Category : C Source Code
Archive : PDTAR.ZIP
Filename : DOSIO.C
Output of file : DOSIO.C contained in archive : PDTAR.ZIP
* Dos direct-disk I/O routines for PDTAR
* By E. Roskos 2/88
* For Minix-compatible multivolume tar implementation under DOS
*
* These routines are based on my Minix "build" I/O code, although
* changed a lot...
*/
#ifdef MSDOS
#include
#include
#include
extern int physdrv;
extern int devsize;
extern int ftty;
static long curblk = 0;
static int inited = 0;
/*
* Local I/O buffers. We do the actual disk I/O to one of these two.
* The reason is that we select which one we'll use, and set iobuf to
* point to it, in order to get a block of memory that doesn't cross
* a 64K boundary -- because the DMA controller can't do I/O across
* a 64K boundary.
*/
static char buf1[512], buf2[512];
static char *iobuf;
/*
* DMAoverrun checks whether buff1 crosses a 64K boundary.
*/
static int
DMAoverrun(buff1)
char *buff1;
{
int i;
i = (int)buff1;
return(i > i + 512);
}
/*
* absio does absolute disk I/O, using the ROM BIOS
* It performs BIOS operation "fn", on "drive", specifying
* block number "blocknr" and buffer "buff" (which must
* be in the single (small-model) data segment).
* Note that the block numbering scheme corresponds to the
* Minix, PC/IX, and DOS 2.x block numbering, not the DOS
* 3.x block numbering.
*/
static int
absio(fn, drive, blocknr, buff)
int fn;
int drive;
long blocknr;
char *buff;
{
union REGS iregs;
union REGS oregs;
int track;
iregs.h.ah = fn;
iregs.h.dl = drive;
track = blocknr / 9;
iregs.h.dh = track & 1;
iregs.h.ch = track >> 1;
iregs.h.cl = (blocknr % 9) + 1;
iregs.h.al = 1;
iregs.x.bx = (int)buff;
int86(0x13, &iregs, &oregs);
if (oregs.x.cflag)
{
#ifdef DEBUGIO
fprintf(stderr, "absio: error %sing drv %c block %d address %x: bios code %x\n",
fn==2? "read" : "writ", 'A'+drive, blocknr, buff, oregs.h.ah&0xff);
#endif /* DEBUGIO */
return(oregs.h.ah&0xff);
}
else
{
return(0);
}
}
/*
* initdiskio initializes the floppy disk subsystem and selects
* a local buffer for us to use, if this is the first time it is
* called. Otherwise, it does nothing.
*/
static void
initdskio()
{
if (!inited)
{
absio(0, 0, 0, 0);
if (DMAoverrun(buf1))
iobuf = buf2;
else
iobuf = buf1;
inited++;
}
}
/*
* absread performs an absolute disk read of "drive"'s block
* "blocknr", reading into the buffer at "buff".
*/
static int
absread(drive, blocknr, buff)
int drive;
long blocknr;
char *buff;
{
int err;
initdskio();
err = absio(2, drive, blocknr, iobuf);
if (!err)
memcpy(buff, iobuf, 512);
return(err);
}
/*
* abswrite performs an absolute disk write of "drive"'s block
* "blocknr", reading into the buffer at "buff".
*/
static int
abswrite(drive, blocknr, buff)
int drive;
long blocknr;
char *buff;
{
int err;
initdskio();
memcpy(iobuf, buff, 512);
return(absio(3, drive, blocknr, iobuf));
}
/*
* physrw reads or writes the data at "buf" for length "len", which
* must be a multiple of 512 bytes; it reads if fread is 1, or writes
* if fread is 0. The data is read/written on the next consecutive
* block of the floppy disk; if the end of the disk has been reached
* (as determined by the disk size block count in the global variable
* devsize) it asks the user to change disks before it performs the I/O,
* then performs the I/O to block 0 of the new disk.
*/
static int
physrw(buf, len, fread)
char *buf;
int len;
int fread;
{
int err;
int errct = 0;
int nbytes;
static void diskerr();
nbytes = len; /* save for return value */
/* be sure size of xfer is a multiple of DOS physical block size */
if (len & 0x1ff)
{
fprintf(stderr, "tar: fatal error: phys disk I/O must be ");
fprintf(stderr, "multiple of 512 bytes\n");
exit(1);
}
/* convert byte count to DOS block count */
len >>= 9;
/* now read or write a block at a time into the buffer */
while (len > 0)
{
/* check for time to change disks */
if (curblk >= devsize)
{
uprintf(ftty, "\ntar: Change disks and press [Enter]: ");
while (ugetc(ftty)!='\n') ;
curblk = 0;
}
/* read or write the next block */
if (fread)
err = absread(physdrv, curblk, buf);
else
err = abswrite(physdrv, curblk, buf);
/* check for an error */
if (err)
{
diskerr(fread? "reading" : "writing",
physdrv, curblk, err);
errct++;
}
/* increment block number & buf addr, decrement count */
curblk++;
buf += 512;
len--;
}
if (errct)
return(-1);
else
return(nbytes);
}
/*
* physwrite is the "write" version of physrw, and is what is called
* from outside this package. It writes the data at "buf" for
* length "len", which must be a multiple of 512 bytes, as described
* above under "physrw".
*/
int
physwrite(buf, len)
char *buf;
int len;
{
return(physrw(buf, len, 0));
}
/*
* see comments for physwrite
*/
int
physread(buf, len)
char *buf;
int len;
{
return(physrw(buf, len, 1));
}
/*
* This routine prints an error message for disk I/O: the operation
* ("reading", "writing") is in s, the drive number in "drive",
* the sector number in "sectnum", and the BIOS AH return code
* is in "err".
*/
static void
diskerr(s,drive,sectnum,err)
int sectnum, err,drive;
char *s;
{
extern char *derrtab[];
char *mp;
fprintf(stderr, "Error %s drive %c, sector: %d, code: %d = '",
s, drive+'A',sectnum, err);
switch (err)
{
case 0:
mp = "No error";
break;
case 1:
mp = "Bad command passed to BIOS";
break;
case 2:
mp = "Address mark not found";
break;
case 3:
mp = "Disk is write protected";
break;
case 4:
mp = "Sector not found";
break;
case 8:
mp = "DMA overrun";
break;
case 9:
mp = "DMA crosses 64K boundary (internal error)";
break;
case 0x10:
mp = "Bad CRC on disk read";
break;
case 0x20:
mp = "Disk controller has failed";
break;
case 0x40:
mp = "Seek failed";
break;
case 0x80:
mp = "No response from controller";
break;
default:
mp = "Unknown error";
break;
}
fprintf(stderr,"%s'\n", mp);
}
#endif /* MSDOS */
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