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Kernel: Implement read-only FAT12/16/32 driver with long name support

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You can now mount FAT filesystems! This code might not work perfectly
but my quick testing seemed to work on all (FAT12/16/32) variants.
This commit is contained in:
Bananymous
2024-06-14 01:02:28 +03:00
parent 6b1d5d28be
commit ea7fc7f6c4
8 changed files with 864 additions and 0 deletions
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72
kernel/include/kernel/FS/FAT/FileSystem.h Normal file
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#pragma once
#include <BAN/HashMap.h>
#include <kernel/FS/FAT/Definitions.h>
#include <kernel/FS/FAT/Inode.h>
#include <kernel/FS/FileSystem.h>
namespace Kernel
{
class FATFS final : public FileSystem
{
public:
enum class Type
{
FAT12 = 12,
FAT16 = 16,
FAT32 = 32,
};
public:
static BAN::ErrorOr<bool> probe(BAN::RefPtr<BlockDevice>);
static BAN::ErrorOr<BAN::RefPtr<FATFS>> create(BAN::RefPtr<BlockDevice>);
virtual BAN::RefPtr<Inode> root_inode() override { return m_root_inode; }
virtual dev_t dev() const override { return m_block_device->rdev(); };
BAN::ErrorOr<BAN::RefPtr<FATInode>> open_inode(BAN::RefPtr<FATInode> parent, const FAT::DirectoryEntry& entry, uint32_t cluster_index, uint32_t entry_index);
BAN::ErrorOr<void> inode_read_cluster(BAN::RefPtr<FATInode>, size_t index, BAN::ByteSpan buffer);
blksize_t inode_block_size(BAN::RefPtr<const FATInode>) const;
private:
FATFS(BAN::RefPtr<BlockDevice> block_device, FAT::BPB bpb)
: m_block_device(block_device)
, m_bpb(bpb)
, m_type((cluster_count() < 4085) ? Type::FAT12 : (cluster_count() < 65525) ? Type::FAT16 : Type::FAT32)
{}
static bool validate_bpb(const FAT::BPB&);
BAN::ErrorOr<void> initialize();
BAN::ErrorOr<void> fat_cache_set_sector(uint32_t sector);
BAN::ErrorOr<uint32_t> get_next_cluster(uint32_t cluster);
// TODO: These probably should be constant variables
uint32_t root_sector_count() const { return BAN::Math::div_round_up<uint32_t>(m_bpb.root_entry_count * 32, m_bpb.bytes_per_sector); }
uint32_t fat_sector_count() const { return m_bpb.fat_size16 ? m_bpb.fat_size16 : m_bpb.ext_32.fat_size32; }
uint32_t total_sector_count() const { return m_bpb.total_sectors16 ? m_bpb.total_sectors16 : m_bpb.total_sectors32; }
uint32_t data_sector_count() const { return total_sector_count() - (m_bpb.reserved_sector_count + (m_bpb.number_of_fats * fat_sector_count()) + root_sector_count()); }
uint32_t cluster_count() const { return data_sector_count() / m_bpb.sectors_per_cluster; }
uint32_t first_data_sector() const { return m_bpb.reserved_sector_count + (m_bpb.number_of_fats * fat_sector_count()) + root_sector_count(); }
uint32_t first_fat_sector() const { return m_bpb.reserved_sector_count; }
private:
const FAT::BPB m_bpb;
const Type m_type;
BAN::RefPtr<BlockDevice> m_block_device;
BAN::RefPtr<FATInode> m_root_inode;
BAN::HashMap<ino_t, BAN::WeakPtr<FATInode>> m_inode_cache;
BAN::Vector<uint8_t> m_fat_two_sector_buffer;
uint32_t m_fat_sector_buffer_current { 0 };
Mutex m_mutex;
friend class BAN::RefPtr<FATFS>;
};
}