Unit *idle_ok, *idle_bad, *rr_ok, *rr_bad, *rr_sched;
+        Service *ser;
+        FILE *serial = NULL;
+        FDSet *fdset = NULL;
+
+        /* prepare the test */
+        assert_se(set_unit_path(TEST_DIR) >= 0);
+        assert_se(manager_new(SYSTEMD_SYSTEM, &m) >= 0);
+        assert_se(manager_startup(m, serial, fdset) >= 0);
+
+        /* load idle ok */
+        assert_se(manager_load_unit(m, "sched_idle_ok.service", NULL, NULL, &idle_ok) >= 0);
+        assert_se(idle_ok->load_state == UNIT_LOADED);
+        ser = SERVICE(idle_ok);
+        assert_se(ser->exec_context.cpu_sched_policy == SCHED_OTHER);
+        assert_se(ser->exec_context.cpu_sched_priority == 0);
+
+        /*
+         * load idle bad. This should print a warning but we have no way to look at it.
+         */
+        assert_se(manager_load_unit(m, "sched_idle_bad.service", NULL, NULL, &idle_bad) >= 0);
+        assert_se(idle_bad->load_state == UNIT_LOADED);
+        ser = SERVICE(idle_ok);
+        assert_se(ser->exec_context.cpu_sched_policy == SCHED_OTHER);
+        assert_se(ser->exec_context.cpu_sched_priority == 0);
+
+        /*
+         * load rr ok.
+         * Test that the default priority is moving from 0 to 1.
+         */
+        assert_se(manager_load_unit(m, "sched_rr_ok.service", NULL, NULL, &rr_ok) >= 0);
+        assert_se(rr_ok->load_state == UNIT_LOADED);
+        ser = SERVICE(rr_ok);
+        assert_se(ser->exec_context.cpu_sched_policy == SCHED_RR);
+        assert_se(ser->exec_context.cpu_sched_priority == 1);
+
+        /*
+         * load rr bad.
+         * Test that the value of 0 and 100 is ignored.
+         */
+        assert_se(manager_load_unit(m, "sched_rr_bad.service", NULL, NULL, &rr_bad) >= 0);
+        assert_se(rr_bad->load_state == UNIT_LOADED);
+        ser = SERVICE(rr_bad);
+        assert_se(ser->exec_context.cpu_sched_policy == SCHED_RR);
+        assert_se(ser->exec_context.cpu_sched_priority == 1);
+
+        /*
+         * load rr change.
+         * Test that anything between 1 and 99 can be set.
+         */
+        assert_se(manager_load_unit(m, "sched_rr_change.service", NULL, NULL, &rr_sched) >= 0);
+        assert_se(rr_sched->load_state == UNIT_LOADED);
+        ser = SERVICE(rr_sched);
+        assert_se(ser->exec_context.cpu_sched_policy == SCHED_RR);
+        assert_se(ser->exec_context.cpu_sched_priority == 99);
+
+        return 0;
+}