typedef struct Disk	Disk; /* *  Reference to the disk */struct Disk{	Bcache;	ulong	nb;	/* number of blocks */	ulong	nab;	/* number of allocation blocks */	int	b2b;	/* allocation bits to a block */	int	p2b;	/* Dptr's per page */	char	name[CACHENAMELEN];}; int	dinit(Disk*, int, int, char*);int	dformat(Disk*, int, char*, ulong, ulong);ulong	dalloc(Disk*, Dptr*);ulong	dpalloc(Disk*, Dptr*);int	dfree(Disk*, Dptr*); extern int debug; #define DPRINT if(debug)fprint