mirror of https://github.com/acidanthera/audk.git
59 lines
1.6 KiB
C
59 lines
1.6 KiB
C
#include "fat.h"
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#include <stdio.h>
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INTN
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GetDrvNumOffset (
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IN VOID *BootSector
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)
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{
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FAT_BPB_STRUCT *FatBpb;
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UINTN RootDirSectors;
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UINTN FATSz;
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UINTN TotSec;
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UINTN DataSec;
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UINTN CountOfClusters;
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FatBpb = (FAT_BPB_STRUCT *) BootSector;
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//
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// Check FAT type algorithm from FAT spec
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//
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RootDirSectors = ((FatBpb->Fat12_16.BPB_RootEntCnt * sizeof(FAT_DIRECTORY_ENTRY)) +
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(FatBpb->Fat12_16.BPB_BytsPerSec - 1)) / FatBpb->Fat12_16.BPB_BytsPerSec;
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if (FatBpb->Fat12_16.BPB_FATSz16 != 0) {
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FATSz = FatBpb->Fat12_16.BPB_FATSz16;
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} else {
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FATSz = FatBpb->Fat32.BPB_FATSz32;
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}
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if (FATSz == 0) {
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fprintf (stderr, "ERROR: FAT: BPB_FATSz16, BPB_FATSz32 - 0, expected - Non-Zero\n");
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return -1;
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}
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if (FatBpb->Fat12_16.BPB_TotSec16 != 0) {
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TotSec = FatBpb->Fat12_16.BPB_TotSec16;
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} else {
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TotSec = FatBpb->Fat12_16.BPB_TotSec32;
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}
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if (TotSec == 0) {
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fprintf (stderr, "ERROR: FAT: BPB_TotSec16, BPB_TotSec32 - 0, expected - Non-Zero\n");
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return -1;
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}
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DataSec = TotSec - (
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FatBpb->Fat12_16.BPB_RsvdSecCnt +
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FatBpb->Fat12_16.BPB_NumFATs * FATSz +
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RootDirSectors
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);
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CountOfClusters = DataSec / FatBpb->Fat12_16.BPB_SecPerClus;
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if (CountOfClusters < FAT_MAX_FAT16_CLUSTER) {
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return (INTN) ((UINTN) &FatBpb->Fat12_16.BS_DrvNum - (UINTN) FatBpb);
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} else {
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return (INTN) ((UINTN) &FatBpb->Fat32.BS_DrvNum - (UINTN) FatBpb);
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}
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}
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