test: regression for stale pidfile cleanup after unclean exit

Cover the scenario fixed in "service: clean stale pidfile after
unclean daemon exit": a daemon with a pid:!/path config dies via
SIGKILL, leaving its pidfile behind, and the next instance must
still come up.

Add a 'serv -x' flag (refuse to start when the pidfile already
exists, dbus-style) so the test actually exercises the cleanup --
without it, plain 'serv' would happily overwrite the file and the
test would pass with or without the fix.

Signed-off-by: Joachim Wiberg <troglobit@gmail.com>

test/Makefile.am

@@ -41,6 +41,7 @@ EXTRA_DIST		+= global-envs.sh
 EXTRA_DIST		+= initctl-status-subset.sh
 EXTRA_DIST		+= notify.sh
 EXTRA_DIST		+= pidfile.sh
+EXTRA_DIST		+= stale-pidfile.sh
 EXTRA_DIST		+= pre-post-serv.sh
 EXTRA_DIST		+= pre-fail.sh
 EXTRA_DIST		+= process-depends.sh
@@ -84,6 +85,7 @@ TESTS			+= global-envs.sh
 TESTS			+= initctl-status-subset.sh
 TESTS			+= notify.sh
 TESTS			+= pidfile.sh
+TESTS			+= stale-pidfile.sh
 TESTS			+= pre-post-serv.sh
 TESTS			+= pre-fail.sh
 TESTS			+= process-depends.sh

test/src/serv.c

@@ -34,6 +34,7 @@ volatile sig_atomic_t reloading = 1;
 volatile sig_atomic_t running   = 1;
 static char *ident = PROGNM;
 static char fn[80];
+static int  exclusive = 0;	/* -x: refuse to start if pidfile exists (dbus-style) */
 
 static void verify_env(char *arg)
 {
@@ -122,7 +123,7 @@ static void writefn(char *fn, int val)
 
 static int checkfn(char *fn)
 {
-	return !access(fn, R_OK);
+	return !access(fn, F_OK);
 }
 
 static void mine(char *fn)
@@ -133,12 +134,18 @@ static void mine(char *fn)
 
 static void pidfile(char *pidfn)
 {
+	static int once = 0;
+
 	if (!pidfn) {
 		if (fn[0] == 0)
 			snprintf(fn, sizeof(fn), "%s%s.pid", _PATH_VARRUN, ident);
 		pidfn = fn;
 	}
 
+	if (exclusive && !once && checkfn(pidfn))
+		errx(EX_SOFTWARE, "PID file %s exists, refusing to start", pidfn);
+	once = 1;
+
 	if (!checkfn(pidfn)) {
 		pid_t pid;
 
@@ -148,7 +155,7 @@ static void pidfile(char *pidfn)
 		atexit(cleanup);
 	} else {
 		inf("Touching PID file %s", pidfn);
-		utimensat(0, fn, NULL, 0);
+		utimensat(AT_FDCWD, pidfn, NULL, 0);
 	}
 }
 
@@ -182,6 +189,7 @@ static int usage(int rc)
 		" -p       Create PID file despite running in foreground\n"
 		" -P FILE  Create PID file using FILE\n"
 		" -r SVC   Call initctl to restart service SVC (self)\n"
+		" -x       Refuse to start if PID file already exists (dbus-style)\n"
 		"\n"
 		"By default this program daemonizes itself to the background, and,\n"
 		"when it's done setting up its signal handler(s), creates a PID file\n"
@@ -212,7 +220,7 @@ int main(int argc, char *argv[])
 	char cmd[80];
 	int c;
 
-	while ((c = getopt(argc, argv, "cCe:E:f:F:hi:nN:pP:r:")) != EOF) {
+	while ((c = getopt(argc, argv, "cCe:E:f:F:hi:nN:pP:r:x")) != EOF) {
 		switch (c) {
 		case 'c':
 			do_crash = 1;
@@ -249,12 +257,17 @@ int main(int argc, char *argv[])
 			break;
 		case 'P':
 			pidfn = optarg;
+			if ((size_t)snprintf(fn, sizeof(fn), "%s", optarg) >= sizeof(fn))
+				errx(EX_USAGE, "-P path too long (max %zu)", sizeof(fn) - 1);
 			do_pidfile++;
 			break;
 		case 'r':
 			snprintf(cmd, sizeof(cmd), "initctl restart %s", optarg);
 			do_restart = 1;
 			break;
+		case 'x':
+			exclusive = 1;
+			break;
 		default:
 			return usage(1);
 		}

test/stale-pidfile.sh

@@ -0,0 +1,38 @@
+#!/bin/sh
+# Regression: Finit must remove a daemon-owned (pid:!) stale pidfile
+# left behind by an unclean exit (SIGKILL), so the next instance can
+# start.  Simulates the dbus-daemon pattern: 'serv -x' refuses to
+# start if its pidfile already exists.
+
+set -eu
+
+TEST_DIR=$(dirname "$0")
+PIDFN="/run/serv.pid"
+
+test_teardown()
+{
+    say "Running test teardown."
+    run "rm -f $FINIT_CONF $PIDFN"
+}
+
+# shellcheck source=/dev/null
+. "$TEST_DIR/lib/setup.sh"
+
+say "Add service stanza '$FINIT_CONF' with pid:!$PIDFN"
+run "echo 'service pid:!$PIDFN serv -np -P $PIDFN -x' > $FINIT_CONF"
+run "initctl reload"
+
+retry "assert_num_children 1 serv"
+assert_is_pidfile "serv" "$PIDFN"
+
+PID=$(texec cat "$PIDFN")
+say "SIGKILL serv ($PID) -- leaves stale pidfile"
+run "kill -9 $PID"
+
+# Without the fix, 'serv -x' refuses to start on each retry until
+# Finit hits restart_max and marks the service crashed.  With the fix
+# Finit removes the stale pidfile and the next instance comes up.
+retry "assert_pidiff serv $PID"
+retry "assert_num_children 1 serv"
+
+sep