From 2d231a97af31f9d4f5276944e3632b4bb6e25f97 Mon Sep 17 00:00:00 2001
From: "K. Lange" <klange@toaruos.org>
Date: Tue, 14 Aug 2018 14:45:30 +0900
Subject: [PATCH] Cleanup init

---
 apps/init.c | 80 +++++++++++++++++++++++++++++++++++++++++------------
 1 file changed, 63 insertions(+), 17 deletions(-)

diff --git a/apps/init.c b/apps/init.c
index 54700242..765386ee 100644
--- a/apps/init.c
+++ b/apps/init.c
@@ -1,3 +1,35 @@
+/* vim: ts=4 sw=4 noexpandtab
+ * This file is part of ToaruOS and is released under the terms
+ * of the NCSA / University of Illinois License - see LICENSE.md
+ * Copyright (C) 2018 K. Lange
+ *
+ * init - First process.
+ *
+ * `init` calls startup scripts and then waits for them to complete.
+ * It also waits for orphaned proceses so they can be collected.
+ *
+ * `init` itself is statically-linked, so minimizing libc dependencies
+ * is worthwhile as it reduces to the total size of init itself, which
+ * remains in memory throughout the entire lifetime of the OS.
+ *
+ * Startup scripts for init are stored in /etc/startup.d and are run
+ * in sorted alphabetical order. It is generally recommended that these
+ * startup scripts be named with numbers at the front to ensure easy
+ * ordering. This system of running a set of scripts on startup is
+ * somewhat similar to how sysvinit worked, but no claims of
+ * compatibility are made.
+ *
+ * Startup scripts can be any executable binary. Shell scripts are
+ * generally used to allow easy editing, but you could also use
+ * a binary (even a dynamically linked one) as a startup script.
+ * `init` will wait for each startup script (that is, it will wait for
+ * the original process it started to exit) before running the next one.
+ * So if you wish to run daemons, be sure to fork them off and then
+ * exit so that the rest of the startup process can continue.
+ *
+ * When the last startup script finishes, `init` will reboot the system.
+ */
+
 #include <dirent.h>
 #include <errno.h>
 #include <stdio.h>
@@ -10,43 +42,56 @@
 
 #define INITD_PATH "/etc/startup.d"
 
+/* Initialize fd 0, 1, 2 */
 void set_console(void) {
+	/* default to /dev/ttyS0 (serial COM1) */
 	int _stdin  = syscall_open("/dev/ttyS0", 0, 0);
-	int _stdout = syscall_open("/dev/ttyS0", 1, 0);
-	int _stderr = syscall_open("/dev/ttyS0", 1, 0);
-
-	if (_stdout < 0) {
-		_stdout = syscall_open("/dev/null", 1, 0);
-		_stderr = syscall_open("/dev/null", 1, 0);
+	if (_stdin < 0) {
+		/* if /dev/ttyS0 failed to open, fall back to /dev/null */
+		syscall_open("/dev/null", 0, 0);
+		syscall_open("/dev/null", 1, 0);
+		syscall_open("/dev/null", 1, 0);
+	} else {
+		/* otherwise also use /dev/ttyS0 for stdout, stderr */
+		syscall_open("/dev/ttyS0", 1, 0);
+		syscall_open("/dev/ttyS0", 1, 0);
 	}
-
-	(void)_stderr;
-	(void)_stdin;
 }
 
+/* Run a startup script and wait for it to finish */
 int start_options(char * args[]) {
+
+	/* Fork child to run script */
 	int cpid = syscall_fork();
+
+	/* Child process... */
 	if (!cpid) {
-		char * _envp[] = {
-			"LD_LIBRARY_PATH=/lib:/usr/lib",
-			"PATH=/bin:/usr/bin",
-			"USER=root",
-			"HOME=/home/root",
-			NULL,
-		};
-		syscall_execve(args[0], args, _envp);
+		/* Pass environment from init to child */
+		syscall_execve(args[0], args, environ);
+		/* exec failed, exit this subprocess */
 		syscall_exit(0);
 	}
 
+	/* Wait for the child process to finish */
 	int pid = 0;
 	do {
+		/*
+		 * Wait, ignoring kernel threads
+		 * (which also end up as children to init)
+		 */
 		pid = waitpid(-1, NULL, WNOKERN);
+
 		if (pid == -1 && errno == ECHILD) {
+			/* There are no more children */
 			break;
 		}
+
 		if (pid == cpid) {
+			/* The child process finished */
 			break;
 		}
+
+		/* Continue while no error (or error was "interrupted") */
 	} while ((pid > 0) || (pid == -1 && errno == EINTR));
 
 	return cpid;
@@ -95,6 +140,7 @@ int main(int argc, char * argv[]) {
 		}
 	}
 
+	/* Self-explanatory */
 	syscall_reboot();
 	return 0;
 }