serenity/Kernel/Storage/Partition/GUIDPartitionTable.cpp

/*
 * Copyright (c) 2020, Liav A. <liavalb@hotmail.co.il>
 *
 * SPDX-License-Identifier: BSD-2-Clause
 */

#include <AK/AllOf.h>
#include <AK/Array.h>
#include <Kernel/Debug.h>
#include <Kernel/Storage/Partition/GUIDPartitionTable.h>

namespace Kernel {

#define GPT_SIGNATURE2 0x54524150
#define GPT_SIGNATURE 0x20494645
#define BytesPerSector 512

struct [[gnu::packed]] GPTPartitionEntry {
    u8 partition_guid[16];
    u8 unique_guid[16];

    u64 first_lba;
    u64 last_lba;

    u64 attributes;
    char partition_name[72];
};

struct [[gnu::packed]] GUIDPartitionHeader {
    u32 sig[2];
    u32 revision;
    u32 header_size;
    u32 crc32_header;
    u32 reserved;
    u64 current_lba;
    u64 backup_lba;

    u64 first_usable_lba;
    u64 last_usable_lba;

    u64 disk_guid1[2];

    u64 partition_array_start_lba;

    u32 entries_count;
    u32 partition_entry_size;
    u32 crc32_entries_array;
};

Result<NonnullOwnPtr<GUIDPartitionTable>, PartitionTable::Error> GUIDPartitionTable::try_to_initialize(const StorageDevice& device)
{
    auto table = make<GUIDPartitionTable>(device);
    if (!table->is_valid())
        return { PartitionTable::Error::Invalid };
    return table;
}

GUIDPartitionTable::GUIDPartitionTable(const StorageDevice& device)
    : MBRPartitionTable(device)
{
    // FIXME: Handle OOM failure here.
    m_cached_header = ByteBuffer::create_zeroed(m_device->block_size()).release_value();
    VERIFY(partitions_count() == 0);
    if (!initialize())
        m_valid = false;
}

const GUIDPartitionHeader& GUIDPartitionTable::header() const
{
    return *(const GUIDPartitionHeader*)m_cached_header.data();
}

bool GUIDPartitionTable::initialize()
{
    VERIFY(m_cached_header.data() != nullptr);

    auto first_gpt_block = (m_device->block_size() == 512) ? 1 : 0;

    auto buffer = UserOrKernelBuffer::for_kernel_buffer(m_cached_header.data());
    if (!m_device->read_block(first_gpt_block, buffer)) {
        return false;
    }

    dbgln_if(GPT_DEBUG, "GUIDPartitionTable: signature - {:#08x} {:#08x}", header().sig[1], header().sig[0]);

    if (header().sig[0] != GPT_SIGNATURE && header().sig[1] != GPT_SIGNATURE2) {
        dbgln("GUIDPartitionTable: bad signature {:#08x} {:#08x}", header().sig[1], header().sig[0]);
        return false;
    }

    auto entries_buffer_result = ByteBuffer::create_zeroed(m_device->block_size());
    if (!entries_buffer_result.has_value()) {
        dbgln("GUIPartitionTable: not enough memory for entries buffer");
        return false;
    }
    auto entries_buffer = entries_buffer_result.release_value();
    auto raw_entries_buffer = UserOrKernelBuffer::for_kernel_buffer(entries_buffer.data());
    size_t raw_byte_index = header().partition_array_start_lba * m_device->block_size();
    for (size_t entry_index = 0; entry_index < header().entries_count; entry_index++) {

        if (!m_device->read_block((raw_byte_index / m_device->block_size()), raw_entries_buffer)) {
            return false;
        }
        auto* entries = (const GPTPartitionEntry*)entries_buffer.data();
        auto& entry = entries[entry_index % (m_device->block_size() / (size_t)header().partition_entry_size)];
        Array<u8, 16> partition_type {};
        partition_type.span().overwrite(0, entry.partition_guid, partition_type.size());

        if (is_unused_entry(partition_type)) {
            raw_byte_index += header().partition_entry_size;
            continue;
        }

        Array<u8, 16> unique_guid {};
        unique_guid.span().overwrite(0, entry.unique_guid, unique_guid.size());
        dbgln("Detected GPT partition (entry={}), offset={}, limit={}", entry_index, entry.first_lba, entry.last_lba);
        m_partitions.append({ entry.first_lba, entry.last_lba, partition_type, unique_guid, entry.attributes });
        raw_byte_index += header().partition_entry_size;
    }

    return true;
}

bool GUIDPartitionTable::is_unused_entry(Array<u8, 16> partition_type) const
{
    return all_of(partition_type, [](const auto octet) { return octet == 0; });
}

}