virtio-rng-device

// vi:ft=cpp: -*- Mode: C++ -*-
/*
 * Copyright (C) 2024 Kernkonzept GmbH.
 * Author(s): Martin Kuettler <martin.kuettler@kernkonzept.com>
 *
 * License: see LICENSE.spdx (in this directory or the directories above)
 */
 
#pragma once
 
#include <l4/re/error_helper>
#include <l4/sys/cxx/ipc_epiface>
 
#include <l4/l4virtio/server/virtio>
#include <l4/l4virtio/server/l4virtio>
#include <l4/l4virtio/l4virtio>
 
namespace L4virtio {
namespace Svr {

  template <typename Rnd_state, typename Epiface = L4virtio::Device>
class Virtio_rng : public L4virtio::Svr::Device,
                   public L4::Epiface_t<Virtio_rng<Rnd_state>, Epiface>
{
private:
  enum
    {
      Num_request_queues = 1,
      queue_size = 128,
    };
 
public:
  using Random_state = Rnd_state;

  class Host_irq : public L4::Irqep_t<Host_irq>
  {
  public:
    explicit Host_irq(Virtio_rng *rng) : L4::Irqep_t<Host_irq>(), _rng(rng) {}
 
    void handle_irq()
    {
      _rng->handle_queue();
    }
 
  private:
    Virtio_rng *_rng;
  };

  class Request_processor : public L4virtio::Svr::Request_processor
  {
  public:
    struct Data_buffer : public L4virtio::Svr::Data_buffer
    {
      Data_buffer() = default;
      // This constructor is called from within start, so make it available.
      Data_buffer(L4virtio::Svr::Driver_mem_region const *r,
                  L4virtio::Svr::Virtqueue::Desc const &d,
                  L4virtio::Svr::Request_processor const *)
      {
        pos = static_cast<char *>(r->local(d.addr));
        left = d.len;
      }
    };
 
    Request_processor(L4virtio::Svr::Virtqueue *q, Random_state *rnd,
                      Virtio_rng *rng)
      : _q(q), _rnd(rnd), _rng(rng), _head() {}
 
    bool init_queue()
    {
      auto r = _q->next_avail();
 
      if (L4_UNLIKELY(!r))
        return false;
 
      _head = start(_rng->mem_info(), r, &_req);
 
      return true;
    }
 
    void handle_request()
    {
      if (!_head)
        if (!init_queue())
          return;
 
      for (;;)
        {
          auto const pos = reinterpret_cast<unsigned char *>(_req.pos);
          _rnd->get_random(_req.left, pos);
          _q->finish(_head, _rng, _req.left);
          if (!init_queue())
            break;
        }
      return;
    }
 
  private:
    L4virtio::Svr::Virtqueue *_q;
    Random_state *_rnd;
    Virtio_rng *_rng;
    L4virtio::Svr::Virtqueue::Head_desc _head;
    Data_buffer _req;
  };
 
  Virtio_rng(Random_state *rnd, L4::Registry_iface *registry)
    : L4virtio::Svr::Device(&_dev_config),
      _dev_config(L4VIRTIO_VENDOR_KK, L4VIRTIO_ID_RNG, Num_request_queues),
      _rnd(rnd),
      _host_irq(this),
      _request_processor(&_q, rnd, this)
  {
    init_mem_info(2);
    reset_queue_config(0, queue_size);
    setup_queue(&_q, 0, queue_size);
    registry->register_irq_obj(&_host_irq);
 
    L4virtio::Svr::Dev_config::Features hf;
    hf.ring_indirect_desc() = true;
    _dev_config.host_features(0) = hf.raw;
    _dev_config.set_host_feature(L4VIRTIO_FEATURE_VERSION_1);
    _dev_config.reset_hdr();
  }
 
  void notify_queue(L4virtio::Svr::Virtqueue *)
  {
    if (_q.no_notify_guest())
      return;
 
    _dev_config.add_irq_status(L4VIRTIO_IRQ_STATUS_VRING);
    L4Re::chkipc(_notify_guest_irq->trigger(), "trigger guest irq");
  }
 
  void handle_queue()
  {
    _request_processor.handle_request();
  }
 
  void reset() override
  {
  }
 
  bool check_queues() override
  {
    return true;
  }
 
  int reconfig_queue(unsigned idx) override
  {
    if (idx != 0)
      return -L4_ERANGE;
 
    setup_queue(&_q, 0, queue_size);
 
    return L4_EOK;
  }
 
  void trigger_driver_config_irq() override
  {
    _dev_config.add_irq_status(L4VIRTIO_IRQ_STATUS_CONFIG);
    _notify_guest_irq->trigger();
  }
 
  L4::Ipc_svr::Server_iface *server_iface() const override
  {
    return L4::Epiface::server_iface();
  }
 
  long op_set_status(L4virtio::Device::Rights r, unsigned status)
  {
    return L4virtio::Svr::Device::op_set_status(r, status);
  }
 
  long op_config_queue(L4virtio::Device::Rights r, unsigned queue)
  {
    return L4virtio::Svr::Device::op_config_queue(r, queue);
  }
 
  long op_device_config(L4virtio::Device::Rights r,
                        L4::Ipc::Cap<L4Re::Dataspace> &config_ds,
                        l4_addr_t &ds_offset)
  {
    return L4virtio::Svr::Device::op_device_config(r, config_ds, ds_offset);
  }
 
  L4::Cap<L4::Irq> device_notify_irq() const override
  {
    return L4::cap_cast<L4::Irq>(_host_irq.obj_cap());
  }
 
  void register_single_driver_irq() override
  {
    _notify_guest_irq = L4Re::chkcap
      (server_iface()->template rcv_cap<L4::Irq>(0));
 
    L4Re::chksys(server_iface()->realloc_rcv_cap(0));
  }
 
 
private:
  L4virtio::Svr::Dev_config_t<L4virtio::Svr::No_custom_data>_dev_config;
  Random_state *_rnd;
  L4virtio::Svr::Virtqueue _q;
  Host_irq _host_irq;
  L4::Cap<L4::Irq> _notify_guest_irq;
  Request_processor _request_processor;
};
 
} // namespace Svr
} // namespace L4virtio