text: /*
   * Copyright (c) 2018-2020, Andreas Kling <kling@serenityos.org>
   * All rights reserved.
   *
   * Redistribution and use in source and binary forms, with or without
   * modification, are permitted provided that the following conditions are met:
   *
   * 1. Redistributions of source code must retain the above copyright notice, this
   *    list of conditions and the following disclaimer.
   *
   * 2. Redistributions in binary form must reproduce the above copyright notice,
   *    this list of conditions and the following disclaimer in the documentation
   *    and/or other materials provided with the distribution.
   *
   * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
   * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
   * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
   * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
   * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
   * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
   * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
   * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
   * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
   * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
   */
  
  #pragma once
  
  #include <AK/NonnullRefPtr.h>
  #include <Kernel/Assertions.h>
  #include <Kernel/Heap/SlabAllocator.h>
  #include <Kernel/VM/PhysicalAddress.h>
  
  class PhysicalPage {
      friend class MemoryManager;
      friend class PageDirectory;
      friend class VMObject;
  
      MAKE_SLAB_ALLOCATED(PhysicalPage)
  public:
      PhysicalAddress paddr() const { return m_paddr; }
  
      void ref()
      {
          ASSERT(m_retain_count);
          ++m_retain_count;
      }
  
      void deref()
      {
          ASSERT(m_retain_count);
          if (!--m_retain_count) {
              if (m_may_return_to_freelist)
                  move(*this).return_to_freelist();
              delete this;
          }
      }
  
      static NonnullRefPtr<PhysicalPage> create(PhysicalAddress, bool supervisor, bool may_return_to_freelist = true);
  
      u16 ref_count() const { return m_retain_count; }
  
  private:
      PhysicalPage(PhysicalAddress paddr, bool supervisor, bool may_return_to_freelist = true);
      ~PhysicalPage() {}
  
      void return_to_freelist() &&;
  
      u16 m_retain_count { 1 };
      bool m_may_return_to_freelist { true };
      bool m_supervisor { false };
      PhysicalAddress m_paddr;
  };
  