STRIPE_EXPAND_READY
if (test_bit(STRIPE_EXPAND_READY, &sh->state))
set_bit(STRIPE_EXPAND_READY, &sh2->state);
s->expanded = test_bit(STRIPE_EXPAND_READY, &sh->state) && !sh->batch_head;
clear_bit(STRIPE_EXPAND_READY, &sh->state);
set_bit(STRIPE_EXPAND_READY, &sh->state);
(1 << STRIPE_EXPAND_READY) |\