85 lines
2.0 KiB
C++
85 lines
2.0 KiB
C++
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#include "fat.hpp"
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#include <cstring>
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namespace helos {
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namespace filesystem {
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FAT::~FAT() {
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if (sector)
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delete[](char *) sector;
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if (bpb)
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delete bpb;
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// either ebr or ebr32
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if (ebr) {
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if (type == FAT32)
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delete ebr32;
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else
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delete ebr;
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}
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}
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Filesystem *FAT::AllocateBlock(BlockDevice *block, FAT::Config *config) {
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FAT *fat = new FAT;
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fat->sector = new char[512];
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// read the first sector
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uint64_t read = block->ReadBlock(0, fat->sector, 1);
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if (read == 0) {
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delete fat;
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return nullptr;
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}
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// allocate the BPB
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fat->bpb = new BIOSParamBlock;
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memcpy(fat->bpb, fat->sector, sizeof(BIOSParamBlock));
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fat->numSectors = ((fat->bpb->numSectors_short != 0) ? fat->bpb->numSectors_short : fat->bpb->numSectors_large);
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// tell the filesystem FAT type
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if (fat->bpb->numBytesPerSector == 0) { // exFAT
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fat->type = exFAT;
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delete fat;
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return nullptr; // TODO exFAT is not supported
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} else if (fat->bpb->numSectorsPerFAT_12_16 == 0) { // FAT32
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fat->type = FAT32;
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fat->ebr32 = new ExtBootRecord_32;
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memcpy(fat->ebr32, (char *)fat->sector + sizeof(BIOSParamBlock), sizeof(ExtBootRecord_32));
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} else { // FAT12 or 16
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fat->ebr = new ExtBootRecord_12_16;
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memcpy(fat->ebr, (char *)fat->sector + sizeof(BIOSParamBlock), sizeof(ExtBootRecord_12_16));
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// Let's tell FAT12 from FAT16
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// see fat12_fat16.txt
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// "For disks containing more than 4085 clusters (note that
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// 4085 is the correct number), a 16-bit FAT entry is used."
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//
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// Let's first try the name
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if (strncmp(fat->ebr->type, "FAT12", 5) == 0)
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fat->type = FAT12;
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else if (strncmp(fat->ebr->type, "FAT16", 5) == 0)
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fat->type = FAT16;
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// Try the number of clusters
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else {
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int clusters = fat->numSectors / fat->bpb->numSectorsPerCluster;
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if (fat->numSectors % fat->bpb->numSectorsPerCluster != 0)
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clusters++; // round up
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if (clusters > 4085)
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fat->type = FAT16;
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else
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fat->type = FAT12;
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}
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}
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// read the FAT
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return fat;
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}
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} // namespace filesystem
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} // namespace helos
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