Bitmap: Add a 'find_and_toggle' method

Just like find(), but toggles the value when finding it.
Avoids doing this manually in MemoryManager and KernelVM.

kernel/src/memory/KernelVM.cpp

@@ -30,12 +30,11 @@ namespace KernelVM
     {
         auto kernelvm_bitmap = g_kernelvm_bitmap.lock();
 
-        const auto maybe_index = kernelvm_bitmap->find(false);
+        const auto maybe_index = kernelvm_bitmap->find_and_toggle(false);
         if (!maybe_index.has_value()) return err(ENOMEM);
 
         const usize index = maybe_index.value();
 
-        kernelvm_bitmap->set(index, true);
         g_used_vm += ARCH_PAGE_SIZE;
 
         return KERNEL_VM_RANGE_START + (index * ARCH_PAGE_SIZE);

kernel/src/memory/MemoryManager.cpp

@@ -146,13 +146,15 @@ namespace MemoryManager
     {
         auto frame_bitmap = g_frame_bitmap.lock();
 
-        const auto maybe_index = frame_bitmap->find(false, start_index);
+        const auto maybe_index = frame_bitmap->find_and_toggle(false, start_index);
         if (!maybe_index.has_value()) return err(ENOMEM);
 
         const usize index = maybe_index.value();
 
         start_index = index + 1;
-        do_lock_frame(index, *frame_bitmap);
+
+        used_mem += ARCH_PAGE_SIZE;
+        free_mem -= ARCH_PAGE_SIZE;
 
         return index * ARCH_PAGE_SIZE;
     }

luna/include/luna/Bitmap.h

@@ -1,5 +1,5 @@
 #pragma once
-#include <luna/Option.h>
+#include <luna/Result.h>
 #include <luna/Types.h>
 
 class Bitmap
@@ -37,6 +37,8 @@ class Bitmap
 
     Option<usize> find(bool value, usize begin = 0) const;
 
+    Option<usize> find_and_toggle(bool value, usize begin = 0);
+
     void clear(bool value);
     void clear_region(usize start, usize bits, bool value);
 

luna/src/Bitmap.cpp

@@ -125,3 +125,10 @@ Option<usize> Bitmap::find(bool value, usize begin) const
 
     return {};
 }
+
+Option<usize> Bitmap::find_and_toggle(bool value, usize begin)
+{
+    usize index = TRY(find(value, begin));
+    set(index, !value);
+    return index;
+}