lightningd: clean up pidfile test, crashlog.

1. Now checking the pid file really does precede touching the db and
   starting plugins, which is far safer.
2. Crashlog is now activated just after daemon parent release, and just
   before the main loop, which means no "crash" on startup if we call fatal().

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

lightningd/lightningd.c

@@ -538,12 +538,14 @@ static void complete_daemonize(struct lightningd *ld)
  * file-lock a pidfile.  This not only prevents accidentally running multiple
  * daemons on the same database at once, but lets nosy sysadmins see what pid
  * the currently-running daemon is supposed to be. */
-static int pidfile_create(const struct lightningd *ld)
+static void pidfile_create(const struct lightningd *ld)
 {
 	int pid_fd;
+	char *pid;
 
-	/* Create PID file */
-	pid_fd = open(ld->pidfile, O_WRONLY|O_CREAT, 0640);
+	/* Create PID file: relative to .config dir unless absolute. */
+	pid_fd = open(path_join(tmpctx, ld->config_dir, ld->pidfile),
+		      O_WRONLY|O_CREAT, 0640);
 	if (pid_fd < 0)
 		err(1, "Failed to open PID file");
 
@@ -554,15 +556,6 @@ static int pidfile_create(const struct lightningd *ld)
 
 	/*~ As closing the file will remove the lock, we need to keep it open;
 	 * the OS will close it implicitly when we exit for any reason. */
-	return pid_fd;
-}
-
-/*~ Writing the pid into the lockfile provides a useful clue to users as to
- * what created it; however, we can't do that until we've got a stable process
- * id, and if --daemon is specified, that's quite late. */
-static void pidfile_write(const struct lightningd *ld, int pid_fd)
-{
-	char *pid;
 
 	/*~ Note that tal_fmt() is what asprintf() dreams of being. */
 	pid = tal_fmt(tmpctx, "%d\n", getpid());
@@ -635,7 +628,7 @@ int main(int argc, char *argv[])
 {
 	struct lightningd *ld;
 	u32 min_blockheight, max_blockheight;
-	int connectd_gossipd_fd, pid_fd;
+	int connectd_gossipd_fd;
 	int stop_fd;
 	struct timers *timers;
 	const char *stop_response;
@@ -675,9 +668,14 @@ int main(int argc, char *argv[])
 	/*~ Handle early options, but don't move to --lightning-dir
 	 *  just yet. Plugins may add new options, which is why we are
 	 *  splitting between early args (including --plugin
-	 *  registration) and non-early opts. */
+	 *  registration) and non-early opts.  This also forks if they
+	 *  say --daemonize. */
 	handle_early_opts(ld, argc, argv);
 
+	/*~ Now create the PID file: this errors out if there's already a
+	 * daemon running, so we call before doing almost anything else. */
+	pidfile_create(ld);
+
 	/*~ Initialize all the plugins we just registered, so they can
 	 *  do their thing and tell us about themselves (including
 	 *  options registration). */
@@ -775,10 +773,6 @@ int main(int argc, char *argv[])
 	load_channels_from_wallet(ld);
 	db_commit_transaction(ld->wallet->db);
 
-	/*~ Now create the PID file: this errors out if there's already a
-	 * daemon running, so we call before trying to create an RPC socket. */
-	pid_fd = pidfile_create(ld);
-
 	/*~ Create RPC socket: now lightning-cli can send us JSON RPC commands
 	 *  over a UNIX domain socket specified by `ld->rpc_filename`. */
 	jsonrpc_listen(ld->jsonrpc, ld);
@@ -787,14 +781,6 @@ int main(int argc, char *argv[])
 	 * can start talking to us. */
 	plugins_config(ld->plugins);
 
-	/*~ Setting this (global) activates the crash log: we don't usually need
-	 * a backtrace if we fail during startup.  We do this before daemonize,
-	 * in case that runs into trouble. */
-	crashlog = ld->log;
-
-	/*~ We have to do this after daemonize, since that changes our pid! */
-	pidfile_write(ld, pid_fd);
-
 	/*~ Activate connect daemon.  Needs to be after the initialization of
 	 * chaintopology, otherwise peers may connect and ask for
 	 * uninitialized data. */
@@ -840,6 +826,10 @@ int main(int argc, char *argv[])
 	if (ld->daemon_parent_fd != -1)
 		complete_daemonize(ld);
 
+	/*~ Setting this (global) activates the crash log: we don't usually need
+	 * a backtrace if we fail during startup. */
+	crashlog = ld->log;
+
 	/*~ The root of every backtrace (almost).  This is our main event
 	 *  loop. */
 	void *io_loop_ret = io_loop_with_timers(ld);