cg_clustersfree_swap
freemapp = cg_clustersfree_swap(cgp, needswap);
setbit(cg_clustersfree_swap(&acg, 0), blkno);
setbit(cg_clustersfree_swap(&acg, 0), blkno);
u_char *mapp = cg_clustersfree_swap(&acg, 0);