text: /*
   * Copyright (c) 2018-2020, Andreas Kling <kling@serenityos.org>
   *
   * SPDX-License-Identifier: BSD-2-Clause
   */
  
  #pragma once
  
  #include <AK/Error.h>
  #include <AK/NonnullRefPtr.h>
  #include <AK/RefCounted.h>
  #include <AK/StringView.h>
  #include <AK/Types.h>
  #include <AK/Weakable.h>
  #include <Kernel/Forward.h>
  #include <Kernel/UnixTypes.h>
  #include <Kernel/UserOrKernelBuffer.h>
  #include <Kernel/VirtualAddress.h>
  
  namespace Kernel {
  
  class File;
  
  class FileBlockerSet final : public Thread::BlockerSet {
  public:
      FileBlockerSet() { }
  
      virtual bool should_add_blocker(Thread::Blocker& b, void* data) override
      {
          VERIFY(b.blocker_type() == Thread::Blocker::Type::File);
          auto& blocker = static_cast<Thread::FileBlocker&>(b);
          return !blocker.unblock_if_conditions_are_met(true, data);
      }
  
      void unblock_all_blockers_whose_conditions_are_met()
      {
          SpinlockLocker lock(m_lock);
          BlockerSet::unblock_all_blockers_whose_conditions_are_met_locked([&](auto& b, void* data, bool&) {
              VERIFY(b.blocker_type() == Thread::Blocker::Type::File);
              auto& blocker = static_cast<Thread::FileBlocker&>(b);
              return blocker.unblock_if_conditions_are_met(false, data);
          });
      }
  };
  
  // File is the base class for anything that can be referenced by a OpenFileDescription.
  //
  // 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 Weakable<File> {
  public:
      virtual bool unref() const { return RefCounted<File>::unref(); }
      virtual void will_be_destroyed() { }
      virtual ~File();
  
      virtual ErrorOr<NonnullRefPtr<OpenFileDescription>> open(int options);
      virtual ErrorOr<void> close();
  
      virtual bool can_read(const OpenFileDescription&, u64) const = 0;
      virtual bool can_write(const OpenFileDescription&, u64) const = 0;
  
      virtual ErrorOr<void> attach(OpenFileDescription&);
      virtual void detach(OpenFileDescription&);
      virtual void did_seek(OpenFileDescription&, off_t) { }
      virtual ErrorOr<size_t> read(OpenFileDescription&, u64, UserOrKernelBuffer&, size_t) = 0;
      virtual ErrorOr<size_t> write(OpenFileDescription&, u64, const UserOrKernelBuffer&, size_t) = 0;
      virtual ErrorOr<void> ioctl(OpenFileDescription&, unsigned request, Userspace<void*> arg);
      virtual ErrorOr<Memory::Region*> mmap(Process&, OpenFileDescription&, Memory::VirtualRange const&, u64 offset, int prot, bool shared);
      virtual ErrorOr<struct stat> stat() const { return EBADF; }
  
      // Although this might be better described "name" or "description", these terms already have other meanings.
      virtual ErrorOr<NonnullOwnPtr<KString>> pseudo_path(const OpenFileDescription&) const = 0;
  
      virtual ErrorOr<void> truncate(u64) { return EINVAL; }
      virtual ErrorOr<void> sync() { return EINVAL; }
      virtual ErrorOr<void> chown(OpenFileDescription&, UserID, GroupID) { return EBADF; }
      virtual ErrorOr<void> chmod(OpenFileDescription&, mode_t) { return EBADF; }
  
      virtual StringView class_name() const = 0;
  
      virtual bool is_seekable() const { return false; }
  
      virtual bool is_inode() 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; }
      virtual bool is_inode_watcher() const { return false; }
  
      virtual FileBlockerSet& blocker_set() { return m_blocker_set; }
  
      size_t attach_count() const { return m_attach_count; }
  
  protected:
      File();
  
      void evaluate_block_conditions()
      {
          if (Processor::current_in_irq() != 0) {
              // If called from an IRQ handler we need to delay evaluation
              // and unblocking of waiting threads. Note that this File
              // instance may be deleted until the deferred call is executed!
              Processor::deferred_call_queue([self = make_weak_ptr()]() {
                  if (auto file = self.strong_ref())
                      file->do_evaluate_block_conditions();
              });
          } else {
              do_evaluate_block_conditions();
          }
      }
  
  private:
      ALWAYS_INLINE void do_evaluate_block_conditions()
      {
          VERIFY(!Processor::current_in_irq());
          blocker_set().unblock_all_blockers_whose_conditions_are_met();
      }
  
      FileBlockerSet m_blocker_set;
      size_t m_attach_count { 0 };
  };
  
  }
  