ipc_basics

// vi:set ft=cpp: -*- Mode: C++ -*-
/*
 * (c) 2014 Alexander Warg <alexander.warg@kernkonzept.com>
 *
 * License: see LICENSE.spdx (in this directory or the directories above)
 */
#pragma once
 
#include "types"
#include <l4/sys/utcb.h>
#include <l4/sys/err.h>
 
namespace L4 {

namespace Ipc {

namespace Msg {

constexpr unsigned long align_to(unsigned long bytes, unsigned long align) noexcept
{ return (bytes + align - 1) & ~(align - 1); }

template<typename T>
constexpr unsigned long align_to(unsigned long bytes) noexcept
{ return align_to(bytes, __alignof(T)); }

template<typename T>
constexpr bool check_size(unsigned offset, unsigned limit) noexcept
{
  return offset + sizeof(T) <= limit;
}

template<typename T, typename CTYPE>
inline bool check_size(unsigned offset, unsigned limit, CTYPE cnt) noexcept
{
  if (L4_UNLIKELY(sizeof(CTYPE) <= sizeof(unsigned) &&
                  ~0U / sizeof(T) <= static_cast<unsigned>(cnt)))
    return false;
 
  if (L4_UNLIKELY(sizeof(CTYPE) > sizeof(unsigned) &&
                  static_cast<CTYPE>(~0U / sizeof(T)) <= cnt))
    return false;
 
  return sizeof(T) * cnt <= limit - offset;
}
 
 
enum
{
  Word_bytes = sizeof(l4_umword_t),
  Item_words = 2,
  Item_bytes = Word_bytes * Item_words,
  Mr_words   = L4_UTCB_GENERIC_DATA_SIZE,
  Mr_bytes   = Word_bytes * Mr_words,
  Br_bytes   = Word_bytes * L4_UTCB_GENERIC_BUFFERS_SIZE,
};
 

template<typename T>
inline int msg_add(char *msg, unsigned offs, unsigned limit, T v) noexcept
{
  offs = align_to<T>(offs);
  if (L4_UNLIKELY(!check_size<T>(offs, limit)))
    return -L4_EMSGTOOLONG;
  *reinterpret_cast<L4::Types::Remove_const_t<T> *>(msg + offs) = v;
  return offs + sizeof(T);
}

template<typename T>
inline int msg_get(char *msg, unsigned offs, unsigned limit, T &v) noexcept
{
  offs = align_to<T>(offs);
  if (L4_UNLIKELY(!check_size<T>(offs, limit)))
    return -L4_EMSGTOOSHORT;
  v = *reinterpret_cast<T *>(msg + offs);
  return offs + sizeof(T);
}

enum class Phase
{
  Data,     
  Items,    
  Buffers,  
};
 
// implementation details
namespace Detail {
 
// Helper struct to get the plain type of the IPC argument. The various
// specializations remove the pointer or reference.
template<typename T> struct _Plain
{
  using type = T;
  static T &deref(T &v) noexcept { return v; }
  static T const &deref(T const &v) noexcept { return v; }
};
 
template<typename T> struct _Plain<T *>
{
  using type = T;
  static T &deref(T *v) noexcept { return *v; }
};
 
template<typename T> struct _Plain<T &>
{
  using type = T;
  static T &deref(T &v) noexcept { return v; }
 
};
 
template<typename T> struct _Plain<T const &>
{
  using type = T;
  static T const &deref(T const &v) noexcept { return v; }
};
 
template<typename T> struct _Plain<T const *>
{
  using type = T;
  static T const &deref(T const *v) noexcept { return *v; }
};
 
}

template<typename T> struct Clnt_noops
{
  static constexpr int to_msg_data([[maybe_unused]] char *msg, unsigned offset,
                                   [[maybe_unused]] unsigned limit,
                                   [[maybe_unused]] T const &arg) noexcept
  { return offset; }

  static constexpr int to_msg_items([[maybe_unused]] char *msg, unsigned offset,
                                    [[maybe_unused]] unsigned limit,
                                    [[maybe_unused]] T const &arg) noexcept
  { return offset; }

  static constexpr int to_msg_buffers([[maybe_unused]] char *brs,
                                      unsigned offset,
                                      [[maybe_unused]] unsigned limit,
                                      [[maybe_unused]] T const &arg) noexcept
  { return offset; }

  static constexpr int from_msg_data([[maybe_unused]] char *msg,
                                     unsigned offset,
                                     [[maybe_unused]] unsigned limit,
                                     [[maybe_unused]] T &arg) noexcept
  { return offset; }

  static constexpr int from_msg_items([[maybe_unused]] char *msg,
                                      unsigned offset,
                                      [[maybe_unused]] unsigned limit,
                                      [[maybe_unused]] T &arg) noexcept
  { return offset; }
};

template<typename T> struct Svr_noops
{
  static constexpr int from_svr_data([[maybe_unused]] char *msg,
                                     unsigned offset,
                                     [[maybe_unused]] unsigned limit,
                                     [[maybe_unused]] T const &arg) noexcept
  { return offset; }

  static constexpr int from_svr_items([[maybe_unused]] char *msg,
                                      unsigned offset,
                                      [[maybe_unused]] unsigned limit,
                                      [[maybe_unused]] T const &arg) noexcept
  { return offset; }

  static constexpr int reserve_data([[maybe_unused]] char *msg,
                                    unsigned offset,
                                    [[maybe_unused]] unsigned limit,
                                    [[maybe_unused]] T &arg) noexcept
  { return offset; }

  static constexpr int to_svr_data([[maybe_unused]] char *msg,
                                   unsigned offset,
                                   [[maybe_unused]] unsigned limit,
                                   [[maybe_unused]] T &arg) noexcept
  { return offset; }

  static constexpr int to_svr_items([[maybe_unused]] char *msg,
                                    unsigned offset,
                                    [[maybe_unused]] unsigned limit,
                                    [[maybe_unused]] T &arg) noexcept
  { return offset; }
};

template<typename MTYPE>
struct Clnt_val_ops : Clnt_noops<MTYPE>
{
  static_assert(L4::Types::Is_trivially_copyable_v<MTYPE>,
                "Only trivially copyable types can be used as IPC arguments");

  static int to_msg_data(char *msg, unsigned offset, unsigned limit,
                         MTYPE const &arg) noexcept
  { return msg_add<MTYPE>(msg, offset, limit, arg); }

  static int from_msg_data(char *msg, unsigned offset, unsigned limit,
                           MTYPE &arg) noexcept
  { return msg_get<MTYPE>(msg, offset, limit, arg); }
};

template<typename MTYPE>
struct Svr_val_ops : Svr_noops<MTYPE>
{
  static_assert(L4::Types::Is_trivially_copyable_v<MTYPE>,
                "Only trivially copyable types can be used as IPC arguments");

  static int to_svr_data(char *msg, unsigned offset, unsigned limit,
                         MTYPE &arg) noexcept
  { return msg_get<MTYPE>(msg, offset, limit, arg); }

  static int reserve_data(char *, unsigned offs, unsigned limit,
                          MTYPE &) noexcept
  {
    offs = align_to<MTYPE>(offs);
    if (L4_UNLIKELY(!check_size<MTYPE>(offs, limit)))
      return -L4_EMSGTOOLONG;
    return offs + sizeof(MTYPE);
  }

  static int from_svr_data(char *msg, unsigned offset, unsigned limit,
                           MTYPE const &arg) noexcept
  { return msg_add<MTYPE>(msg, offset, limit, arg); }
};

template<typename T> struct Elem
{
  using arg_type = T;
  using svr_type = T;
  using svr_arg_type = T; // might be const & (depending on the size)
  static constexpr bool Is_optional = false;
  static constexpr bool Is_input = true;
  static constexpr bool Is_output = false;
};
 
template<typename T> struct Elem<T &>
{
  using arg_type = T &;
  using svr_type = T;
  using svr_arg_type = T &;
  static constexpr bool Is_optional = false;
  static constexpr bool Is_input = false;
  static constexpr bool Is_output = true;
};
 
template<typename T> struct Elem<T const &>
{
  using arg_type = T const &;
  using svr_type = T;
  // as the RPC uses a const reference we use it here too,
  // we could also use pass by value depending on the size
  using svr_arg_type = T const &;
  static constexpr bool Is_optional = false;
  static constexpr bool Is_input = true;
  static constexpr bool Is_output = false;
};
 
template<typename T> struct Elem<T *> : Elem<T &>
{
  using arg_type = T *;
};
 
template<typename T> struct Elem<T const *> : Elem<T const &>
{
  using arg_type = T const *;
};

template<typename T> struct Is_valid_rpc_type : L4::Types::True {};
 
template<typename T>
struct _Elem : Elem<T>
{
  static_assert(Is_valid_rpc_type<T>::value,
                "L4::Ipc::Msg::_Elem<T>: type T is not a valid RPC parameter type.");
};
 
namespace Detail {
 
template<typename T>
struct _Clnt_val_ops :
  Clnt_val_ops<typename Detail::_Plain<T>::type> {};
 
template<typename T,
         typename ELEM = _Elem<T>,
         typename CLNT_OPS = _Clnt_val_ops<typename ELEM::arg_type>
         >
struct _Clnt_xmit : CLNT_OPS {};
 
template<typename T,
         typename ELEM = _Elem<T>,
         typename SVR_OPS = Svr_val_ops<typename ELEM::svr_type>
         >
struct _Svr_xmit : SVR_OPS {};
 
} //namespace Detail
 
// Specialize to alias a type X to T in client call signature.
// Needs to be combined with a matching Elem< X > : Elem< T > specialization.
// Or alternatively X needs to inherit from T.
template<typename T> struct Clnt_xmit : Detail::_Clnt_xmit<T> {};
// Specialize to alias a type X to T in server op_... signature.
// Needs to be combined with a matching Elem< X > : Elem< T > specialization.
// Or alternatively X needs to inherit from T.
template<typename T> struct Svr_xmit : Detail::_Svr_xmit<T> {};
 
}}} // namespace Msg, Ipc, L4