text: #pragma once
  
  #include <AK/AKString.h>
  #include <AK/RefCounted.h>
  #include <AK/NonnullRefPtr.h>
  #include <AK/Types.h>
  #include <Kernel/KResult.h>
  #include <Kernel/UnixTypes.h>
  #include <Kernel/VirtualAddress.h>
  
  class FileDescription;
  class Process;
  class Region;
  
  // File is the base class for anything that can be referenced by a FileDescription.
  //
  // The most important functions in File are:
  //
  // read() and write()
  //   - Implement reading and writing.
  //   - Return the number of bytes read/written, OR a negative error code.
  //
  // can_read() and can_write()
  //
  //   - Used to implement blocking I/O, and the select() and poll() syscalls.
  //   - Return true if read() or write() would succeed, respectively.
  //   - Note that can_read() should return true in EOF conditions,
  //     and a subsequent call to read() should return 0.
  //
  // ioctl()
  //
  //   - Optional. If unimplemented, ioctl() on this File will fail with -ENOTTY.
  //   - Can be overridden in subclasses to implement arbitrary functionality.
  //   - Subclasses should take care to validate incoming addresses before dereferencing.
  //
  // mmap()
  //
  //   - Optional. If unimplemented, mmap() on this File will fail with -ENODEV.
  //   - Called by mmap() when userspace wants to memory-map this File somewhere.
  //   - Should create a Region in the Process and return it if successful.
  
  class File : public RefCounted<File> {
  public:
      virtual ~File();
  
      virtual KResultOr<NonnullRefPtr<FileDescription>> open(int options);
      virtual void close();
  
      virtual bool can_read(FileDescription&) const = 0;
      virtual bool can_write(FileDescription&) const = 0;
  
      virtual ssize_t read(FileDescription&, u8*, ssize_t) = 0;
      virtual ssize_t write(FileDescription&, const u8*, ssize_t) = 0;
      virtual int ioctl(FileDescription&, unsigned request, unsigned arg);
      virtual KResultOr<Region*> mmap(Process&, FileDescription&, VirtualAddress preferred_vaddr, size_t offset, size_t size, int prot);
  
      virtual String absolute_path(const FileDescription&) const = 0;
  
      virtual KResult truncate(off_t) { return KResult(-EINVAL); }
  
      virtual const char* class_name() const = 0;
  
      virtual bool is_seekable() const { return false; }
  
      virtual bool is_inode() const { return false; }
      virtual bool is_shared_memory() const { return false; }
      virtual bool is_fifo() const { return false; }
      virtual bool is_device() const { return false; }
      virtual bool is_tty() const { return false; }
      virtual bool is_master_pty() const { return false; }
      virtual bool is_block_device() const { return false; }
      virtual bool is_character_device() const { return false; }
      virtual bool is_socket() const { return false; }
  
  protected:
      File();
  };
  