raid: make RAID autodetect default a KConfig option

RAID autodetect has the side effect of requiring synchronisation
of all device drivers, which can make the boot several seconds longer
(I've measured 7 on one of my laptops).... even for systems that don't
have RAID setup for the root filesystem (the only FS where this matters).

This patch makes the default for autodetect a config option; either way
the user can always override via the kernel command line.

Signed-off-by: Arjan van de Ven <arjan@linux.intel.com>
Acked-by: NeilBrown <neilb@suse.de>

drivers/md/Kconfig

@@ -30,6 +30,20 @@ config BLK_DEV_MD
 
 	  If unsure, say N.
 
+config MD_AUTODETECT
+	bool "Autodetect RAID arrays during kernel boot"
+	depends on BLK_DEV_MD
+	default y
+	---help---
+	  If you say Y here, then the kernel will try to autodetect raid
+	  arrays as part of its boot process. 
+
+	  If you don't use raid and say Y, this autodetection can cause 
+	  a several-second delay in the boot time due to various
+	  synchronisation steps that are part of this step.
+
+	  If unsure, say Y.
+
 config MD_LINEAR
 	tristate "Linear (append) mode"
 	depends on BLK_DEV_MD

init/do_mounts_md.c

@@ -12,7 +12,12 @@
  * The code for that is here.
  */
 
-static int __initdata raid_noautodetect, raid_autopart;
+#ifdef CONFIG_MD_AUTODETECT
+static int __initdata raid_noautodetect;
+#else
+static int __initdata raid_noautodetect=1;
+#endif
+static int __initdata raid_autopart;
 
 static struct {
 	int minor;
@@ -252,6 +257,8 @@ static int __init raid_setup(char *str)
 
 		if (!strncmp(str, "noautodetect", wlen))
 			raid_noautodetect = 1;
+		if (!strncmp(str, "autodetect", wlen))
+			raid_noautodetect = 0;
 		if (strncmp(str, "partitionable", wlen)==0)
 			raid_autopart = 1;
 		if (strncmp(str, "part", wlen)==0)
@@ -288,7 +295,7 @@ void __init md_run_setup(void)
 	create_dev("/dev/md0", MKDEV(MD_MAJOR, 0));
 
 	if (raid_noautodetect)
-		printk(KERN_INFO "md: Skipping autodetection of RAID arrays. (raid=noautodetect)\n");
+		printk(KERN_INFO "md: Skipping autodetection of RAID arrays. (raid=autodetect will force)\n");
 	else
 		autodetect_raid();
 	md_setup_drive();