BaseTools/Source/C/GenBootSector/GetDrvNumOffset.c

   1 /** @file
   2
   3   Get Drv Num offset from Fat file system.
   4
   5 Copyright (c) 2006 - 2018, Intel Corporation. All rights reserved.<BR>
   6 This program and the accompanying materials
   7 are licensed and made available under the terms and conditions of the BSD License
   8 which accompanies this distribution.  The full text of the license may be found at
   9 http://opensource.org/licenses/bsd-license.php
  10
  11 THE PROGRAM IS DISTRIBUTED UNDER THE BSD LICENSE ON AN "AS IS" BASIS,
  12 WITHOUT WARRANTIES OR REPRESENTATIONS OF ANY KIND, EITHER EXPRESS OR IMPLIED.
  13
  14 **/
  15
  16 #include <stdio.h>
  17 #include "FatFormat.h"
  18
  19 INTN
  20 GetDrvNumOffset (
  21   IN VOID *BootSector
  22   )
  23 {
  24   FAT_BPB_STRUCT  *FatBpb;
  25   UINTN           RootDirSectors;
  26   UINTN           FATSz;
  27   UINTN           TotSec;
  28   UINTN           DataSec;
  29   UINTN           CountOfClusters;
  30
  31   FatBpb  = (FAT_BPB_STRUCT *) BootSector;
  32
  33   //
  34   // Check FAT type algorithm from FAT spec
  35   //
  36   RootDirSectors = ((FatBpb->Fat12_16.BPB_RootEntCnt * sizeof(FAT_DIRECTORY_ENTRY)) +
  37                     (FatBpb->Fat12_16.BPB_BytsPerSec - 1)) / FatBpb->Fat12_16.BPB_BytsPerSec;
  38
  39   if (FatBpb->Fat12_16.BPB_FATSz16 != 0) {
  40     FATSz = FatBpb->Fat12_16.BPB_FATSz16;
  41   } else {
  42     FATSz = FatBpb->Fat32.BPB_FATSz32;
  43   }
  44   if (FATSz == 0) {
  45     fprintf (stderr, "error E3003: FAT - BPB_FATSz16, BPB_FATSz32 - 0, expected: Non-Zero number\n");
  46     return -1;
  47   }
  48
  49   if (FatBpb->Fat12_16.BPB_TotSec16 != 0) {
  50     TotSec = FatBpb->Fat12_16.BPB_TotSec16;
  51   } else {
  52     TotSec = FatBpb->Fat12_16.BPB_TotSec32;
  53   }
  54   if (TotSec == 0) {
  55     fprintf (stderr, "error E3003: FAT - BPB_TotSec16, BPB_TotSec32 - 0, expected: Non-Zero number\n");
  56     return -1;
  57   }
  58
  59   DataSec = TotSec - (
  60                       FatBpb->Fat12_16.BPB_RsvdSecCnt +
  61                       FatBpb->Fat12_16.BPB_NumFATs * FATSz +
  62                       RootDirSectors
  63                      );
  64
  65   CountOfClusters = DataSec / FatBpb->Fat12_16.BPB_SecPerClus;
  66
  67   if (CountOfClusters < FAT_MAX_FAT16_CLUSTER) {
  68     return (INTN) ((UINTN) &FatBpb->Fat12_16.BS_DrvNum - (UINTN) FatBpb);
  69   } else {
  70     return (INTN) ((UINTN) &FatBpb->Fat32.BS_DrvNum - (UINTN) FatBpb);
  71   }
  72 }
  73