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Kernel: Move FAT structure definitions to Kernel/API

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We need to be able to include these definitions from userspace as the
upcoming mkfs.fat utility will depend on these.
This commit is contained in:
implicitfield 2024-02-08 20:39:13 +04:00 committed by Andrew Kaster
parent f2503b2048
commit 8b77737f8e
Notes: sideshowbarker 2024-07-16 23:57:20 +09:00 
Author: https://github.com/implicitfield
Commit: https://github.com/SerenityOS/serenity/commit/8b77737f8e
Pull-request: https://github.com/SerenityOS/serenity/pull/22810
Reviewed-by: https://github.com/ADKaster ✅
2 changed files with 77 additions and 63 deletions
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76
Kernel/API/FileSystem/FATStructures.h Normal file
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@ -0,0 +1,76 @@
/*
* Copyright (c) 2022, Undefine <undefine@undefine.pl>
*
* SPDX-License-Identifier: BSD-2-Clause
*/
#pragma once
#include <AK/Types.h>
namespace Kernel {
// This structure represents the DOS 3.31 BIOS Partition Block.
// While DOS 3.31 predates FAT verions 12/16/32 (the versions supported by this driver),
// the fields in this block are common with the DOS 4 and DOS 7 BIOS Parameter blocks.
// This structure will be followed by an "Extended BIOS Partition Block" (EBPB).
//
// The DOS 4 EBPB is *typically* used by FAT 12/16 file systems, while the DOS 7 EBPB
// is *typically* used by FAT 32. _However_, any combination is possible, as the FAT
// version is only determined by the number of clusters.
//
// Note that the DOS 4 and DOS 7 EBPB extensions are incompatible with each other
// (contain fields in different orders and of different lenghts) and do not contain
// an explicit indication to differentiate them.
// This driver uses heuristics to identify the EBPB version (based on the signature bytes
// and sector counts).
// FIXME: Consider also using the MBR parition type field in the future.
struct [[gnu::packed]] DOS3BIOSParameterBlock {
u8 boot_jump[3];
char oem_identifier[8];
u16 bytes_per_sector; // Offset 0x0B -- beginning of DOS 3.31 BPB.
u8 sectors_per_cluster;
u16 reserved_sector_count;
u8 fat_count;
u16 root_directory_entry_count;
u16 sector_count_16bit;
u8 media_descriptor_type;
u16 sectors_per_fat_16bit;
u16 sectors_per_track;
u16 head_count;
u32 hidden_sector_count;
u32 sector_count_32bit; // 0x020 -- end of DOS 3.31 BPB.
};
// 11 is the boot jump/OEM identifier prefix prior to the official BPB.
static_assert(AssertSize<DOS3BIOSParameterBlock, 11 + 25>());
struct [[gnu::packed]] DOS4BIOSParameterBlock {
// Begins at sector offset 0x024.
u8 drive_number; // 0x024
u8 flags;
u8 signature;
u32 volume_id;
char volume_label_string[11];
char file_system_type[8];
};
static_assert(AssertSize<DOS4BIOSParameterBlock, 26>());
struct [[gnu::packed]] DOS7BIOSParameterBlock {
// Begins at sector offset 0x024.
u32 sectors_per_fat_32bit; // 0x024
u16 flags;
u16 fat_version; // Expected value 0x2b2a.
u32 root_directory_cluster;
u16 fs_info_sector;
u16 backup_boot_sector;
u8 unused3[12];
u8 drive_number;
u8 unused4;
u8 signature;
u32 volume_id;
char volume_label_string[11];
char file_system_type[8];
};
static_assert(AssertSize<DOS7BIOSParameterBlock, 54>());
}

64
Kernel/FileSystem/FATFS/Definitions.h
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@ -9,73 +9,11 @@
#include <AK/DOSPackedTime.h>
#include <AK/EnumBits.h>
#include <AK/Types.h>
#include <Kernel/API/FileSystem/FATStructures.h>
#include <Kernel/Library/KBuffer.h>
namespace Kernel {
// This structure represents the DOS 3.31 BIOS Partition Block.
// While DOS 3.31 predates FAT verions 12/16/32 (the versions supported by this driver),
// the fields in this block are common with the DOS 4 and DOS 7 BIOS Parameter blocks.
// This structure will be followed by an "Extended BIOS Partition Block" (EBPB).
//
// The DOS 4 EBPB is *typically* used by FAT 12/16 file systems, while the DOS 7 EBPB
// is *typically* used by FAT 32. _However_, any combination is possible, as the FAT
// version is only determined by the number of clusters.
//
// Note that the DOS 4 and DOS 7 EBPB extensions are incompatible with each other
// (contain fields in different orders and of different lenghts) and do not contain
// an explicit indication to differentiate them.
// This driver uses heuristics to identify the EBPB version (based on the signature bytes
// and sector counts).
// FIXME: Consider also using the MBR parition type field in the future.
struct [[gnu::packed]] DOS3BIOSParameterBlock {
u8 boot_jump[3];
char oem_identifier[8];
u16 bytes_per_sector; // Offset 0x0B -- beginning of DOS 3.31 BPB.
u8 sectors_per_cluster;
u16 reserved_sector_count;
u8 fat_count;
u16 root_directory_entry_count;
u16 sector_count_16bit;
u8 media_descriptor_type;
u16 sectors_per_fat_16bit;
u16 sectors_per_track;
u16 head_count;
u32 hidden_sector_count;
u32 sector_count_32bit; // 0x020 -- end of DOS 3.31 BPB.
};
// 11 is the boot jump/OEM identifier prefix prior to the official BPB.
static_assert(AssertSize<DOS3BIOSParameterBlock, 11 + 25>());
struct [[gnu::packed]] DOS4BIOSParameterBlock {
// Begins at sector offset 0x024.
u8 drive_number; // 0x024
u8 flags;
u8 signature;
u32 volume_id;
char volume_label_string[11];
char file_system_type[8];
};
static_assert(AssertSize<DOS4BIOSParameterBlock, 26>());
struct [[gnu::packed]] DOS7BIOSParameterBlock {
// Begins at sector offset 0x024.
u32 sectors_per_fat_32bit; // 0x024
u16 flags;
u16 fat_version; // Expected value 0x2b2a.
u32 root_directory_cluster;
u16 fs_info_sector;
u16 backup_boot_sector;
u8 unused3[12];
u8 drive_number;
u8 unused4;
u8 signature;
u32 volume_id;
char volume_label_string[11];
char file_system_type[8];
};
static_assert(AssertSize<DOS7BIOSParameterBlock, 54>());
enum DOSBIOSParameterBlockVersion {
DOS_BPB_UNKNOWN,
DOS_BPB_3, // Version 3.4.