From f9f047f519d0100c40b914d3ce777ac2f8430b38 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Matteo=20Gm=C3=BCr?= <matteo.gmuer1@ost.ch>
Date: Mon, 28 Oct 2024 15:18:31 +0000
Subject: Add is empty check method for page table

---
 arch/x86_64/src/memory/paging/page_table.cpp | 55 ++++++++++++----------------
 1 file changed, 23 insertions(+), 32 deletions(-)

(limited to 'arch/x86_64/src/memory/paging')

diff --git a/arch/x86_64/src/memory/paging/page_table.cpp b/arch/x86_64/src/memory/paging/page_table.cpp
index a01c431..64a4fd9 100644
--- a/arch/x86_64/src/memory/paging/page_table.cpp
+++ b/arch/x86_64/src/memory/paging/page_table.cpp
@@ -1,5 +1,6 @@
 #include "arch/memory/paging/page_table.hpp"
 
+#include <algorithm>
 #include <array>
 #include <memory>
 
@@ -16,31 +17,16 @@ namespace teachos::arch::memory::paging
    */
   struct page_table
   {
-    /**
-     * @brief Set every entry of the page to unused.
-     */
     auto zero_entries() -> void;
 
-    /**
-     * @brief Returns the next page table level from the given page table index. Meaning we use an index into a Level 4
-     * page table to get the according Level 3 page table.
-     *
-     * @note This method
-     * should not be called on a Level 1 page table, because there is no furthere page table and mangeling up and
-     * returning the physical address would cause hard to debug issues.
-     *
-     * @param table_index Index of this page table in the page table one level lower.
-     */
-    auto next_table(std::size_t table_index) -> std::optional<page_table *>;
+    auto is_empty() const -> bool;
+
+    auto next_table(std::size_t table_index) const -> std::optional<page_table *>;
 
-    /**
-     * @brief Index operator overload to access specific entries directy.
-     *
-     * @param index Index of the entry we want to access and read or write too.
-     * @return Entry at the given table index.
-     */
     auto operator[](std::size_t index) -> entry &;
 
+    auto operator[](std::size_t index) const -> entry const &;
+
   private:
     /**
      * @brief Calculates the address of the next page table level for the given table index.
@@ -51,7 +37,7 @@ namespace teachos::arch::memory::paging
      * @param table_index Index of this page table in the page table one level higher.
      * @return An optional of the address of the next page table or null.
      */
-    auto next_table_address(std::size_t table_index) -> std::optional<std::size_t>;
+    auto next_table_address(std::size_t table_index) const -> std::optional<std::size_t>;
 
     std::array<entry, PAGE_TABLE_ENTRY_COUNT> entries =
         {};  ///< Entries containing addresses to page tables of a level below or
@@ -60,16 +46,15 @@ namespace teachos::arch::memory::paging
 
   auto page_table::zero_entries() -> void
   {
-    std::size_t constexpr entry_amount = sizeof(entries) / sizeof(entries[0]);
-    static_assert(entry_amount == PAGE_TABLE_ENTRY_COUNT);
-    for (std::size_t i = 0; i < entry_amount; ++i)
-    {
-      auto entry = this->operator[](i);
-      entry.set_unused();
-    }
+    std::ranges::for_each(entries, [](entry & entry) { entry.set_unused(); });
+  }
+
+  auto page_table::is_empty() const -> bool
+  {
+    return std::all_of(entries.begin(), entries.end(), [](entry const & entry) { return entry.is_unused(); });
   }
 
-  auto page_table::next_table(std::size_t table_index) -> std::optional<page_table *>
+  auto page_table::next_table(std::size_t table_index) const -> std::optional<page_table *>
   {
     auto const address = next_table_address(table_index);
     if (address.has_value())
@@ -81,13 +66,17 @@ namespace teachos::arch::memory::paging
 
   auto page_table::operator[](std::size_t index) -> entry &
   {
-    // C array is not bounds checked, therefore we have to check ourselves, to ensure no out of bounds reads, which
-    // could be incredibly hard to debug later.
     exception_handling::assert(index < PAGE_TABLE_ENTRY_COUNT, "[Page Table] Index out of bounds");
     return entries[index];
   }
 
-  auto page_table::next_table_address(std::size_t table_index) -> std::optional<std::size_t>
+  auto page_table::operator[](std::size_t index) const -> entry const &
+  {
+    exception_handling::assert(index < PAGE_TABLE_ENTRY_COUNT, "[Page Table] Index out of bounds");
+    return entries[index];
+  }
+
+  auto page_table::next_table_address(std::size_t table_index) const -> std::optional<std::size_t>
   {
     auto const entry = this->operator[](table_index);
 
@@ -130,6 +119,8 @@ namespace teachos::arch::memory::paging
 
   auto page_table_handle::zero_entries() -> void { handle->zero_entries(); }
 
+  auto page_table_handle::is_empty() const -> bool { return handle->is_empty(); }
+
   auto page_table_handle::next_table(std::size_t table_index) -> std::optional<page_table_handle>
   {
     exception_handling::assert(handle_level != page_table_handle::LEVEL1,
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