filesys.c -- file system support functions
Version 11 -- 1987-06-03 -- D.N. Lynx Crowe

These functions support a {MS,GEM}DOS-like file system.
Subdirectories are not supported in this version.

Variables:
----------

	struct	bpb	*_thebpb;
	struct	dirent	_thedir[MAXDIRNT];
	struct	dirent	*_dptr;

	short	_thefat[MAXFAT * WDPSEC];

	int	_fatin, _dirin, _bpbin;
	long	_berrno;

Functions:
----------

	ClusMap(fcp)
	SnapFCB(fcp)

	_cl2lsn(bpp, clnum)
	_deadio(fcp)
	_dsrch(de)
	_fmake(fcp)
	_fsize(fcp)
	_ftrnc(dp)
	_getfat(bufad, bpp, nfat)
	_gtcl12(fat, cl)
	_inifcb(fcp, name,ext, mode)
	_nsic(fcp, bpp, fp)
	_opfcb(fcp)
	_ptcl12(fat, cl, val)
	_rdfat(bufad, bpp)
	_rdroot(buf, bpp)
	_rdsec(fcp, buf, ns)
	_seek(fcp)
	_sksec(fcp, sec)

_cl2lsn(bpp, clnum)

	Returns the logical sector number for cluster 'clnum' using the BPB
	pointed to by 'bpp'.

	int
	_cl2lsn(bpp, clnum)
	struct bpb *bpp;
	int clnum;


_ptcl12(fat, cl, val)

	Puts 'val' into cluster 'cl' in the FAT at 'fat'.

	putlc12(fat, cl, val)
	register char *fat;
	int cl, val;

_gtcl12(fat, cl)

	Returns the 12 bit cluster entry 'cl' from the FAT pointed to by 'fat'.

	int
	_gtcl12(fat, cl)
	register char *fat;
	int cl;

_getfat(bufad, bpp, nfat)

	Gets the FAT 'nfat' into the buffer pointed to by 'bufad' using
	the BPB pointed to by 'bpp'.

	int
	_getfat(bufad, bpp, nfat)
	int *bufad, nfat;
	register struct bpb *bpp;

_rdfat(bufad, bpp)

	Reads the FAT into the buffer pointed to by 'bufad'using the BPB
	pointed to by 'bpp'.

	int
	_rdfat(bufad, bpp)
	int *bufad;
	struct bpb *bpp;

_rdroot(buf, bpp)

	Reads the root directory into the buffer pointed to by 'buf'
	using the BPB pointed to by 'bpp'.

	int
	_rdroot(buf, bpp)
	int *buf;
	register struct bpb *bpp;

_nsic(fcp, bpp, fp)

	Gets the next sector in the file controlled by the FCB at 'fcp',
	using the BPB pointed to by 'bpp' and the FAT pointed to by 'fp'.
	Returns:  0 if successful, -1 on error, or 1 on EOF;

	int
	_nsic(fcp, bpp, fp)
	register struct fcb *fcp;
	struct bpb *bpp;
	char *fp;

_dsrch(de)

	Searches for the directory entry pointed to by 'de' in
	the current directory.

	struct dirent *
	_dsrch(de)
	register struct dirent *de;

_deadio(fcp)

	Marks the FCB pointed to by 'fcp' as 'in error'.

	_deadio(fcp)
	register struct fcb *fcp;

_seek(fcp)

	Seeks to to logical sector number in FCB pointed to by 'fcp'
	Returns:  -1 = error, 0 = OK, 1 = EOF.

	int
	_seek(fcp)
	register struct fcb *fcp;

_ftrnc(dp)

	Truncates the file pointed to by directory entry 'dp'.

	int
	_ftrnc(dp)
	struct dirent *dp;

_fmake(fcp)

	Makes a new file from the FCB pointed to by 'fcp'.

	int
	_fmake(fcp)
	struct fcb *fcp;

_opfcb(fcp)

	Opens the FCB pointed to by 'fcp'.  Returns 0 if opened successfully,
	-1 if an error occurred, with the error code in errno.

	int
	_opfcb(fcp)
	register struct fcb *fcp;

_inifcb(fcp, name,ext, mode)

	Initializes the FCB pointed to by 'fcp' for the file named 'name'.'ext'
	in mode 'mode'.  Returns 0 if ok, -1 if not.

	int
	_inifcb(fcp, name, ext, mode)
	register struct fcb *fcp;
	char *name, *ext;
	int mode;

_sksec(fcp, sec)

	Seeks the FCB pointed to by 'fcp' to sector 'sec'.
	Returns: -1 = error, 0 = OK, 1 = EOF

	int
	_sksec(fcp, sec)
	struct fcb *fcp;
	long sec;

_fsize(fcp)

	Returns the size, in sectors, of the file associated with
	the FCB pointed to by 'fcp', or -1 if the FCB isn't open.

	int
	_fsize(fcp)
	struct fcb *fcp;

_rdsec(fcp, buf, ns)

	Reads 'ns' sectors into the buffer at 'buf' from the file associated
	with the FCB pointed to b 'fcp'.  Returns 0 if OK, -1 if not.

	int
	_rdsec(fcp, buf, ns)
	struct fcb *fcp;
	char *buf;
	long ns;

ClusMap(fcp)

	Prints a map of the clusters for the file associated with
	the FCB pointed to by 'fcp'.  Ignored if file isn't open.
	Returns 0 if map was printed, -1 otherwise.

	int
	ClusMap(fcp)
	struct fcb *fcp;

SnapFCB(fcp)

	Prints the contents of an FCB pointed to by 'fcp'.  Only included
	in test versions of 'filesys.c' where TESTER is defined non-zero.

	SnapFCB(fcp)
	struct fcb *fcp;