AK+Kernel: Implement UUID mixed endianness support

This is being used by GUID partitions so the first three dash-delimited
fields of the GUID are stored in little endian order but the last two
fields are stored in big endian order, hence it's a representation which
is mixed.

3 files changed, 47 insertions, 6 deletions

diff --git a/AK/UUID.cpp b/AK/UUID.cpp
index 4b30f33830..ac76da1464 100644
--- a/AK/UUID.cpp
+++ b/AK/UUID.cpp
@@ -16,7 +16,7 @@ UUID::UUID(Array<u8, 16> uuid_buffer)
     uuid_buffer.span().copy_to(m_uuid_buffer);
 }
 
-void UUID::convert_string_view_to_uuid(StringView uuid_string_view)
+void UUID::convert_string_view_to_little_endian_uuid(StringView uuid_string_view)
 {
     VERIFY(uuid_string_view.length() == 36);
     auto first_unit = MUST(decode_hex(uuid_string_view.substring_view(0, 8)));
@@ -36,9 +36,44 @@ void UUID::convert_string_view_to_uuid(StringView uuid_string_view)
     m_uuid_buffer.span().overwrite(10, fifth_unit.data(), fifth_unit.size());
 }
 
-UUID::UUID(StringView uuid_string_view)
+void UUID::convert_string_view_to_mixed_endian_uuid(StringView uuid_string_view)
 {
-    convert_string_view_to_uuid(uuid_string_view);
+    VERIFY(uuid_string_view.length() == 36);
+    auto first_unit = MUST(decode_hex(uuid_string_view.substring_view(0, 8)));
+    auto second_unit = MUST(decode_hex(uuid_string_view.substring_view(9, 4)));
+    auto third_unit = MUST(decode_hex(uuid_string_view.substring_view(14, 4)));
+    auto fourth_unit = MUST(decode_hex(uuid_string_view.substring_view(19, 4)));
+    auto fifth_unit = MUST(decode_hex(uuid_string_view.substring_view(24, 12)));
+
+    VERIFY(first_unit.size() == 4 && second_unit.size() == 2
+        && third_unit.size() == 2 && fourth_unit.size() == 2
+        && fifth_unit.size() == 6);
+
+    // Revert endianness for first 4 bytes
+    for (size_t index = 0; index < 4; index++) {
+        m_uuid_buffer[3 - index] = first_unit[index];
+    }
+
+    // Revert endianness for second 2 bytes and again for 2 bytes
+    for (size_t index = 0; index < 2; index++) {
+        m_uuid_buffer[3 + 2 - index] = second_unit[index];
+        m_uuid_buffer[5 + 2 - index] = third_unit[index];
+    }
+
+    m_uuid_buffer.span().overwrite(8, fourth_unit.data(), fourth_unit.size());
+    m_uuid_buffer.span().overwrite(10, fifth_unit.data(), fifth_unit.size());
+}
+
+UUID::UUID(StringView uuid_string_view, Endianness endianness)
+{
+    if (endianness == Endianness::Little) {
+        convert_string_view_to_little_endian_uuid(uuid_string_view);
+        return;
+    } else if (endianness == Endianness::Mixed) {
+        convert_string_view_to_mixed_endian_uuid(uuid_string_view);
+        return;
+    }
+    VERIFY_NOT_REACHED();
 }
 
 String UUID::to_string() const
diff --git a/AK/UUID.h b/AK/UUID.h
index 3d69414346..066d301091 100644
--- a/AK/UUID.h
+++ b/AK/UUID.h
@@ -15,9 +15,14 @@ namespace AK {
 
 class UUID {
 public:
+    enum class Endianness {
+        Mixed,
+        Little
+    };
+
     UUID() = default;
     UUID(Array<u8, 16> uuid_buffer);
-    UUID(StringView);
+    UUID(StringView, Endianness endianness = Endianness::Little);
     ~UUID() = default;
 
     bool operator==(const UUID&) const;
@@ -31,7 +36,8 @@ public:
     bool is_zero() const;
 
 private:
-    void convert_string_view_to_uuid(StringView);
+    void convert_string_view_to_little_endian_uuid(StringView);
+    void convert_string_view_to_mixed_endian_uuid(StringView);
 
     Array<u8, 16> m_uuid_buffer {};
 };
diff --git a/Kernel/Storage/StorageManagement.cpp b/Kernel/Storage/StorageManagement.cpp
index 54fe0266bb..cfcdc5b274 100644
--- a/Kernel/Storage/StorageManagement.cpp
+++ b/Kernel/Storage/StorageManagement.cpp
@@ -219,7 +219,7 @@ UNMAP_AFTER_INIT void StorageManagement::determine_boot_device_with_partition_uu
     VERIFY(!m_storage_devices.is_empty());
     VERIFY(m_boot_argument.starts_with(partition_uuid_prefix));
 
-    auto partition_uuid = UUID(m_boot_argument.substring_view(partition_uuid_prefix.length()));
+    auto partition_uuid = UUID(m_boot_argument.substring_view(partition_uuid_prefix.length()), UUID::Endianness::Mixed);
 
     if (partition_uuid.to_string().length() != 36) {
         // FIXME: It would be helpful to output the specified and detected UUIDs in this case,