[PATCH] md: expose device slot information via sysfs

	providing an ongoing count for arrays with metadata managed by

	userspace.

      slot

        This gives the role that the device has in the array.  It will

	either be 'none' if the device is not active in the array

        (i.e. is a spare or has failed) or an integer less than the

	'raid_disks' number for the array indicating which possition

	it currently fills.  This can only be set while assembling an

	array.  A device for which this is set is assumed to be working.

An active md device will also contain and entry for each active device

in the array.  These are named

static struct rdev_sysfs_entry rdev_errors =

__ATTR(errors, 0644, errors_show, errors_store);

static ssize_t

slot_show(mdk_rdev_t *rdev, char *page)

{

	if (rdev->raid_disk < 0)

		return sprintf(page, "none\n");

	else

		return sprintf(page, "%d\n", rdev->raid_disk);

}

static ssize_t

slot_store(mdk_rdev_t *rdev, const char *buf, size_t len)

{

	char *e;

	int slot = simple_strtoul(buf, &e, 10);

	if (strncmp(buf, "none", 4)==0)

		slot = -1;

	else if (e==buf || (*e && *e!= '\n'))

		return -EINVAL;

	if (rdev->mddev->pers)

		/* Cannot set slot in active array (yet) */

		return -EBUSY;

	if (slot >= rdev->mddev->raid_disks)

		return -ENOSPC;

	rdev->raid_disk = slot;

	/* assume it is working */

	rdev->flags = 0;

	set_bit(In_sync, &rdev->flags);

	return len;

}

static struct rdev_sysfs_entry rdev_slot =

__ATTR(slot, 0644, slot_show, slot_store);

static struct attribute *rdev_default_attrs[] = {

	&rdev_state.attr,

	&rdev_super.attr,

	&rdev_errors.attr,

	&rdev_slot.attr,

	NULL,

};

static ssize_t