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Kernel/FATFS: Implement fat_write

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implicitfield 2024-04-06 15:06:28 +03:00 committed by Tim Schumacher
parent a6a1508601
commit 0f828768bb
Notes: sideshowbarker 2024-07-17 08:43:11 +09:00 
Author: https://github.com/implicitfield
Commit: https://github.com/SerenityOS/serenity/commit/0f828768bb
Pull-request: https://github.com/SerenityOS/serenity/pull/23907
Reviewed-by: https://github.com/Hendiadyoin1
Reviewed-by: https://github.com/cqundefine
Reviewed-by: https://github.com/nico
Reviewed-by: https://github.com/timschumi ✅
2 changed files with 62 additions and 0 deletions
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61
Kernel/FileSystem/FATFS/FileSystem.cpp
View File

@ -365,6 +365,67 @@ ErrorOr<u32> FATFS::fat_read(u32 cluster)
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);

1
Kernel/FileSystem/FATFS/FileSystem.h
View File

@ -88,6 +88,7 @@ private:
u32 cluster_number(KBuffer const& fat_sector, u32 entry_cluster_number, u32 entry_offset) const;
ErrorOr<u32> fat_read(u32 cluster);
ErrorOr<void> fat_write(u32 cluster, u32 value);
OwnPtr<KBuffer> m_boot_record;
OwnPtr<DOSBIOSParameterBlock> m_parameter_block;