dm_rh_get_state
int state = dm_rh_get_state(ms->rh, region, may_block);
state = dm_rh_get_state(ms->rh, region, 1);
EXPORT_SYMBOL_GPL(dm_rh_get_state);
int dm_rh_get_state(struct dm_region_hash *rh, region_t region, int may_block);