Kernel: Add support for the FAT32 filesystem

This commit adds read-only support for the FAT32 filesystem. It also
includes support for long file names.

Kernel/CMakeLists.txt

@@ -111,6 +111,7 @@ set(KERNEL_SOURCES
     FileSystem/DevPtsFS.cpp
     FileSystem/DevTmpFS.cpp
     FileSystem/Ext2FileSystem.cpp
+    FileSystem/FATFileSystem.cpp
     FileSystem/FIFO.cpp
     FileSystem/File.cpp
     FileSystem/FileBackedFileSystem.cpp

Kernel/Debug.h.in

@@ -91,6 +91,10 @@
 #cmakedefine01 EXT2_VERY_DEBUG
 #endif
 
+#ifndef FAT_DEBUG
+#cmakedefine01 FAT_DEBUG
+#endif
+
 #ifndef FRAMEBUFFER_DEVICE_DEBUG
 #cmakedefine01 FRAMEBUFFER_DEVICE_DEBUG
 #endif

Kernel/FileSystem/FATFileSystem.cpp

@@ -0,0 +1,348 @@
+/*
+ * Copyright (c) 2022, Undefine <undefine@undefine.pl>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include <AK/Time.h>
+#include <Kernel/Debug.h>
+#include <Kernel/Devices/BlockDevice.h>
+#include <Kernel/FileSystem/FATFileSystem.h>
+#include <Kernel/Memory/Region.h>
+
+namespace Kernel {
+
+ErrorOr<NonnullLockRefPtr<FileSystem>> FATFS::try_create(OpenFileDescription& file_description)
+{
+    return TRY(adopt_nonnull_lock_ref_or_enomem(new (nothrow) FATFS(file_description)));
+}
+
+FATFS::FATFS(OpenFileDescription& file_description)
+    : BlockBasedFileSystem(file_description)
+{
+}
+
+ErrorOr<void> FATFS::initialize()
+{
+    MutexLocker locker(m_lock);
+
+    m_boot_record = TRY(KBuffer::try_create_with_size("FATFS: Boot Record"sv, m_logical_block_size));
+    auto boot_record_buffer = UserOrKernelBuffer::for_kernel_buffer(m_boot_record->data());
+    TRY(raw_read(0, boot_record_buffer));
+
+    if constexpr (FAT_DEBUG) {
+        dbgln("FATFS: oem_identifier: {}", boot_record()->oem_identifier);
+        dbgln("FATFS: bytes_per_sector: {}", boot_record()->bytes_per_sector);
+        dbgln("FATFS: sectors_per_cluster: {}", boot_record()->sectors_per_cluster);
+        dbgln("FATFS: reserved_sector_count: {}", boot_record()->reserved_sector_count);
+        dbgln("FATFS: fat_count: {}", boot_record()->fat_count);
+        dbgln("FATFS: root_directory_entry_count: {}", boot_record()->root_directory_entry_count);
+        dbgln("FATFS: media_descriptor_type: {}", boot_record()->media_descriptor_type);
+        dbgln("FATFS: sectors_per_track: {}", boot_record()->sectors_per_track);
+        dbgln("FATFS: head_count: {}", boot_record()->head_count);
+        dbgln("FATFS: hidden_sector_count: {}", boot_record()->hidden_sector_count);
+        dbgln("FATFS: sector_count: {}", boot_record()->sector_count);
+        dbgln("FATFS: sectors_per_fat: {}", boot_record()->sectors_per_fat);
+        dbgln("FATFS: flags: {}", boot_record()->flags);
+        dbgln("FATFS: fat_version: {}", boot_record()->fat_version);
+        dbgln("FATFS: root_directory_cluster: {}", boot_record()->root_directory_cluster);
+        dbgln("FATFS: fs_info_sector: {}", boot_record()->fs_info_sector);
+        dbgln("FATFS: backup_boot_sector: {}", boot_record()->backup_boot_sector);
+        dbgln("FATFS: drive_number: {}", boot_record()->drive_number);
+        dbgln("FATFS: volume_id: {}", boot_record()->volume_id);
+    }
+
+    if (boot_record()->signature != signature_1 && boot_record()->signature != signature_2) {
+        dbgln("FATFS: Invalid signature");
+        return EINVAL;
+    }
+
+    m_logical_block_size = boot_record()->bytes_per_sector;
+    set_block_size(m_logical_block_size);
+
+    u32 root_directory_sectors = ((boot_record()->root_directory_entry_count * sizeof(FATEntry)) + (m_logical_block_size - 1)) / m_logical_block_size;
+    m_first_data_sector = boot_record()->reserved_sector_count + (boot_record()->fat_count * boot_record()->sectors_per_fat) + root_directory_sectors;
+
+    TRY(BlockBasedFileSystem::initialize());
+
+    FATEntry root_entry {};
+
+    root_entry.first_cluster_low = boot_record()->root_directory_cluster & 0xFFFF;
+    root_entry.first_cluster_high = boot_record()->root_directory_cluster >> 16;
+
+    root_entry.attributes = FATAttributes::Directory;
+    m_root_inode = TRY(FATInode::create(*this, root_entry));
+
+    return {};
+}
+
+Inode& FATFS::root_inode()
+{
+    return *m_root_inode;
+}
+
+BlockBasedFileSystem::BlockIndex FATFS::first_block_of_cluster(u32 cluster) const
+{
+    return ((cluster - first_data_cluster) * boot_record()->sectors_per_cluster) + m_first_data_sector;
+}
+
+ErrorOr<NonnullLockRefPtr<FATInode>> FATInode::create(FATFS& fs, FATEntry entry, Vector<FATLongFileNameEntry> const& lfn_entries)
+{
+    auto filename = TRY(compute_filename(entry, lfn_entries));
+    return adopt_nonnull_lock_ref_or_enomem(new (nothrow) FATInode(fs, entry, move(filename)));
+}
+
+FATInode::FATInode(FATFS& fs, FATEntry entry, NonnullOwnPtr<KString> filename)
+    : Inode(fs, first_cluster())
+    , m_entry(entry)
+    , m_filename(move(filename))
+{
+    dbgln_if(FAT_DEBUG, "FATFS: Creating inode {} with filename \"{}\"", index(), m_filename);
+
+    m_metadata = {
+        .inode = identifier(),
+        .size = m_entry.file_size,
+        .mode = static_cast<mode_t>((has_flag(m_entry.attributes, FATAttributes::Directory) ? S_IFDIR : S_IFREG) | 0777),
+        .uid = 0,
+        .gid = 0,
+        .link_count = 0,
+        .atime = fat_date_time(m_entry.last_accessed_date, { 0 }),
+        .ctime = fat_date_time(m_entry.creation_date, m_entry.creation_time),
+        .mtime = fat_date_time(m_entry.modification_date, m_entry.modification_time),
+        .dtime = 0,
+        .block_count = 0,
+        .block_size = 0,
+        .major_device = 0,
+        .minor_device = 0,
+    };
+}
+
+ErrorOr<Vector<BlockBasedFileSystem::BlockIndex>> FATInode::compute_block_list()
+{
+    VERIFY(m_inode_lock.is_locked());
+
+    dbgln_if(FAT_DEBUG, "FATFS: computing block list for inode {}", index());
+
+    u32 cluster = first_cluster();
+
+    Vector<BlockBasedFileSystem::BlockIndex> block_list;
+
+    auto fat_sector = TRY(KBuffer::try_create_with_size("FATFS: FAT read buffer"sv, fs().m_logical_block_size));
+    auto fat_sector_buffer = UserOrKernelBuffer::for_kernel_buffer(fat_sector->data());
+
+    while (cluster < no_more_clusters) {
+        dbgln_if(FAT_DEBUG, "FATFS: Appending cluster {} to inode {}'s cluster chain", cluster, index());
+
+        BlockBasedFileSystem::BlockIndex first_block = fs().first_block_of_cluster(cluster);
+        for (u8 i = 0; i < fs().boot_record()->sectors_per_cluster; i++)
+            block_list.append(BlockBasedFileSystem::BlockIndex { first_block.value() + i });
+
+        u32 fat_offset = cluster * sizeof(u32);
+        u32 fat_sector_index = fs().boot_record()->reserved_sector_count + (fat_offset / fs().m_logical_block_size);
+        u32 entry_offset = fat_offset % fs().m_logical_block_size;
+
+        TRY(fs().raw_read(fat_sector_index, fat_sector_buffer));
+
+        cluster = *reinterpret_cast<u32*>(&fat_sector->data()[entry_offset]);
+        cluster &= cluster_number_mask;
+    }
+
+    return block_list;
+}
+
+ErrorOr<NonnullOwnPtr<KBuffer>> FATInode::read_block_list()
+{
+    VERIFY(m_inode_lock.is_locked());
+
+    dbgln_if(FAT_DEBUG, "FATFS: reading block list for inode {} ({} blocks)", index(), m_block_list.size());
+
+    if (m_block_list.is_empty())
+        m_block_list = TRY(compute_block_list());
+
+    auto builder = TRY(KBufferBuilder::try_create());
+
+    u8 buffer[512];
+    VERIFY(fs().m_logical_block_size <= sizeof(buffer));
+    auto buf = UserOrKernelBuffer::for_kernel_buffer(buffer);
+
+    for (BlockBasedFileSystem::BlockIndex block : m_block_list) {
+        dbgln_if(FAT_DEBUG, "FATFS: reading block: {}", block);
+        TRY(fs().raw_read(block, buf));
+        TRY(builder.append((char const*)buffer, fs().m_logical_block_size));
+    }
+
+    auto blocks = builder.build();
+    if (!blocks)
+        return ENOMEM;
+    return blocks.release_nonnull();
+}
+
+ErrorOr<LockRefPtr<FATInode>> FATInode::traverse(Function<ErrorOr<bool>(LockRefPtr<FATInode>)> callback)
+{
+    VERIFY(has_flag(m_entry.attributes, FATAttributes::Directory));
+
+    Vector<FATLongFileNameEntry> lfn_entries;
+    auto blocks = TRY(read_block_list());
+
+    for (u32 i = 0; i < blocks->size() / sizeof(FATEntry); i++) {
+        auto* entry = reinterpret_cast<FATEntry*>(blocks->data() + i * sizeof(FATEntry));
+        if (entry->filename[0] == end_entry_byte) {
+            dbgln_if(FAT_DEBUG, "FATFS: Found end entry");
+            return nullptr;
+        } else if (static_cast<u8>(entry->filename[0]) == unused_entry_byte) {
+            dbgln_if(FAT_DEBUG, "FATFS: Found unused entry");
+            lfn_entries.clear();
+        } else if (entry->attributes == FATAttributes::LongFileName) {
+            dbgln_if(FAT_DEBUG, "FATFS: Found LFN entry");
+            TRY(lfn_entries.try_append(*reinterpret_cast<FATLongFileNameEntry*>(entry)));
+        } else {
+            dbgln_if(FAT_DEBUG, "FATFS: Found 8.3 entry");
+            lfn_entries.reverse();
+            auto inode = TRY(FATInode::create(fs(), *entry, lfn_entries));
+            if (TRY(callback(inode)))
+                return inode;
+            lfn_entries.clear();
+        }
+    }
+
+    return EINVAL;
+}
+
+ErrorOr<NonnullOwnPtr<KString>> FATInode::compute_filename(FATEntry& entry, Vector<FATLongFileNameEntry> const& lfn_entries)
+{
+    if (lfn_entries.is_empty()) {
+        StringBuilder filename;
+        filename.append(byte_terminated_string(StringView(entry.filename, normal_filename_length), ' '));
+        if (entry.extension[0] != ' ') {
+            filename.append('.');
+            filename.append(byte_terminated_string(StringView(entry.extension, normal_extension_length), ' '));
+        }
+        return TRY(KString::try_create(filename.string_view()));
+    } else {
+        StringBuilder filename;
+        for (auto& lfn_entry : lfn_entries) {
+            filename.append(lfn_entry.characters1[0]);
+            filename.append(lfn_entry.characters1[1]);
+            filename.append(lfn_entry.characters1[2]);
+            filename.append(lfn_entry.characters1[3]);
+            filename.append(lfn_entry.characters1[4]);
+            filename.append(lfn_entry.characters2[0]);
+            filename.append(lfn_entry.characters2[1]);
+            filename.append(lfn_entry.characters2[2]);
+            filename.append(lfn_entry.characters2[3]);
+            filename.append(lfn_entry.characters2[4]);
+            filename.append(lfn_entry.characters2[5]);
+            filename.append(lfn_entry.characters3[0]);
+            filename.append(lfn_entry.characters3[1]);
+        }
+
+        return TRY(KString::try_create(byte_terminated_string(filename.string_view(), lfn_entry_text_termination)));
+    }
+
+    VERIFY_NOT_REACHED();
+}
+
+time_t FATInode::fat_date_time(FATPackedDate date, FATPackedTime time)
+{
+    if (date.value == 0)
+        return 0;
+
+    return Time::from_timestamp(first_fat_year + date.year, date.month, date.day, time.hour, time.minute, time.second * 2, 0).to_seconds();
+}
+
+StringView FATInode::byte_terminated_string(StringView string, u8 fill_byte)
+{
+    if (auto index = string.find_last_not(fill_byte); index.has_value())
+        return string.substring_view(0, index.value());
+    return string;
+}
+
+u32 FATInode::first_cluster() const
+{
+    return (((u32)m_entry.first_cluster_high) << 16) | m_entry.first_cluster_low;
+}
+
+ErrorOr<size_t> FATInode::read_bytes_locked(off_t offset, size_t size, UserOrKernelBuffer& buffer, OpenFileDescription*) const
+{
+    dbgln_if(FAT_DEBUG, "FATFS: Reading inode {}: size: {} offset: {}", identifier().index(), size, offset);
+
+    // FIXME: Read only the needed blocks instead of the whole file
+    auto blocks = TRY(const_cast<FATInode&>(*this).read_block_list());
+    TRY(buffer.write(blocks->data() + offset, min(size, m_block_list.size() * fs().m_logical_block_size - offset)));
+
+    return min(size, m_block_list.size() * fs().m_logical_block_size - offset);
+}
+
+InodeMetadata FATInode::metadata() const
+{
+    return m_metadata;
+}
+
+ErrorOr<void> FATInode::traverse_as_directory(Function<ErrorOr<void>(FileSystem::DirectoryEntryView const&)> callback) const
+{
+    MutexLocker locker(m_inode_lock);
+
+    VERIFY(has_flag(m_entry.attributes, FATAttributes::Directory));
+
+    [[maybe_unused]] auto inode = TRY(const_cast<FATInode&>(*this).traverse([&callback](auto inode) -> ErrorOr<bool> {
+        if (inode->m_filename->view() == "" || inode->m_filename->view() == "." || inode->m_filename->view() == "..")
+            return false;
+        TRY(callback({ inode->m_filename->view(), inode->identifier(), static_cast<u8>(inode->m_entry.attributes) }));
+        return false;
+    }));
+
+    return {};
+}
+
+ErrorOr<NonnullLockRefPtr<Inode>> FATInode::lookup(StringView name)
+{
+    MutexLocker locker(m_inode_lock);
+
+    VERIFY(has_flag(m_entry.attributes, FATAttributes::Directory));
+
+    auto inode = TRY(traverse([name](auto child) -> ErrorOr<bool> {
+        return child->m_filename->view() == name;
+    }));
+
+    if (inode.is_null())
+        return ENOENT;
+    else
+        return inode.release_nonnull();
+}
+
+ErrorOr<size_t> FATInode::write_bytes_locked(off_t, size_t, UserOrKernelBuffer const&, OpenFileDescription*)
+{
+    return EROFS;
+}
+
+ErrorOr<NonnullLockRefPtr<Inode>> FATInode::create_child(StringView, mode_t, dev_t, UserID, GroupID)
+{
+    return EROFS;
+}
+
+ErrorOr<void> FATInode::add_child(Inode&, StringView, mode_t)
+{
+    return EROFS;
+}
+
+ErrorOr<void> FATInode::remove_child(StringView)
+{
+    return EROFS;
+}
+
+ErrorOr<void> FATInode::chmod(mode_t)
+{
+    return EROFS;
+}
+
+ErrorOr<void> FATInode::chown(UserID, GroupID)
+{
+    return EROFS;
+}
+
+ErrorOr<void> FATInode::flush_metadata()
+{
+    return EROFS;
+}
+
+}

Kernel/FileSystem/FATFileSystem.h

@@ -0,0 +1,196 @@
+/*
+ * Copyright (c) 2022, Undefine <undefine@undefine.pl>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include <AK/OwnPtr.h>
+#include <AK/RefPtr.h>
+#include <AK/Types.h>
+#include <Kernel/FileSystem/BlockBasedFileSystem.h>
+#include <Kernel/FileSystem/Inode.h>
+#include <Kernel/KBuffer.h>
+
+namespace Kernel {
+
+struct [[gnu::packed]] FAT32BootRecord {
+    u8 boot_jump[3];
+    char oem_identifier[8];
+    u16 bytes_per_sector;
+    u8 sectors_per_cluster;
+    u16 reserved_sector_count;
+    u8 fat_count;
+    u16 root_directory_entry_count;
+    u16 unused1;
+    u8 media_descriptor_type;
+    u16 unused2;
+    u16 sectors_per_track;
+    u16 head_count;
+    u32 hidden_sector_count;
+    u32 sector_count;
+    u32 sectors_per_fat;
+    u16 flags;
+    u16 fat_version;
+    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 system_identifier_string[8];
+};
+static_assert(sizeof(FAT32BootRecord) == 90);
+
+enum class FATAttributes : u8 {
+    ReadOnly = 0x01,
+    Hidden = 0x02,
+    System = 0x04,
+    VolumeID = 0x08,
+    Directory = 0x10,
+    Archive = 0x20,
+    LongFileName = 0x0F
+};
+
+AK_ENUM_BITWISE_OPERATORS(FATAttributes);
+
+union FATPackedTime {
+    u16 value;
+    struct {
+        u16 second : 5;
+        u16 minute : 6;
+        u16 hour : 5;
+    };
+};
+static_assert(sizeof(FATPackedTime) == 2);
+
+union FATPackedDate {
+    u16 value;
+    struct {
+        u16 day : 5;
+        u16 month : 4;
+        u16 year : 7;
+    };
+};
+static_assert(sizeof(FATPackedDate) == 2);
+
+struct [[gnu::packed]] FATEntry {
+    char filename[8];
+    char extension[3];
+    FATAttributes attributes;
+    u8 unused1;
+    u8 creation_time_seconds;
+    FATPackedTime creation_time;
+    FATPackedDate creation_date;
+    FATPackedDate last_accessed_date;
+    u16 first_cluster_high;
+    FATPackedTime modification_time;
+    FATPackedDate modification_date;
+    u16 first_cluster_low;
+    u32 file_size;
+};
+static_assert(sizeof(FATEntry) == 32);
+
+struct [[gnu::packed]] FATLongFileNameEntry {
+    u8 entry_index;
+    u16 characters1[5];
+    FATAttributes attributes;
+    u8 entry_type;
+    u8 checksum;
+    u16 characters2[6];
+    u16 zero;
+    u16 characters3[2];
+};
+static_assert(sizeof(FATLongFileNameEntry) == 32);
+
+class FATInode;
+
+class FATFS final : public BlockBasedFileSystem {
+    friend FATInode;
+
+public:
+    static ErrorOr<NonnullLockRefPtr<FileSystem>> try_create(OpenFileDescription&);
+
+    virtual ~FATFS() override = default;
+    virtual ErrorOr<void> initialize() override;
+    virtual StringView class_name() const override { return "FATFS"sv; }
+    virtual Inode& root_inode() override;
+
+private:
+    FATFS(OpenFileDescription&);
+
+    static constexpr u8 signature_1 = 0x28;
+    static constexpr u8 signature_2 = 0x29;
+
+    static constexpr u32 first_data_cluster = 2;
+
+    FAT32BootRecord const* boot_record() const { return reinterpret_cast<FAT32BootRecord const*>(m_boot_record->data()); };
+
+    BlockBasedFileSystem::BlockIndex first_block_of_cluster(u32 cluster) const;
+
+    OwnPtr<KBuffer> m_boot_record;
+    LockRefPtr<FATInode> m_root_inode;
+    u32 m_first_data_sector;
+};
+
+class FATInode final : public Inode {
+    friend FATFS;
+
+public:
+    virtual ~FATInode() override = default;
+
+    static ErrorOr<NonnullLockRefPtr<FATInode>> create(FATFS&, FATEntry, Vector<FATLongFileNameEntry> const& = {});
+
+    FATFS& fs() { return static_cast<FATFS&>(Inode::fs()); }
+    FATFS const& fs() const { return static_cast<FATFS const&>(Inode::fs()); }
+
+private:
+    FATInode(FATFS&, FATEntry, NonnullOwnPtr<KString> filename);
+
+    static constexpr u32 no_more_clusters = 0x0FFFFFF8;
+    static constexpr u32 cluster_number_mask = 0x0FFFFFFF;
+
+    static constexpr u8 end_entry_byte = 0x00;
+    static constexpr u8 unused_entry_byte = 0xE5;
+
+    static constexpr u8 lfn_entry_text_termination = 0xFF;
+
+    static constexpr u16 first_fat_year = 1980;
+
+    static constexpr u8 normal_filename_length = 8;
+    static constexpr u8 normal_extension_length = 3;
+
+    static ErrorOr<NonnullOwnPtr<KString>> compute_filename(FATEntry&, Vector<FATLongFileNameEntry> const& = {});
+    static StringView byte_terminated_string(StringView, u8);
+    static time_t fat_date_time(FATPackedDate date, FATPackedTime time);
+
+    ErrorOr<Vector<BlockBasedFileSystem::BlockIndex>> compute_block_list();
+    ErrorOr<NonnullOwnPtr<KBuffer>> read_block_list();
+    ErrorOr<LockRefPtr<FATInode>> traverse(Function<ErrorOr<bool>(LockRefPtr<FATInode>)> callback);
+    u32 first_cluster() const;
+
+    // ^Inode
+    virtual ErrorOr<size_t> write_bytes_locked(off_t, size_t, UserOrKernelBuffer const& data, OpenFileDescription*) override;
+    virtual ErrorOr<size_t> read_bytes_locked(off_t, size_t, UserOrKernelBuffer& buffer, OpenFileDescription*) const override;
+
+    virtual InodeMetadata metadata() const override;
+    virtual ErrorOr<void> traverse_as_directory(Function<ErrorOr<void>(FileSystem::DirectoryEntryView const&)>) const override;
+    virtual ErrorOr<NonnullLockRefPtr<Inode>> lookup(StringView name) override;
+    virtual ErrorOr<NonnullLockRefPtr<Inode>> create_child(StringView name, mode_t, dev_t, UserID, GroupID) override;
+    virtual ErrorOr<void> add_child(Inode&, StringView name, mode_t) override;
+    virtual ErrorOr<void> remove_child(StringView name) override;
+    virtual ErrorOr<void> chmod(mode_t) override;
+    virtual ErrorOr<void> chown(UserID, GroupID) override;
+    virtual ErrorOr<void> flush_metadata() override;
+
+    Vector<BlockBasedFileSystem::BlockIndex> m_block_list;
+    FATEntry m_entry;
+    NonnullOwnPtr<KString> m_filename;
+    InodeMetadata m_metadata;
+};
+
+}

Kernel/Syscalls/mount.cpp

@@ -8,6 +8,7 @@
 #include <Kernel/FileSystem/DevPtsFS.h>
 #include <Kernel/FileSystem/DevTmpFS.h>
 #include <Kernel/FileSystem/Ext2FileSystem.h>
+#include <Kernel/FileSystem/FATFileSystem.h>
 #include <Kernel/FileSystem/ISO9660FileSystem.h>
 #include <Kernel/FileSystem/Plan9FileSystem.h>
 #include <Kernel/FileSystem/ProcFS.h>
@@ -37,6 +38,7 @@ static constexpr FileSystemInitializer s_initializers[] = {
     { "ext2"sv, "Ext2FS"sv, true, true, true, Ext2FS::try_create, {} },
     { "9p"sv, "Plan9FS"sv, true, true, true, Plan9FS::try_create, {} },
     { "iso9660"sv, "ISO9660FS"sv, true, true, true, ISO9660FS::try_create, {} },
+    { "fat"sv, "FATFS"sv, true, true, true, FATFS::try_create, {} },
 };
 
 static ErrorOr<NonnullLockRefPtr<FileSystem>> create_filesystem_instance(StringView fs_type, OpenFileDescription* possible_description)

Meta/CMake/all_the_debug_macros.cmake

@@ -53,6 +53,7 @@ set(EXEC_DEBUG ON)
 set(EXT2_BLOCKLIST_DEBUG ON)
 set(EXT2_DEBUG ON)
 set(EXT2_VERY_DEBUG ON)
+set(FAT_DEBUG ON)
 set(FILE_CONTENT_DEBUG ON)
 set(FILEDESCRIPTION_DEBUG ON)
 set(FILE_WATCHER_DEBUG ON)