calc_mirror_idx_from_commit
u32 idx = calc_mirror_idx_from_commit(data->lseg, data->ds_commit_index);
idx = calc_mirror_idx_from_commit(cdata->lseg, cdata->ds_commit_index);
idx = calc_mirror_idx_from_commit(cdata->lseg, cdata->ds_commit_index);
idx = calc_mirror_idx_from_commit(lseg, data->ds_commit_index);