EdkCompatibilityPkg/Sample/Tools/Source/GenBootsector/GetDrvNumOffset.c

   1 #include "fat.h"
   2 #include <stdio.h>
   3
   4 INTN
   5 GetDrvNumOffset (
   6   IN VOID *BootSector
   7   )
   8 {
   9   FAT_BPB_STRUCT  *FatBpb;
  10   UINTN           RootDirSectors;
  11   UINTN           FATSz;
  12   UINTN           TotSec;
  13   UINTN           DataSec;
  14   UINTN           CountOfClusters;
  15
  16   FatBpb  = (FAT_BPB_STRUCT *) BootSector;
  17
  18   //
  19   // Check FAT type algorithm from FAT spec
  20   //
  21   RootDirSectors = ((FatBpb->Fat12_16.BPB_RootEntCnt * sizeof(FAT_DIRECTORY_ENTRY)) +
  22                     (FatBpb->Fat12_16.BPB_BytsPerSec - 1)) / FatBpb->Fat12_16.BPB_BytsPerSec;
  23
  24   if (FatBpb->Fat12_16.BPB_FATSz16 != 0) {
  25     FATSz = FatBpb->Fat12_16.BPB_FATSz16;
  26   } else {
  27     FATSz = FatBpb->Fat32.BPB_FATSz32;
  28   }
  29   if (FATSz == 0) {
  30     fprintf (stderr, "ERROR: FAT: BPB_FATSz16, BPB_FATSz32 - 0, expected - Non-Zero\n");
  31     return -1;
  32   }
  33
  34   if (FatBpb->Fat12_16.BPB_TotSec16 != 0) {
  35     TotSec = FatBpb->Fat12_16.BPB_TotSec16;
  36   } else {
  37     TotSec = FatBpb->Fat12_16.BPB_TotSec32;
  38   }
  39   if (TotSec == 0) {
  40     fprintf (stderr, "ERROR: FAT: BPB_TotSec16, BPB_TotSec32 - 0, expected - Non-Zero\n");
  41     return -1;
  42   }
  43
  44   DataSec = TotSec - (
  45                       FatBpb->Fat12_16.BPB_RsvdSecCnt +
  46                       FatBpb->Fat12_16.BPB_NumFATs * FATSz +
  47                       RootDirSectors
  48                      );
  49
  50   CountOfClusters = DataSec / FatBpb->Fat12_16.BPB_SecPerClus;
  51
  52   if (CountOfClusters < FAT_MAX_FAT16_CLUSTER) {
  53     return (INTN) ((UINTN) &FatBpb->Fat12_16.BS_DrvNum - (UINTN) FatBpb);
  54   } else {
  55     return (INTN) ((UINTN) &FatBpb->Fat32.BS_DrvNum - (UINTN) FatBpb);
  56   }
  57 }
  58