sendmsg(3p) and recvmsg(3p)

[mkroening]

The kernel should provide system calls corresponding to sendmsg(3p) and recvmsg(3p), which are basic operations of the POSIX socket interface.

These functions are usually used with UDP sockets. They are prominently used in QUIC.

If I understand correctly, we should be able to implement send(3p) on top of sendto(3p) on top of sendmsg(3p) and recv(3p) on top of recvfrom(3p) on top of recvmsg(3p).

For struct msghdr, see <sys/socket.h>.

Our newlib has stubbed these functions for the mean time:

• feat: stub recvmsg and recvmsg newlib#83

IETF RFCs that list these functions as basic operations

• RFC 2292 - Advanced Sockets API for IPv6
• RFC 6458 - Sockets API Extensions for the Stream Control Transmission Protocol (SCTP)
• RFC DRAFT - Sockets API Extensions for In-kernel QUIC Implementations

Respective functions in the Rust ecosystem

• socket2::Socket::sendmsg
• socket2::Socket::recvmsg
• nix::sys::socket::sendmsg
• nix::sys::socket::recvmsg
• tokio_uring::net::UdpSocket::sendmsg
• tokio_uring::net::UdpSocket::recvmsg
• quinn_udp::UdpSocketState::send
• quinn_udp::UdpSocketState::recv