GetBlockGroup
status_t status = fVolume->GetBlockGroup(blockGroup, &fGroupDescriptor);
status_t status = fVolume->GetBlockGroup(blockGroup, &group);
status_t status = fVolume->GetBlockGroup(blockGroup, &group);
status_t status = GetBlockGroup((id - 1) / fSuperBlock.InodesPerGroup(),
status_t GetBlockGroup(int32 index,