[asio-users] A possible patch to enable sendmmsg / recvmmsg (in progress)

[Virgilio F. <vir...@gm...>]

I'm finalizing writing a patch that enables sendmmsg / recvmmsg on
supported operating systems (Linux, [Free/Net/Open]BDS, AIX, Blackberry QNX
Neutrino).

The syscalls are implemented in reactive_socket_service backend only (the
io_uring backend on Linux does not support sendmmsg / recvmmsg yet).

The config.hpp has macros for forcible disable those calls, and detect
supported operating system compiler macros.

New methods were developed for (send/send_to/receive/receive_from) suffixed
with '_multiple_buffer_sequence' that accepts a multiple_buffer_sequence
class (backed by asio::detail::array<multiple_buffer_sequence_op, N> or
std::vector<multiple_buffer_sequence_op>) and a
multiple_buffer_sequence_adapter that convert ops to struct mmsghdr* for
sendmmsg/recvmmsg.

The multiple_buffer_sequence implementations are basically a collection
of multiple_buffer_sequence_op instances that represents each socket
operation .

<code>
  buffer_sequence_type buffer_sequence_;
  buffer_sequence_adapter_type buffer_sequence_adapter_;
  endpoint_type endpoint_;
  bool completed_;
  socket_base::message_flags flags_;
  std::size_t bytes_transferred_;
  asio::error_code error_code_;
</code>

The multiple_buffer_sequence implementations has full container support,
iterators, and support Mutable and Const buffer sequences.

The patch is near a first working version (need to finalize work on
handlers yet), but I made the code available for review, scrutiny and
suggestions.

The source code is in my github repo (
https://github.com/virgiliofornazin/asio),
on branch feature/multiple_datagram_buffers_sequence-io-sendmmsg-recvmmsg

( full URL:
https://github.com/chriskohlhoff/asio/compare/master...virgiliofornazin:asio:feature/multiple_datagram_buffers_sequence-io-sendmmsg-recvmmsg
)