[PATCH] md: factor out MD superblock handling code

Define an interface for interpreting and updating superblocks
so we can more easily define new formats.

With this patch, (almost) all superblock layout information is
locating in a small set of routines dedicated to superblock
handling.  This will allow us to provide a similar set for
a different format.

The two exceptions are:
 1/ autostart_array where the devices listed in the superblock
    are searched for.
 2/ raid5 'knows' the maximum number of devices for
     compute_parity.

These will be addressed in a later patch.

drivers/md/multipath.c

@@ -59,7 +59,7 @@ static void mp_pool_free(void *mpb, void *data)
 static int multipath_map (mddev_t *mddev, mdk_rdev_t **rdevp)
 {
 	multipath_conf_t *conf = mddev_to_conf(mddev);
-	int i, disks = MD_SB_DISKS;
+	int i, disks = mddev->max_disks;
 
 	/*
 	 * Later we do read balancing on the read side 
@@ -147,7 +147,7 @@ static int multipath_read_balance (multipath_conf_t *conf)
 {
 	int disk;
 
-	for (disk = 0; disk < MD_SB_DISKS; disk++) {
+	for (disk = 0; disk < conf->mddev->max_disks; disk++) {
 		mdk_rdev_t *rdev = conf->multipaths[disk].rdev;
 		if (rdev && rdev->in_sync)
 			return disk;
@@ -259,7 +259,7 @@ static void print_multipath_conf (multipath_conf_t *conf)
 	printk(" --- wd:%d rd:%d\n", conf->working_disks,
 			 conf->raid_disks);
 
-	for (i = 0; i < MD_SB_DISKS; i++) {
+	for (i = 0; i < conf->mddev->max_disks; i++) {
 		tmp = conf->multipaths + i;
 		if (tmp->rdev)
 			printk(" disk%d, o:%d, dev:%s\n",

include/linux/raid/md_k.h

@@ -151,8 +151,9 @@ struct mdk_rdev_s
 	struct block_device *bdev;	/* block device handle */
 
 	struct page	*sb_page;
-	mdp_super_t	*sb;
+	int		sb_loaded;
 	sector_t	sb_offset;
+	int		preferred_minor;	/* autorun support */
 
 	/* A device can be in one of three states based on two flags:
 	 * Not working:   faulty==1 in_sync==0
@@ -196,6 +197,7 @@ struct mddev_s
 	time_t				ctime, utime;
 	int				level, layout;
 	int				raid_disks;
+	int				max_disks;
 	unsigned long			state;
 	sector_t			size; /* used size of component devices */
 	__u64				events;