81 lines
2.4 KiB
C
81 lines
2.4 KiB
C
/*
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* fat.c
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*
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* Created on: Aug 31, 2011
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* Author: Tiberiu
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*/
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#include <fileio.h>
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#include <debugio.h>
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#include "fat.h"
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// Buffer should contain boot sector
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uint32 FatDetect (void* buffer)
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{
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FatBootSector* boot = (FatBootSector*)buffer;
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uint32 correct_features = 0;
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uint32 total_features = 0;
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// Try the asm 'jmp' instruction
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if ((boot->bpb.AsmJmp[0] == 0x6B || boot->bpb.AsmJmp[0]==0xEB) && boot->bpb.AsmJmp[2] == 0x90)
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correct_features++;
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total_features ++;
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// Try the OemId. First char is often 'm' or 'M' (mkdosfs or MSDOS??/MSWIN??)
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if (boot->bpb.OemId[0] == 'm' || boot->bpb.OemId[0] == 'M') correct_features++;
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total_features ++;
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// Try the bytes per sector. Most often, it is 512.
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if (boot->bpb.BytesPerSector == 512) correct_features++;
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total_features ++;
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// Try the sectors per cluster. This is always a power of 2.
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uint8 sectclust = boot->bpb.SectorsPerCluster;
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uint8 count = 0;
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while (sectclust) { count += sectclust&1; sectclust>>=1; }
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if (count != 1) return 0;
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// Number of fats, can be 2 or (rarely) 1. Important feature.
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if (boot->bpb.FatsCount == 1 || boot->bpb.FatsCount == 2) correct_features+=2;
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total_features+=2;
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// This tells us what type of disk this is. Usually values are above 0xf0.
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if (boot->bpb.MediaDescriptorType >= 0xF0) correct_features++;
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total_features++;
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// Calculate number of clusters
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uint32 clusters = (boot->bpb.TotalSectors * boot->bpb.SectorsPerCluster);
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if (clusters == 0) clusters = (boot->bpb.TotalSectorsLarge * boot->bpb.SectorsPerCluster);
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// Calculate fat type
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uint32 fat = (clusters < 4085) ? 12 : 16 ;
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if (clusters > 65524) fat = 32;
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// Try the extended info
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if (fat == 32) {
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if (boot->ext.fat32.Signature == 0x28 || boot->ext.fat32.Signature == 0x29) correct_features++;
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total_features++;
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}
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else {
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if (boot->ext.fat16.Signature == 0x28 || boot->ext.fat16.Signature == 0x29) correct_features++;
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total_features++;
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}
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Log("Fat", "Correct features: %u out of %u. Type should be fat%u.\n", correct_features, total_features, fat);
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// See what we have.
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if (correct_features > (total_features/2)) return 0; // insuficcient correct features?
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return fat; // return FAT type
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}
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void FatInstall()
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{
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FileSystem fat12 = {0, "fat12", Fat12Detect, 0,0,0,0,0,0,0,0};
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FileSystem fat16 = {0, "fat16", Fat16Detect, 0,0,0,0,0,0,0,0};
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FileSystem fat32 = {0, "fat32", Fat32Detect, 0,0,0,0,0,0,0,0};
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VfsInstallFs(&fat12); VfsInstallFs(&fat16); VfsInstallFs(&fat32);
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}
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