/* argument() function for device driver

SYNOPSIS

     #include "dd.h"

     s = argument(n);

     int n;             number of argument desired
     char *s;           n-th argument

DESCRIPTION

This function, when called from the init() function, returns the text of the
n-th argument in the line in the CONFIG.SYS file used to install the driver.
The 0-th argument is the file specification for the driver.  If there is no
n-th argument, the function returns NULL.  If the argument is more than 64
characters long, it is truncated to that length.  For example, if the driver
is installed by the following line

     DEVICE=RAMDISK.SYS 200 64

then

     argument(0)  is  "RAMDISK.SYS"
     argument(1)  is  "200"
     argument(2)  is  "64"
     argument(3)  is  NULL

CAUTION

The function uses a single internal buffer, so the returned string is
destroyed by the next call.  If it is called from outside the init()
function, it will return nonsense.  It uses the pointer 

     request_header->x.init.pointer.command_line

which overlays the pointer

     request_header->x.init.pointer.bpb_table

Therefore, it cannot be successfully called after the latter pointer has been
initialized by a block device driver.

*/

#include "dd.h"

#define MAXIMUM_ARGUMENT_LENGTH 64

char *argument(n) int n; {
static char buffer[MAXIMUM_ARGUMENT_LENGTH+1];
char *p;
int c;
p = request_header->x.init.pointer.command_line;
c = *p++;
while (n>=0) {
  int i;
  while (c==' ' || c=='\t' || c==0) c = *p++;
  if (c=='\r' || c=='\n') return NULL;
  i = 0;
  while (c!=' ' && c!='\t' && c!=0 && c!='\r' && c!='\n') {
    if (i<MAXIMUM_ARGUMENT_LENGTH) buffer[i++] = c;
    c = *p++;
    }
  buffer[i] = 0;
  n--;
  }
return buffer;
}