From cb78f4cfaa1ab7bc033ad0e089de9fa84702d1fe Mon Sep 17 00:00:00 2001
From: Eryn Wells <eryn@erynwells.me>
Date: Sun, 24 Apr 2016 19:21:35 -0400
Subject: [PATCH] PageAllocator!

---
 src/SConscript      |   1 +
 src/memory/Pager.cc | 102 ++++++++++++++++++++++++++++++++++++++++++++
 src/memory/Pager.hh |  37 ++++++++++++++++
 3 files changed, 140 insertions(+)
 create mode 100644 src/memory/Pager.cc
 create mode 100644 src/memory/Pager.hh

diff --git a/src/SConscript b/src/SConscript
index b202123..4e6cb2e 100644
--- a/src/SConscript
+++ b/src/SConscript
@@ -26,6 +26,7 @@ files = [
 
     'memory/FrameAllocator.cc',
     'memory/Memory.cc',
+    'memory/Pager.cc',
 ]
 
 toolchain_bin = Dir(os.environ['POLKA_TOOLCHAIN']).Dir('bin')
diff --git a/src/memory/Pager.cc b/src/memory/Pager.cc
new file mode 100644
index 0000000..33b3f09
--- /dev/null
+++ b/src/memory/Pager.cc
@@ -0,0 +1,102 @@
+/* Pager.cc
+ * vim: set tw=80:
+ * Eryn Wells <eryn@erynwells.me>
+ */
+/**
+ * Page tables 'n stuff.
+ */
+
+#include "Attributes.hh"
+#include "Pager.hh"
+#include "kstd/Bitmap.hh"
+#include "memory/Memory.hh"
+
+namespace kernel {
+
+struct PageDirectoryEntry
+{
+    PageDirectoryEntry();
+
+    /** Mark the whole entry not present. */
+    void setNotPresent();
+    bool isNotPresent() const;
+
+    void setAddress(void* address);
+
+private:
+    static const u8 OneBit               = 0;
+    static const u8 ReadWriteBit         = 1;
+    static const u8 UserAccessBit        = 2;
+    static const u8 PageWriteThroughBit  = 3;
+    static const u8 PageCacheDisabledBit = 4;
+    static const u8 AccessedBit          = 5;
+    static const u8 DirtyBit             = 6;
+    static const u8 ZeroBit              = 7;
+    static const u32 IgnoredMask         = 0x00000F00;
+    static const u32 AddressMask         = 0xFFFFF000;
+    static const u32 FlagMask            = 0x00000FFF;
+
+    u32 mEntry;
+
+    void setRequiredBits();
+};
+
+
+PageDirectoryEntry::PageDirectoryEntry()
+    : mEntry(0)
+{
+    static_assert(sizeof(PageDirectoryEntry) == 4, "PageDirectoryEntry must be 4 bytes long.");
+}
+
+
+bool
+PageDirectoryEntry::isNotPresent()
+    const
+{
+    return mEntry == 0;
+}
+
+
+void
+PageDirectoryEntry::setNotPresent()
+{
+    mEntry = 0;
+}
+
+
+void
+PageDirectoryEntry::setAddress(void* address)
+{
+    kstd::Bit::setMask(mEntry, memory::pageAlignDown(uptr(address)), AddressMask);
+}
+
+void
+PageDirectoryEntry::setRequiredBits()
+{
+    kstd::Bit::set(mEntry, OneBit);
+    kstd::Bit::clear(mEntry, ZeroBit);
+    kstd::Bit::clearMask(mEntry, IgnoredMask);
+}
+
+/*
+ * Public
+ */
+
+void
+PageAllocator::initialize(const StartupInformation& startupInformation,
+                          void* pageDirectory)
+{
+    mPageDirectory = reinterpret_cast<PageDirectoryEntry*>(pageDirectory);
+    for (usize i = 0; i < NumberOfEntries; i++) {
+        mPageDirectory[i].setNotPresent();
+    }
+}
+
+/*
+ * Private
+ */
+
+const u16 PageAllocator::NumberOfEntries = 1024;
+
+
+} /* namespace kernel */
diff --git a/src/memory/Pager.hh b/src/memory/Pager.hh
new file mode 100644
index 0000000..3ba6b1b
--- /dev/null
+++ b/src/memory/Pager.hh
@@ -0,0 +1,37 @@
+/* Pager.hh
+ * vim: set tw=80:
+ * Eryn Wells <eryn@erynwells.me>
+ */
+/**
+ * Page tables 'n stuff.
+ */
+
+#ifndef __MEMORY_PAGE_HH__
+#define __MEMORY_PAGE_HH__
+
+#include "StartupInformation.hh"
+#include "kstd/Types.hh"
+
+namespace kernel {
+
+struct PageDirectoryEntry;
+
+/**
+ * Handles allocating pages
+ */
+struct PageAllocator
+{
+    void initialize(const StartupInformation& startupInformation, void* pageDirectory);
+
+    // TODO: A method to install a page table into the system. For per-process page tables, I'll need a way to set the current page table so the system knows where to look.
+
+private:
+    static const u16 NumberOfEntries;
+
+    /** The kernel's page directory. */
+    PageDirectoryEntry* mPageDirectory;
+};
+
+} /* namespace kernel */
+
+#endif /* __MEMORY_PAGE_HH__ */