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ladybird/Kernel/FileSystem/FATFS/FileSystem.cpp

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/*
* Copyright (c) 2022-2024, Undefine <undefine@undefine.pl>
*
* SPDX-License-Identifier: BSD-2-Clause
*/
#include <AK/ByteReader.h>
#include <AK/Endian.h>
#include <Kernel/Debug.h>
#include <Kernel/FileSystem/FATFS/FileSystem.h>
#include <Kernel/FileSystem/FATFS/Inode.h>
namespace Kernel {
DOSBIOSParameterBlockVersion DOSBIOSParameterBlock::bpb_version() const
{
bool dos3_valid = m_dos4_block->signature == 0x28;
bool dos4_valid = m_dos4_block->signature == 0x29;
bool dos7_valid = m_dos7_block->signature == 0x28 || m_dos7_block->signature == 0x29;
// A DOS 7 EBPB should _never_ contain the values 0x28 or 0x29 at
// the offset associated with `m_dos4_block->signature`
// (aka `m_dos7_block->sectors_per_fat_32bit`) due to the maximum number of
// clusters ensuring the number of sectors per fat will not exceed 0x200000.
// As a result, it should be safe to determine BPB version through the
// signature fields by checking the DOS 4 signature offset prior to the DOS 7 one.
//
// With a DOS 3 or DOS 4 EBPB, the DOS 7 signature offset references uninitialized
// space. While unlikely to be set to a valid signature value, it is not implausible.
// We warn the user here, but because it does not represent an invalid FS configuration,
// do not error.
if ((dos3_valid || dos4_valid) && dos7_valid)
dbgln("FATFS: DOS 4 and DOS 7 EBPB signatures detected, EBPB/FAT version detection may be incorrect.");
if (dos3_valid)
return DOS_BPB_3;
else if (dos4_valid)
return DOS_BPB_4;
else if (dos7_valid)
return DOS_BPB_7;
else
return DOS_BPB_UNKNOWN;
}
DOS3BIOSParameterBlock const* DOSBIOSParameterBlock::common_bpb() const
{
return m_common_block;
}
DOS4BIOSParameterBlock const* DOSBIOSParameterBlock::dos4_bpb() const
{
// Only return parameter block if signature indicates this portion of the block is filled out.
if (m_dos4_block->signature == 0x28 || m_dos4_block->signature == 0x29)
return m_dos4_block;
else
return nullptr;
}
DOS7BIOSParameterBlock const* DOSBIOSParameterBlock::dos7_bpb() const
{
// Only return parameter block if signature indicates this portion of the block is filled out.
if (m_dos7_block->signature == 0x28 || m_dos7_block->signature == 0x29)
return m_dos7_block;
else
return nullptr;
}
u16 DOSBIOSParameterBlock::sectors_per_fat() const
{
return common_bpb()->sectors_per_fat_16bit != 0 ? common_bpb()->sectors_per_fat_16bit : m_dos7_block->sectors_per_fat_32bit;
}
u32 DOSBIOSParameterBlock::sector_count() const
{
if (common_bpb()->sector_count_16bit != 0) {
// The `16bit` field is only used on partitions smaller than 32 MB,
// and never for FAT32.
// It is set to `0` when the 32 bit field contains the sector count.
return common_bpb()->sector_count_16bit;
} else {
return common_bpb()->sector_count_32bit;
// FIXME: If this is 0 for a FAT32 EBPB with a signature of 0x29,
// read 0x052, which is a 64-bit wide sector count.
}
}
u8 DOSBIOSParameterBlock::signature() const
{
if (bpb_version() == DOS_BPB_3 || bpb_version() == DOS_BPB_4)
return m_dos4_block->signature;
else
return m_dos7_block->signature;
}
ErrorOr<NonnullRefPtr<FileSystem>> FATFS::try_create(OpenFileDescription& file_description, ReadonlyBytes)
{
return TRY(adopt_nonnull_ref_or_enomem(new (nothrow) FATFS(file_description)));
}
FATFS::FATFS(OpenFileDescription& file_description)
: BlockBasedFileSystem(file_description)
{
}
bool FATFS::is_initialized_while_locked()
{
VERIFY(m_lock.is_locked());
return !m_root_inode.is_null();
}
ErrorOr<void> FATFS::initialize_while_locked()
{
VERIFY(m_lock.is_locked());
VERIFY(!is_initialized_while_locked());
m_boot_record = TRY(KBuffer::try_create_with_size("FATFS: Boot Record"sv, m_device_block_size));
auto boot_record_buffer = UserOrKernelBuffer::for_kernel_buffer(m_boot_record->data());
TRY(raw_read(0, boot_record_buffer));
m_parameter_block = TRY(adopt_nonnull_own_or_enomem(new (nothrow) DOSBIOSParameterBlock(m_boot_record)));
// Alias for extended BPB.
DOSBIOSParameterBlock& ebpb = *m_parameter_block;
// Alias for block of common parameters in BPB.
DOS3BIOSParameterBlock const* block = ebpb.common_bpb();
if constexpr (FAT_DEBUG) {
dbgln("FATFS: oem_identifier: {}", block->oem_identifier);
dbgln("FATFS: bytes_per_sector: {}", static_cast<u16>(block->bytes_per_sector));
dbgln("FATFS: sectors_per_cluster: {}", block->sectors_per_cluster);
dbgln("FATFS: reserved_sector_count: {}", block->reserved_sector_count);
dbgln("FATFS: fat_count: {}", block->fat_count);
dbgln("FATFS: root_directory_entry_count: {}", static_cast<u16>(block->root_directory_entry_count));
dbgln("FATFS: media_descriptor_type: {}", block->media_descriptor_type);
dbgln("FATFS: sectors_per_track: {}", block->sectors_per_track);
dbgln("FATFS: head_count: {}", block->head_count);
dbgln("FATFS: hidden_sector_count: {}", block->hidden_sector_count);
dbgln("FATFS: sector_count: {}", ebpb.sector_count());
dbgln("FATFS: sectors_per_fat: {}", ebpb.sectors_per_fat());
auto ebpb_version = ebpb.bpb_version();
if (ebpb_version == DOSBIOSParameterBlockVersion::DOS_BPB_7) {
DOS7BIOSParameterBlock const* dos7_boot_record = ebpb.dos7_bpb();
dbgln("FATFS: EBPB: DOS 7");
dbgln("FATFS: flags: {}", dos7_boot_record->flags);
dbgln("FATFS: fat_version: {}", dos7_boot_record->fat_version);
dbgln("FATFS: root_directory_cluster: {}", dos7_boot_record->root_directory_cluster);
dbgln("FATFS: fs_info_sector: {}", dos7_boot_record->fs_info_sector);
dbgln("FATFS: backup_boot_sector: {}", dos7_boot_record->backup_boot_sector);
dbgln("FATFS: drive_number: {}", dos7_boot_record->drive_number);
dbgln("FATFS: volume_id: {}", static_cast<u32>(dos7_boot_record->volume_id));
} else if (ebpb_version == DOSBIOSParameterBlockVersion::DOS_BPB_3 || ebpb_version == DOSBIOSParameterBlockVersion::DOS_BPB_4) {
DOS4BIOSParameterBlock const* dos4_boot_record = ebpb.dos4_bpb();
if (ebpb_version == DOSBIOSParameterBlockVersion::DOS_BPB_3) {
dbgln("FATFS: EBPB: DOS 3.4");
} else if (ebpb_version == DOSBIOSParameterBlockVersion::DOS_BPB_4) {
dbgln("FATFS: EBPB: DOS 4");
}
dbgln("FATFS: drive_number: {}", dos4_boot_record->drive_number);
dbgln("FATFS: flags: {}", dos4_boot_record->flags);
dbgln("FATFS: volume_id: {}", static_cast<u32>(dos4_boot_record->volume_id));
// volume_label_string and file_system_type are only valid when
// ebpb_version == DOSBIOSParameterBlockVersion::DOS4.
}
}
if (ebpb.signature() != signature_1 && ebpb.signature() != signature_2) {
dbgln("FATFS: Invalid signature");
return EINVAL;
}
DOS3BIOSParameterBlock const* ebpb_block = ebpb.common_bpb();
// The number of data area sectors is what DOS/Windows used to determine
// if a partition was a FAT12, FAT16, or FAT32 file system.
// From "FAT Type Determination" section of Microsoft FAT Specification
// (fatgen103.doc):
// The FAT type—one of FAT12, FAT16, or FAT32—is determined by the count
// of clusters on the volume and nothing else.
//
// The following calculations are based on the equations provided in this
// section.
// "RootDirSectors" from MS FAT Specification. This is calculated as:
// Number of bytes occupied by root directory area (0 on FAT32)
// +
// Bytes to fill final sector (ie, round up)
// Converted into sector count (by dividing by bytes per sector).
u32 root_directory_sectors = ((ebpb_block->root_directory_entry_count * sizeof(FATEntry)) + (ebpb_block->bytes_per_sector - 1)) / ebpb_block->bytes_per_sector;
// "DataSec" from MS FAT Specification.
u32 data_area_sectors = ebpb.sector_count() - ((ebpb_block->reserved_sector_count) + (ebpb_block->fat_count * ebpb.sectors_per_fat()) + root_directory_sectors);
// CountofClusters from MS FAT Specification.
u32 data_area_clusters = data_area_sectors / ebpb_block->sectors_per_cluster;
// Cluster thresholds and operators as defined in MS FAT Specification.
if (data_area_clusters < 4085) {
dbgln("FATFS: Detected FAT12 with {} data area clusters", data_area_clusters);
m_fat_version = FATVersion::FAT12;
} else if (data_area_clusters < 65525) {
dbgln("FATFS: Detected FAT16 with {} data area clusters", data_area_clusters);
m_fat_version = FATVersion::FAT16;
} else {
dbgln("FATFS: Assuming FAT32 with {} data area clusters", data_area_clusters);
m_fat_version = FATVersion::FAT32;
}
m_device_block_size = ebpb_block->bytes_per_sector;
set_logical_block_size(m_device_block_size);
m_first_data_sector = block->reserved_sector_count + (block->fat_count * ebpb.sectors_per_fat()) + root_directory_sectors;
TRY(BlockBasedFileSystem::initialize_while_locked());
FATEntry root_entry {};
if (m_fat_version == FATVersion::FAT32) {
// FAT32 stores the root directory within the FAT (at the clusters specified
// in the boot record), as opposed to the root directory area
// (as done by FAT 12/16).
DOS7BIOSParameterBlock const* boot_record = ebpb.dos7_bpb();
// Ensure we have a DOS7 BPB (so that we can find the root directory cluster).
if (boot_record == nullptr) {
dbgln("FATFS: Non-DOS7 BPB for FAT32 FS.");
return EINVAL;
}
root_entry.first_cluster_low = boot_record->root_directory_cluster & 0xFFFF;
root_entry.first_cluster_high = boot_record->root_directory_cluster >> 16;
} else {
// FAT12/FAT16.
// Use cluster = 0 as a signal to `first_block_of_cluster()` to look in the
// root directory area for the root entry.
// Clusters 0 and 1 hold special values, and will never be used to store file
// data.
root_entry.first_cluster_low = 0;
root_entry.first_cluster_high = 0;
}
root_entry.attributes = FATAttributes::Directory;
m_root_inode = TRY(FATInode::create(*this, root_entry, { 0, 1 }));
if (m_fat_version == FATVersion::FAT32) {
auto fs_info_buffer = UserOrKernelBuffer::for_kernel_buffer(bit_cast<u8*>(&m_fs_info));
// We know that there is a DOS7 BPB, because if it wasn't present
// we would have returned EINVAL above.
TRY(read_block(ebpb.dos7_bpb()->fs_info_sector, &fs_info_buffer, sizeof(m_fs_info)));
if (m_fs_info.lead_signature != fs_info_signature_1 || m_fs_info.struct_signature != fs_info_signature_2 || m_fs_info.trailing_signature != fs_info_signature_3) {
dbgln("FATFS: Invalid FSInfo struct signature");
dbgln_if(FAT_DEBUG, "FATFS: FSInfo signature1: {:#x}, expected: {:#x}", m_fs_info.lead_signature, fs_info_signature_1);
dbgln_if(FAT_DEBUG, "FATFS: FSInfo signature2: {:#x}, expected: {:#x}", m_fs_info.struct_signature, fs_info_signature_2);
dbgln_if(FAT_DEBUG, "FATFS: FSInfo signature3: {:#x}, expected: {:#x}", m_fs_info.trailing_signature, fs_info_signature_3);
return Error::from_errno(EINVAL);
}
dbgln_if(FAT_DEBUG, "FATFS: fs_info.last_known_free_cluster_count: {}", m_fs_info.last_known_free_cluster_count);
dbgln_if(FAT_DEBUG, "FATFS: fs_info.next_free_cluster_hint: {}", m_fs_info.next_free_cluster_hint);
}
return {};
}
Inode& FATFS::root_inode()
{
return *m_root_inode;
}
FatBlockSpan FATFS::first_block_of_cluster(u32 cluster) const
{
// For FAT12/16, we use a value of cluster 0 to indicate this is a cluster for the root directory.
// Cluster 0 and cluster 1 hold special values (cluster 0 holds the FAT ID, and cluster 1
// the "end of chain marker"), neither of which will be present in the table or associated
// with any file.
// "Entries with the Volume Label flag, subdirectory ".." pointing to the FAT12 and FAT16 root, and empty files with size 0 should have first cluster 0."
// --Wikipedia
//
DOSBIOSParameterBlock ebpb(m_boot_record);
DOS3BIOSParameterBlock const* ebpb_block = ebpb.common_bpb();
if (m_fat_version != FATVersion::FAT32 && cluster == 0) {
// Root directory area follows the FATs after the reserved sectors.
return FatBlockSpan {
ebpb_block->reserved_sector_count + (ebpb_block->fat_count * ebpb.sectors_per_fat()),
(ebpb_block->root_directory_entry_count * sizeof(FATEntry)) / ebpb_block->bytes_per_sector
};
} else {
return FatBlockSpan {
((cluster - first_data_cluster) * ebpb_block->sectors_per_cluster) + m_first_data_sector,
ebpb_block->sectors_per_cluster
};
}
}
size_t FATFS::fat_offset_for_cluster(u32 cluster) const
{
switch (m_fat_version) {
case FATVersion::FAT12: {
// In FAT12, a cluster entry is stored in a byte, plus
// the low/high nibble of an adjacent byte.
//
// CLSTR: 0 1 2 3 4 5
// INDEX: [0 1 2], [3 4 5], [6 7 8]
// Every 2 clusters are represented using 3 bytes.
return (cluster * 3) / 2;
} break;
case FATVersion::FAT16:
return cluster * 2; // Each cluster is stored in 2 bytes.
case FATVersion::FAT32:
return cluster * 4; // Each cluster is stored in 4 bytes.
default:
VERIFY_NOT_REACHED();
}
}
u32 FATFS::cluster_number(KBuffer const& fat_sector, u32 entry_cluster_number, u32 entry_offset) const
{
u32 cluster = 0;
switch (m_fat_version) {
case FATVersion::FAT12: {
u16 fat12_bytes_le = 0;
// Two FAT12 entries get stored in a total of 3 bytes, as follows:
// AB CD EF are grouped as [D AB] and [E FC] (little-endian).
// For a given cluster, we interpret the associated 2 bytes as a little-endian
// 16-bit value ({CD AB} or {EF CD}), and then shift/mask the extra high or low nibble.
ByteReader::load<u16>(fat_sector.bytes().offset(entry_offset), fat12_bytes_le);
cluster = AK::convert_between_host_and_little_endian(fat12_bytes_le);
if (entry_cluster_number % 2 == 0) {
// CD AB -> D AB
cluster &= 0x0FFF;
} else {
// EF CD -> E FC.
cluster = cluster >> 4;
}
break;
}
case FATVersion::FAT16: {
u16 cluster_u16_le = 0;
ByteReader::load<u16>(fat_sector.bytes().offset(entry_offset), cluster_u16_le);
cluster = AK::convert_between_host_and_little_endian(cluster_u16_le);
break;
}
case FATVersion::FAT32: {
u32 cluster_u32_le = 0;
ByteReader::load<u32>(fat_sector.bytes().offset(entry_offset), cluster_u32_le);
cluster = AK::convert_between_host_and_little_endian(cluster_u32_le);
// FAT32 entries use 28-bits to represent the cluster number. The top 4 bits
// may contain flags or other data and must be masked off.
cluster &= 0x0FFFFFFF;
break;
}
default:
VERIFY_NOT_REACHED();
}
return cluster;
}
u32 FATFS::end_of_chain_marker() const
{
// Returns the end of chain entry for the given file system.
// Any FAT entry of this value or greater signifies the end
// of the chain has been reached for a given entry.
switch (m_fat_version) {
case FATVersion::FAT12:
return 0xFF8;
case FATVersion::FAT16:
return 0xFFF8;
case FATVersion::FAT32:
return 0x0FFFFFF8;
default:
VERIFY_NOT_REACHED();
}
}
ErrorOr<void> FATFS::set_free_cluster_count(u32 value)
{
VERIFY(m_fat_version == FATVersion::FAT32);
m_fs_info.last_known_free_cluster_count = value;
auto fs_info_buffer = UserOrKernelBuffer::for_kernel_buffer(bit_cast<u8*>(&m_fs_info));
TRY(write_block(m_parameter_block->dos7_bpb()->fs_info_sector, fs_info_buffer, sizeof(m_fs_info)));
return {};
}
ErrorOr<u32> FATFS::allocate_cluster()
{
u32 start_cluster;
if (m_fat_version == FATVersion::FAT32) {
// If we have a hint, start there.
if (m_fs_info.next_free_cluster_hint != fs_info_data_unknown) {
start_cluster = m_fs_info.next_free_cluster_hint;
} else {
// Otherwise, start at the beginning of the data area.
start_cluster = first_data_cluster;
}
} else {
// For FAT12/16, start at the beginning of the data area, as there is no
// FSInfo struct to store the hint.
start_cluster = first_data_cluster;
}
MutexLocker locker(m_lock);
for (u32 i = start_cluster; i < m_parameter_block->sector_count() / m_parameter_block->common_bpb()->sectors_per_cluster; i++) {
if (TRY(fat_read(i)) == 0) {
dbgln_if(FAT_DEBUG, "FATFS: Allocating cluster {}", i);
if (m_fat_version == FATVersion::FAT32 && m_fs_info.last_known_free_cluster_count != fs_info_data_unknown)
TRY(set_free_cluster_count(m_fs_info.last_known_free_cluster_count - 1));
TRY(fat_write(i, end_of_chain_marker()));
return i;
}
}
return Error::from_errno(ENOSPC);
}
ErrorOr<void> FATFS::notify_cluster_freed()
{
if (m_fat_version == FATVersion::FAT32 && m_fs_info.last_known_free_cluster_count != fs_info_data_unknown)
TRY(set_free_cluster_count(m_fs_info.last_known_free_cluster_count + 1));
return {};
}
ErrorOr<u32> FATFS::fat_read(u32 cluster)
{
dbgln_if(FAT_DEBUG, "FATFS: Reading FAT entry for cluster {}", cluster);
u32 fat_offset = fat_offset_for_cluster(cluster);
u32 fat_sector_index = m_parameter_block->common_bpb()->reserved_sector_count + (fat_offset / m_device_block_size);
u32 entry_offset = fat_offset % m_device_block_size;
// NOTE: On FAT12, FATs aren't necessarily block aligned, so in the worst case we have to read
// an extra byte from the next block.
bool read_extra_block = m_fat_version == FATVersion::FAT12 && entry_offset == m_device_block_size - 1;
size_t buffer_size = m_device_block_size;
if (read_extra_block)
buffer_size += m_device_block_size;
auto fat_sector = TRY(KBuffer::try_create_with_size("FATFS: FAT read buffer"sv, buffer_size));
auto fat_sector_buffer = UserOrKernelBuffer::for_kernel_buffer(fat_sector->data());
MutexLocker locker(m_lock);
if (read_extra_block)
TRY(read_blocks(fat_sector_index, 2, fat_sector_buffer));
else
TRY(read_block(fat_sector_index, &fat_sector_buffer, m_device_block_size));
// Look up the next cluster to read, or read End of Chain marker from table.
return cluster_number(*fat_sector, cluster, entry_offset);
}
ErrorOr<void> FATFS::fat_write(u32 cluster, u32 value)
{
dbgln_if(FAT_DEBUG, "FATFS: Writing FAT entry for cluster {} with value {}", cluster, value);
u32 fat_offset = fat_offset_for_cluster(cluster);
u32 fat_sector_index = m_parameter_block->common_bpb()->reserved_sector_count + (fat_offset / m_device_block_size);
u32 entry_offset = fat_offset % m_device_block_size;
// See the comment in fat_read().
bool need_extra_block = m_fat_version == FATVersion::FAT12 && entry_offset == m_device_block_size - 1;
size_t buffer_size = m_device_block_size;
if (need_extra_block)
buffer_size += m_device_block_size;
auto fat_sector = TRY(KBuffer::try_create_with_size("FATFS: FAT read buffer"sv, buffer_size));
auto fat_sector_buffer = UserOrKernelBuffer::for_kernel_buffer(fat_sector->data());
MutexLocker locker(m_lock);
if (need_extra_block)
TRY(read_blocks(fat_sector_index, 2, fat_sector_buffer));
else
TRY(read_block(fat_sector_index, &fat_sector_buffer, m_device_block_size));
switch (m_fat_version) {
case FATVersion::FAT12: {
auto write_misaligned_u16 = [&](u16 word) {
*bit_cast<u8*>(&fat_sector->data()[entry_offset]) = word & 0xFF;
*(bit_cast<u8*>(&fat_sector->data()[entry_offset]) + 1) = word >> 8;
};
u16 existing_bytes_le = 0;
ByteReader::load<u16>(fat_sector->bytes().offset(entry_offset), existing_bytes_le);
u16 existing_bytes = AK::convert_between_host_and_little_endian(existing_bytes_le);
if (cluster % 2 == 0) {
existing_bytes &= 0xF000;
existing_bytes |= static_cast<u16>(value) & 0xFFF;
} else {
existing_bytes &= 0x000F;
existing_bytes |= static_cast<u16>(value) << 4;
}
write_misaligned_u16(AK::convert_between_host_and_little_endian(existing_bytes));
break;
}
case FATVersion::FAT16: {
*bit_cast<u16*>(&fat_sector->data()[entry_offset]) = AK::convert_between_host_and_little_endian(static_cast<u16>(value));
break;
}
case FATVersion::FAT32: {
*bit_cast<u32*>(&fat_sector->data()[entry_offset]) = AK::convert_between_host_and_little_endian(value);
break;
}
}
if (need_extra_block)
TRY(write_blocks(fat_sector_index, 2, fat_sector_buffer));
else
TRY(write_block(fat_sector_index, fat_sector_buffer, m_device_block_size));
return {};
}
u8 FATFS::internal_file_type_to_directory_entry_type(DirectoryEntryView const& entry) const
{
FATAttributes attrib = static_cast<FATAttributes>(entry.file_type);
if (has_flag(attrib, FATAttributes::Directory)) {
return DT_DIR;
} else if (has_flag(attrib, FATAttributes::VolumeID)) {
return DT_UNKNOWN;
} else {
// ReadOnly, Hidden, System, Archive, LongFileName.
return DT_REG;
}
return DT_UNKNOWN;
}
}
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