/** @file | |
Get Drv Num offset from Fat file system. | |
Copyright (c) 2006 - 2018, Intel Corporation. All rights reserved.<BR> | |
This program and the accompanying materials | |
are licensed and made available under the terms and conditions of the BSD License | |
which accompanies this distribution. The full text of the license may be found at | |
http://opensource.org/licenses/bsd-license.php | |
THE PROGRAM IS DISTRIBUTED UNDER THE BSD LICENSE ON AN "AS IS" BASIS, | |
WITHOUT WARRANTIES OR REPRESENTATIONS OF ANY KIND, EITHER EXPRESS OR IMPLIED. | |
**/ | |
#include <stdio.h> | |
#include "FatFormat.h" | |
INTN | |
GetDrvNumOffset ( | |
IN VOID *BootSector | |
) | |
{ | |
FAT_BPB_STRUCT *FatBpb; | |
UINTN RootDirSectors; | |
UINTN FATSz; | |
UINTN TotSec; | |
UINTN DataSec; | |
UINTN CountOfClusters; | |
FatBpb = (FAT_BPB_STRUCT *) BootSector; | |
// | |
// Check FAT type algorithm from FAT spec | |
// | |
RootDirSectors = ((FatBpb->Fat12_16.BPB_RootEntCnt * sizeof(FAT_DIRECTORY_ENTRY)) + | |
(FatBpb->Fat12_16.BPB_BytsPerSec - 1)) / FatBpb->Fat12_16.BPB_BytsPerSec; | |
if (FatBpb->Fat12_16.BPB_FATSz16 != 0) { | |
FATSz = FatBpb->Fat12_16.BPB_FATSz16; | |
} else { | |
FATSz = FatBpb->Fat32.BPB_FATSz32; | |
} | |
if (FATSz == 0) { | |
fprintf (stderr, "error E3003: FAT - BPB_FATSz16, BPB_FATSz32 - 0, expected: Non-Zero number\n"); | |
return -1; | |
} | |
if (FatBpb->Fat12_16.BPB_TotSec16 != 0) { | |
TotSec = FatBpb->Fat12_16.BPB_TotSec16; | |
} else { | |
TotSec = FatBpb->Fat12_16.BPB_TotSec32; | |
} | |
if (TotSec == 0) { | |
fprintf (stderr, "error E3003: FAT - BPB_TotSec16, BPB_TotSec32 - 0, expected: Non-Zero number\n"); | |
return -1; | |
} | |
DataSec = TotSec - ( | |
FatBpb->Fat12_16.BPB_RsvdSecCnt + | |
FatBpb->Fat12_16.BPB_NumFATs * FATSz + | |
RootDirSectors | |
); | |
CountOfClusters = DataSec / FatBpb->Fat12_16.BPB_SecPerClus; | |
if (CountOfClusters < FAT_MAX_FAT16_CLUSTER) { | |
return (INTN) ((UINTN) &FatBpb->Fat12_16.BS_DrvNum - (UINTN) FatBpb); | |
} else { | |
return (INTN) ((UINTN) &FatBpb->Fat32.BS_DrvNum - (UINTN) FatBpb); | |
} | |
} | |