/* * Get or Set or 'Get and Set' the cluster'th entry in the FAT. * * function - whether to get or set a fat entry * pmp - address of the msdosfsmount structure for the filesystem * whose FAT is to be manipulated. * cn - which cluster is of interest * oldcontents - address of a word that is to receive the contents of the * cluster'th entry if this is a get function * newcontents - the new value to be written into the cluster'th element of * the FAT if this is a set function. * * This function can also be used to free a cluster by setting the FAT entry * for a cluster to 0. * * All copies of the FAT are updated if this is a set function. NOTE: If * fatentry() marks a cluster as free it does not update the inusemap in * the msdosfsmount structure. This is left to the caller. */