mblock_alloc
if (mblock_alloc(mc, U_ADD, nmblocks) < 0)
if (mblock_alloc(mc_new, U_DEL, nmblocks + 1) < 0)
static int mblock_alloc(mpo_config_t *, update_t, int nmblocks);
if (mblock_alloc(&new_config, U_ADD_ALL, n_mblocks) < 0) {