SO_INQ makes recvmsg() return the bytes left in the receive queue in an SCM_INQ cmsg, saving a SIOCINQ call per receive. AF_UNIX stream sockets support it, AF_VSOCK fails with ENOPROTOOPT. Add it for SOCK_STREAM, reusing the hint already computed for io_uring. As with TCP_INQ, 1 is reported once the stream is finished so the caller reads again and sees EOF, and accepted sockets inherit the setting from the listener. No cmsg is sent when the transport cannot report the queue length. SOCK_SEQPACKET is refused, as on AF_UNIX: its transport callback counts messages, not bytes. Signed-off-by: David Carlier <devnexen@gmail.com> Reviewed-by: Stefano Garzarella <sgarzare@redhat.com> Link: https://patch.msgid.link/20261016132716.272018-3-devnexen@gmail.com Signed-off-by: Paolo Abeni <pabeni@redhat.com>