typedef struct Db	Db;typedef struct Dbent	Dbent;typedef struct Meta	Meta;  enum {	Uidlen	= 10,	Uidslen	= 2 * Uidlen,	Incr	= 16, }; enum {	// cmpfile and syncfile values	Eq = 0,	Metachg,	Datachg,};  struct Meta {	char*	uid;	char*	gid;	ulong	mode;	ulong	mtime;	vlong	length;	ulong	vers;	// of qid}; struct Dbent {	Avl	a;	Dbent*	next;		// to link while outside the avl	char*	fname;		// stored in disk	char*	hist;		// stored in disk	int	hlen;	int	visited;	int	pruned;	Meta;			// stored in disk}; struct Db {	Avltree*tree;	char	id;	char*	dir;	Dbent*	new;		// waiting for insert into tee.	ulong	mtime;		// for last scan	int	changed;}; Db*	newdb(char id);Db*	readdb(Biobufhdr* bp);void	writedb(Biobufhdr* bp, Db* db);void	insertdb(Db* db, Dbent* dp);Db*	readdbfile(char* file);void	writedbfile(char* file, Db* db);void	rename(char* to, char*frompath);