request_queue.h

/*
 * Copyright (C) 2019-2020 Kernkonzept GmbH.
 * Author(s): Sarah Hoffmann <sarah.hoffmann@kernkonzept.com>
 *
 * This file is distributed under the terms of the GNU General Public
 * License, version 2.  Please see the COPYING-GPL-2 file for details.
 */
#pragma once
 
#include <functional>
#include <deque>
 
#include <l4/cxx/unique_ptr>
 
namespace Block_device {
 
struct Pending_request
{
  struct Owner {};
 
  virtual ~Pending_request() = 0;
 
  virtual int handle_request() = 0;
 
  virtual void fail_request() = 0;
 
  virtual bool is_owner(Owner *owner) = 0;
};
 
inline Pending_request::~Pending_request() = default;
 
struct Request_queue
{
  virtual ~Request_queue() = 0;
 
  virtual void add_to_queue(cxx::unique_ptr<Pending_request> &&request) = 0;
 
  virtual void drain_queue_for(Pending_request::Owner *owner, bool finalize) = 0;
 
  virtual void process_pending() = 0;
 
  virtual bool empty() const = 0;
};
 
inline Request_queue::~Request_queue() = default;
 
class Simple_request_queue : public Request_queue
{
public:
  bool empty() const override { return _queue.empty(); }
 
  void add_to_queue(cxx::unique_ptr<Pending_request> &&request) override
  { _queue.emplace_back(std::move(request)); }
 
  void drain_queue_for(Pending_request::Owner *owner, bool finalize) override
  {
    for (auto it = _queue.begin(); it != _queue.end();)
      {
        if ((*it)->is_owner(owner))
          {
            if (finalize)
              (*it)->fail_request();
            it = _queue.erase(it);
          }
        else
          ++it;
      }
  }
 
  void process_pending() override
  {
    while (!_queue.empty())
      {
        auto &front = _queue.front();
        int ret = front->handle_request();
 
        if (ret == -L4_EBUSY)
          // still no processing unit available, keep element in queue
          return;
 
        if (ret >= 0)
          // request has been sent to hardware
          front.release();
 
        // element was processed, remove it from queue
        _queue.pop_front();
      }
  }
 
private:
  std::deque<cxx::unique_ptr<Pending_request>> _queue;
};
 
} // namespace