BUG/MINOR: startup: fix pidfile creation

Pidfile should be created at the latest initialization stage, when we are
sure, that process is able to start successfully, otherwise PID value, written
in this file is no longer valid.

So, for the standalone mode, let's move the block, which opens the pidfile and
let's put it just before applying "chroot". In master-worker mode, master
doesn't perform chroot. So it creates the pidfile, only when the "READY"
message from the newly forked worker is received.

This should be backported only in 3.1

src/cli.c

@@ -2526,6 +2526,14 @@ static int _send_status(char **args, char *payload, struct appctx *appctx, void
 			kill(proc->pid, oldpids_sig);
 		}
 	}
+
+	/* At this point we are sure, that newly forked worker is started,
+	 * so we can write our PID in a pidfile, if provided. Master doesn't
+	 * perform chroot.
+	 */
+	if (global.pidfile != NULL)
+		handle_pidfile();
+
 	load_status = 1;
 	ha_notice("Loading success.\n");
 

src/haproxy.c

@@ -3370,10 +3370,6 @@ int main(int argc, char **argv)
 	if ((getenv("HAPROXY_MWORKER_REEXEC") == NULL) && (global.mode & MODE_DAEMON))
 		apply_daemon_mode();
 
-	/* Open pid file before the chroot */
-	if ((global.mode & MODE_DAEMON || global.mode & MODE_MWORKER) && global.pidfile != NULL)
-		handle_pidfile();
-
 	/* Master-worker and program forks */
 	if (global.mode & MODE_MWORKER) {
 		/* fork and run binary from command keyword in program section */
@@ -3528,6 +3524,15 @@ int main(int argc, char **argv)
 		}
 	}
 
+	/* Open PID file before the chroot. In master-worker mode, it's master
+	 * who will create the pidfile, see _send_status().
+	 */
+	if (!(global.mode & MODE_MWORKER)) {
+		if (global.mode & MODE_DAEMON && (global.pidfile != NULL)) {
+			handle_pidfile();
+		}
+	}
+
 	/* Must chroot and setgid/setuid in the children */
 	/* chroot if needed */
 	if (global.chroot != NULL) {