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.
   */
  
  #include <AK/HashTable.h>
  #include <AK/Singleton.h>
  #include <AK/StdLibExtras.h>
  #include <AK/StringView.h>
  #include <Kernel/FileSystem/FIFO.h>
  #include <Kernel/FileSystem/FileDescription.h>
  #include <Kernel/Lock.h>
  #include <Kernel/Process.h>
  #include <Kernel/Thread.h>
  
  //#define FIFO_DEBUG
  
  namespace Kernel {
  
  static AK::Singleton<Lockable<HashTable<FIFO*>>> s_table;
  
  static Lockable<HashTable<FIFO*>>& all_fifos()
  {
      return *s_table;
  }
  
  static int s_next_fifo_id = 1;
  
  NonnullRefPtr<FIFO> FIFO::create(uid_t uid)
  {
      return adopt(*new FIFO(uid));
  }
  
  KResultOr<NonnullRefPtr<FileDescription>> FIFO::open_direction(FIFO::Direction direction)
  {
      auto description = FileDescription::create(*this);
      if (!description.is_error()) {
          attach(direction);
          description.value()->set_fifo_direction({}, direction);
      }
      return description;
  }
  
  KResultOr<NonnullRefPtr<FileDescription>> FIFO::open_direction_blocking(FIFO::Direction direction)
  {
      Locker locker(m_open_lock);
  
      auto description = open_direction(direction);
      if (description.is_error())
          return description;
  
      if (direction == Direction::Reader) {
          m_read_open_queue.wake_all();
  
          if (m_writers == 0) {
              locker.unlock();
              m_write_open_queue.wait_on({}, "FIFO");
              locker.lock();
          }
      }
  
      if (direction == Direction::Writer) {
          m_write_open_queue.wake_all();
  
          if (m_readers == 0) {
              locker.unlock();
              m_read_open_queue.wait_on({}, "FIFO");
              locker.lock();
          }
      }
  
      return description;
  }
  
  FIFO::FIFO(uid_t uid)
      : m_uid(uid)
  {
      LOCKER(all_fifos().lock());
      all_fifos().resource().set(this);
      m_fifo_id = ++s_next_fifo_id;
  
      // Use the same block condition for read and write
      m_buffer.set_unblock_callback([this]() {
          evaluate_block_conditions();
      });
  }
  
  FIFO::~FIFO()
  {
      LOCKER(all_fifos().lock());
      all_fifos().resource().remove(this);
  }
  
  void FIFO::attach(Direction direction)
  {
      if (direction == Direction::Reader) {
          ++m_readers;
  #ifdef FIFO_DEBUG
          klog() << "open reader (" << m_readers << ")";
  #endif
      } else if (direction == Direction::Writer) {
          ++m_writers;
  #ifdef FIFO_DEBUG
          klog() << "open writer (" << m_writers << ")";
  #endif
      }
  
      evaluate_block_conditions();
  }
  
  void FIFO::detach(Direction direction)
  {
      if (direction == Direction::Reader) {
  #ifdef FIFO_DEBUG
          klog() << "close reader (" << m_readers << " - 1)";
  #endif
          ASSERT(m_readers);
          --m_readers;
      } else if (direction == Direction::Writer) {
  #ifdef FIFO_DEBUG
          klog() << "close writer (" << m_writers << " - 1)";
  #endif
          ASSERT(m_writers);
          --m_writers;
      }
  
      evaluate_block_conditions();
  }
  
  bool FIFO::can_read(const FileDescription&, size_t) const
  {
      return !m_buffer.is_empty() || !m_writers;
  }
  
  bool FIFO::can_write(const FileDescription&, size_t) const
  {
      return m_buffer.space_for_writing() || !m_readers;
  }
  
  KResultOr<size_t> FIFO::read(FileDescription&, size_t, UserOrKernelBuffer& buffer, size_t size)
  {
      if (!m_writers && m_buffer.is_empty())
          return 0;
      return m_buffer.read(buffer, size);
  }
  
  KResultOr<size_t> FIFO::write(FileDescription&, size_t, const UserOrKernelBuffer& buffer, size_t size)
  {
      if (!m_readers) {
          Thread::current()->send_signal(SIGPIPE, Process::current());
          return -EPIPE;
      }
      return m_buffer.write(buffer, size);
  }
  
  String FIFO::absolute_path(const FileDescription&) const
  {
      return String::format("fifo:%u", m_fifo_id);
  }
  
  KResult FIFO::stat(::stat& st) const
  {
      memset(&st, 0, sizeof(st));
      st.st_mode = S_IFIFO;
      return KSuccess;
  }
  
  }
  