// Allocate a block if needed, otherwise figure
// out what the next block will be
if(thisBlock == POIFSConstants.END_OF_CHAIN) {
thisBlock = blockStore.getFreeBlock();
loopDetector.claim(thisBlock);
// We're on the end of the chain
nextBlock = POIFSConstants.END_OF_CHAIN;
// Mark the previous block as carrying on to us if needed