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87 lines
2.8 KiB
C++
87 lines
2.8 KiB
C++
/*
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* Copyright (c) 2022, Undefine <undefine@undefine.pl>
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*
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* SPDX-License-Identifier: BSD-2-Clause
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*/
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#pragma once
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#include <AK/Types.h>
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namespace Kernel {
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// This structure represents the DOS 3.31 BIOS Partition Block.
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// While DOS 3.31 predates FAT verions 12/16/32 (the versions supported by this driver),
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// the fields in this block are common with the DOS 4 and DOS 7 BIOS Parameter blocks.
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// This structure will be followed by an "Extended BIOS Partition Block" (EBPB).
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//
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// The DOS 4 EBPB is *typically* used by FAT 12/16 file systems, while the DOS 7 EBPB
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// is *typically* used by FAT 32. _However_, any combination is possible, as the FAT
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// version is only determined by the number of clusters.
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//
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// Note that the DOS 4 and DOS 7 EBPB extensions are incompatible with each other
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// (contain fields in different orders and of different lenghts) and do not contain
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// an explicit indication to differentiate them.
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// This driver uses heuristics to identify the EBPB version (based on the signature bytes
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// and sector counts).
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// FIXME: Consider also using the MBR parition type field in the future.
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struct [[gnu::packed]] DOS3BIOSParameterBlock {
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u8 boot_jump[3];
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char oem_identifier[8];
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u16 bytes_per_sector; // Offset 0x0B -- beginning of DOS 3.31 BPB.
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u8 sectors_per_cluster;
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u16 reserved_sector_count;
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u8 fat_count;
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u16 root_directory_entry_count;
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u16 sector_count_16bit;
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u8 media_descriptor_type;
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u16 sectors_per_fat_16bit;
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u16 sectors_per_track;
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u16 head_count;
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u32 hidden_sector_count;
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u32 sector_count_32bit; // 0x020 -- end of DOS 3.31 BPB.
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};
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// 11 is the boot jump/OEM identifier prefix prior to the official BPB.
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static_assert(AssertSize<DOS3BIOSParameterBlock, 11 + 25>());
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struct [[gnu::packed]] DOS4BIOSParameterBlock {
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// Begins at sector offset 0x024.
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u8 drive_number; // 0x024
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u8 flags;
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u8 signature;
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u32 volume_id;
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char volume_label_string[11];
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char file_system_type[8];
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};
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static_assert(AssertSize<DOS4BIOSParameterBlock, 26>());
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struct [[gnu::packed]] DOS7BIOSParameterBlock {
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// Begins at sector offset 0x024.
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u32 sectors_per_fat_32bit; // 0x024
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u16 flags;
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u16 fat_version; // Expected value 0x2b2a.
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u32 root_directory_cluster;
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u16 fs_info_sector;
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u16 backup_boot_sector;
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u8 unused3[12];
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u8 drive_number;
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u8 unused4;
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u8 signature;
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u32 volume_id;
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char volume_label_string[11];
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char file_system_type[8];
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};
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static_assert(AssertSize<DOS7BIOSParameterBlock, 54>());
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struct [[gnu::packed]] FAT32FSInfo {
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u32 lead_signature;
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u8 unused1[480];
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u32 struct_signature;
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u32 last_known_free_cluster_count;
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u32 next_free_cluster_hint;
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u8 unused2[12];
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u32 trailing_signature;
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};
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static_assert(AssertSize<FAT32FSInfo, 512>());
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}
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