[PATCH] md: export rdev->data_offset via sysfs

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

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

      offset

        This gives the location in the device (in sectors from the

        start) where data from the array will be stored.  Any part of

        the device before this offset us not touched, unless it is

        used for storing metadata (Formats 1.1 and 1.2).

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_slot =

__ATTR(slot, 0644, slot_show, slot_store);

static ssize_t

offset_show(mdk_rdev_t *rdev, char *page)

{

	return sprintf(page, "%llu\n", rdev->data_offset);

}

static ssize_t

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

{

	char *e;

	unsigned long long offset = simple_strtoull(buf, &e, 10);

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

		return -EINVAL;

	if (rdev->mddev->pers)

		return -EBUSY;

	rdev->data_offset = offset;

	return len;

}

static struct rdev_sysfs_entry rdev_offset =

__ATTR(offset, 0644, offset_show, offset_store);

static struct attribute *rdev_default_attrs[] = {

	&rdev_state.attr,

	&rdev_super.attr,

	&rdev_errors.attr,

	&rdev_slot.attr,

	&rdev_offset.attr,

	NULL,

};

static ssize_t