typedef struct Source Source;typedef struct VacFile VacFile;typedef struct VacDirSource VacDirSource;typedef struct MetaBlock MetaBlock;typedef struct Lump Lump;typedef struct Cache Cache;typedef struct Super Super; struct VacFS {	int ref;		/* need a read write lock? */ 	uchar score[VtScoreSize];	VacFile *root;		VtSession *z;	int readOnly;	int bsize;		/* maximum block size */	uvlong qid;		/* next qid */	Cache *cache;}; struct VacFile {	int ref;	VtLock *lk;	VacFS *fs;		/* immutable */ 	int	used;	int	removed; 	Source *source;	Source *msource;	/* meta source: only for directories */		VacDir dir;		/* meta data for this file */ 	VacFile *up;	/* parent file */	VacFile *down;	/* children */	VacFile *next;	/* sibling */}; struct Source {	VtLock *lk; 	Cache *cache;	/* immutable */	int readOnly;	/* immutable */	Lump *lump;	/* lump containing dir entry */	int entry;	/* which entry in the block: immutable */ 	/* unpacked VtDirEntry */	ulong gen;	/* generation: immutable */	int dir;	/* dir flags: immutable */	int depth;	/* number of levels of pointer blocks */	int psize;	/* pointer block size: immutable */	int dsize;	/* data block size: immutable */	uvlong size2;	/* size in bytes of file */ 	int epb;	/* dir entries per block = dize/VtDirEntrySize: immutable */}; struct MetaBlock {	int size;	int free;	int maxindex;	int nindex;	uchar *buf;}; /* * contains a one block buffer * to avoid problems of the block changing underfoot * and to enable an interface that supports unget. */struct VacDirEnum {	VacFile *file;		ulong block;	/* current block */	MetaBlock mb;	/* parsed version of block */	int index;	/* index in block */	uchar *buf;	/* raw data of block */}; /* Lump states */enum {	LumpFree,	LumpVenti,	/* on venti server: score > 2^32: just a cached copy */	LumpActive,	/* active */	LumpActiveRO,	/* active: read only block */	LumpActiveA,	/* active: achrived */	LumpSnap,	/* snapshot: */	LumpSnapRO,	/* snapshot: read only */	LumpSnapA,	/* snapshot: achived */	LumpZombie,	/* block with no pointer to it: waiting to be freed */		LumpMax}; /* * Each lump has a state and generation * The following invariants are maintained * 	Each lump has no more than than one parent per generation * 	For Active*, no child has a parent of a greater generation *	For Snap*, there is a parent of given generation and there are *		no parents of greater gen - implies no children of a less gen *	For *RO, the lump is fixed - no change ca be made - all pointers *		are valid venti addresses *	For *A, the lump is on the venti server *	There are no pointers to Zombie lumps * * Transitions *	Archiver at generation g *	Mutator at generation h *	 *	Want to modify a lump *		Venti: create new Active(h) *		Active(x): x == h: do nothing *		Acitve(x): x < h: change to Snap(h) + add Active(h) *		ActiveRO(x): change to SnapRO(h) + add Active(h) *		ActiveA(x): add Active(h) *		Snap*(x): should not occur *		Zombie(x): should not occur *	Want to archive *		Active(x): x != g: should never happen *		Active(x): x == g fix children and free them: move to ActoveRO(g); *		ActiveRO(x): x != g: should never happen *		ActiveRO(x): x == g: wait until it hits ActiveA or SnapA *		ActiveA(x): done *		Active(x): x < g: should never happen *		Snap(x): x >= g: fix children, freeing all SnapA(y) x == y; *		SnapRO(x): wait until it hits SnapA * */  struct Lump {	int ref; 	Cache *c; 	VtLock *lk;		int state;	ulong gen; 	uchar 	*data;	uchar	score[VtScoreSize];	/* score of packet */	uchar	vscore[VtScoreSize];	/* venti score - when archived */	u8int	type;			/* type of packet */	int	dir;			/* part of a directory - extension of type */	u16int	size;			/* amount of data allocated */	Lump	*next;			/* doubly linked hash chains */	Lump	*prev;	u32int	heap;			/* index in heap table */	u32int	used;			/* last reference times */	u32int	used2; 	u32int	addr;			/* mutable block address */};