Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Path: utzoo!linus!decvax!ittvax!sii!mem
From: mem@sii.UUCP (Mark Mallett)
Newsgroups: net.micro.cpm
Subject: Re: Determining free disk space
Message-ID: <358@sii.UUCP>
Date: Thu, 22-Dec-83 01:19:12 EST
Article-I.D.: sii.358
Posted: Thu Dec 22 01:19:12 1983
Date-Received: Fri, 23-Dec-83 01:18:19 EST
Lines: 188

b
In response to the question of how to determine free space under
CP/M: CP/M keeps in memory an allocation bitmap for all LOGGED IN
drives.  The easiest way to determine freespace on a disc is to
make sure the drive is logged in, and then to look at the allocation
bitmap.  This is possible under CP/M 2.2 as you can find out where
this bitmap is kept.

What follows is an Aztec C routine `frespc' which determines the
free space on a given drive (assumed to be logged in).  This routine
is extracted from my program VDIR (a `dired'-like program for CP/M).
Preceding the routine is some definitions from VDIR.H which apply
to the routine.  I hope that this is useful. -mm

----------------------------------------------------------------------
typedef	char		BYTE;
typedef	int		BOOL;
typedef	int		WORD;
typedef	long		LONG;

#define	IND	static		/* For variables with no allocation
				    dependancies (don't have to be
				    on the stack) */


/* CP/M call codes */

#define	_MRICC	1		/* Input console character */
#define	_MROCC	2		/* Output console character */
#define	_MRPTR	3		/* Read paper tape */
#define	_MRPTP	4		/* Write paper tape */
#define	_MRLPT	5		/* Write LPT */
#define	_MRDCIO	6		/* Direct console I/O */
#define	_MRRIO	7		/* Read IO status */
#define	_MRSIO	8		/* Write IO status */
#define	_MRWCS	9		/* Write string to console */
#define	_MRRBC	10		/* Read buffer from console */
#define	_MRRCS	11		/* Read console status */
#define	_MRLFH	12		/* Lift head */
#define	_MRINI	13		/* Init BDOS */
#define	_MRSEL	14		/* Select and login a disk */
#define	_MROPN	15		/* Open a file */
#define	_MRCLS	16		/* Close a file */
#define	_MRSFL	17		/* Search for file */
#define	_MRSNF	18		/* Search for next file */
#define	_MRDEL	19		/* Delete a file */
#define	_MRREA	20		/* Read next record */
#define	_MRWRT	21		/* Write next record */
#define	_MRCRF	22		/* Create file */
#define	_MRREN	23		/* Rename file */
#define	_MRILV	24		/* Interrogate login vector */
#define	_MRIDN	25		/* Get drive number */
#define	_MRDMA	26		/* Set DMA address */
#define	_MRIAL	27		/* Get allocation vector */
#define	_MRWPD	28		/* Write-protect disc */
#define	_MRROV	29		/* Get R/O vector */
#define	_MRSFA	30		/* Set file attributes */
#define	_MRGDP	31		/* Get disc parms */
#define	_MRGUC	32		/* Get/set user code */
#define	_MRRRR	33		/* Read random record */
#define	_MRWRR	34		/* Write random record */
#define	_MRCFS	35		/* Compute file size */
#define	_MRSRR	36		/* Set random record */
#define	_MRWRZ	37		/* Write random record with zero fill */


/* Bios calls */

#define	_CBBOOT	0		/* Cold boot */
#define	_CBWBOOT 1		/* Warm boot */
#define	_CBCNST	2		/* Console status */
#define	_CBCNIN	3		/* Console input */
#define	_CBCNOUT 4		/* Console out */
#define	_CBLIST	5		/* Write to listing */
#define	_CBPUN	6		/* Write to punch */
#define	_CBRDR	7		/* Read from reader */
#define	_CBHOME	8		/* Home the disk */
#define	_CBSEL	9		/* Select disc */
#define	_CBSTRK	10		/* Set track */
#define	_CBSSEC	11		/* Set sector */
#define	_CBSDMA	12		/* Set DMA */
#define	_CBREAD	13		/* Read sector */
#define	_CBWRT	14		/* Write sector */
#define	_CBLSST	15		/* List status */
#define	_CBSTRN	16		/* Sector translate */


/* Structures used */




/* Disk parameter block */

typedef
  struct DPBs
    {
    WORD		DPB_SPT;		/* Sectors per track */
    BYTE		DPB_BSH;		/* Allocation shift factor */
    BYTE		DPB_BLM;		/* Allocation mask */
    BYTE		DPB_EXM;		/* Extent mask */
    WORD		DPB_DSM;		/* Storage mask */
    WORD		DPB_DRM;		/* Directory sizer */
    BYTE		DPB_AL0;
    BYTE		DPB_AL1;
    WORD		DPB_CKS;		/* Directory check vector */
    WORD		DPB_OFF;		/* Number of reserved tracks */
    }
  DPB;


/* Disc parameter header */

typedef
  struct DPHs
    {
    BYTE		*DPH_XLT;		/* Translate table */
    WORD		DPH_SCR[3];		/* Scratch */
    BYTE		*DPH_DIR;		/* Directory scratch */
    DPB			*DPH_DPB;		/* Pointer to DPB */
    BYTE		*DPH_CSV;		/* Checkpoint area */
    BYTE		*DPH_ALV;		/* Allocation area */
    }
  DPH;



/* frespc (drvnum)

	Find free space on drive drvnum

Accepts :

	drvnum		Drive number


Returns

	<value>		Number of K free on the drive.

*/

int frespc (drvnum)

int		drvnum;			/* Drive number */

{
IND	BYTE		*Bptr;		/* Allocation pointer */
IND	DPB		*DPBptr;
IND	DPH		*DPHptr;
IND	int		btotl;		/* Total blocks */
IND	int		blib;		/* Bits left-in-byte */
IND	int		i;		/* Scratch */
IND	WORD		albyte;		/* Allocation byte */

DPHptr = bioshl (_CBSEL, drvnum, 0);
DPBptr = bdoshl (_MRGDP, drvnum);

i = DPBptr -> DPB_DSM+1;		/* Number of blocks */
btotl = 0;				/* Total blocks */
blib = 0;				/* Bits-left-in-byte */
Bptr = DPHptr -> DPH_ALV;		/* Pointer to allocation byte */

while (i--)				/* DO all of them */
    {
    if (blib == 0)
	{
	albyte = *Bptr++;
	blib = 8;
	}

    if ((albyte & 0x80))
	btotl++;
    albyte = albyte << 1;
    blib--;
    }

btotl = DPBptr -> DPB_DSM + 1 - btotl;	/* Blocks left */
btotl = btotl * ((DPBptr -> DPB_BLM +1)/8);

return (btotl);

}

----------------------------------------------------------------------

Mark E. Mallett
decvax!sii!mem