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                   Finding SSWAPed drives in C

If Stacker is installed, using the ST_PTR generated by the call to the detect_stacker() function as shown in Appendix B of the Stacker version 2 manual, it is possible to determine what drives have been swapped using SSWAP. At offset 0x52 from ST_PTR is a signature, which consists of the four characters 'SWAP'. Following this four byte signature is a 26 byte array, which contains the original drive numbers (0=A, 1=B, etc) for all drives. Each time SSWAP performs a swap of two drives, it interchanges the corresponding entries in this array.

Using C notation, the structure is defined as follows:

ST_PTR + 52H –> struct swapmap

                  {
                  char swapSignature[4];    /*  'SWAP' */
                  char swapmap[26];
                  }

Note that swapmap[i] (where i=0 means A:, i=1 means B:, etc) contains the "original" drive number for drive i. That is, drive i was drive swapmap[i] at boot time. To find the inverse function (namely, what is the current drive number of the drive that was drive j at boot time?), you need to search the swapmap array to find j. In other words, if swapmap[k]==j, then drive k was drive j at boot time.