Change default behavior, allow kernel logs to console

A Linux system booted with the kernel command line option 'quiet' only
logs error (and above) severity messages to the console.  For embedded
systems, which is the primary target for Finit, this is what you want
to see.

Hence, and after careful consideration, this patch changes the default
behavior of Finit to allow kernel logs to the console.  A build-time
configure flags, --disable-kernel-logging, has been added to restore
legacy behavior.

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

configure.ac

@@ -71,6 +71,10 @@ AC_ARG_ENABLE(redirect,
         AS_HELP_STRING([--disable-redirect], [Disable redirection of service output to /dev/null]),,[
 	enable_redirect=yes])
 
+AC_ARG_ENABLE(kernel_logging,
+        AS_HELP_STRING([--disable-kernel-logging], [Disable kernel logging to console (use 'quiet' instead!]),,[
+	enable_kernel_logging=yes])
+
 AC_ARG_ENABLE(logrotate,
         AS_HELP_STRING([--disable-logrotate], [Disable built-in rotation of /var/log/wtmp]),,[
 	enable_logrotate=yes])
@@ -181,6 +185,9 @@ AS_IF([test "x$enable_auto_reload" = "xyes"], [
 AS_IF([test "x$enable_kernel_cmdline" = "xyes"], [
         AC_DEFINE(KERNEL_CMDLINE, 1, [Dumpster diving after init args from /proc/cmdline])])
 
+AS_IF([test "x$enable_kernel_logging" = "xyes"], [
+        AC_DEFINE(KERNEL_LOGGING, 1, [Keep kernel warn/err logs to console])])
+
 AS_IF([test "x$enable_fastboot" = "xyes"], [
 	AC_DEFINE(FAST_BOOT, 1, [Skip fsck check on filesystems listed in /etc/fstab])])
 
@@ -382,6 +389,8 @@ Optional features:
   Built-in sulogin......: $with_sulogin $sulogin
   Built-in watchdogd....: $with_watchdog $watchdog
   Built-in logrotate....: $enable_logrotate
+  Parse kernel cmdline..: $enable_kernel_cmdline
+  Keep kernel logging...: $enable_kernel_logging
   Skip fsck check.......: $enable_fastboot
   Run fsck fix mode.....: $enable_fsckfix
   Redirect output.......: $enable_redirect

src/finit.c

@@ -87,14 +87,22 @@ svc_t *wdog     = NULL;		/* No watchdog by default */
  */
 static void banner(void)
 {
+#ifndef KERNEL_LOGGING
 	/*
 	 * Silence kernel logs, assuming users have sysklogd or
-	 * similar enabled to start emptying /dev/kmsg, but for
-	 * our progress we want to own the console.
+	 * similar enabled to start emptying /dev/kmsg.
+	 *
+	 * Instead of using `configure --disable-kernel-logging`, we
+	 * recommend adjusting the kernel log level in the kernel's
+	 * menuconfig, or using sysctl kernel.printk, or setting the
+	 * desired log level, on the kernel cmdline, e.g. 'quiet'.
+	 *
+	 * By default KERNEL_LOGGING is enabled so you can see any
+	 * warnings/errors or higher on your system console.
 	 */
 	if (!debug && !kerndebug)
 		klogctl(6, NULL, 0);
-
+#endif
 	/*
 	 * First level hooks, if you want to run here, you're
 	 * pretty much on your own.  Nothing's up yet ...