Hello, Felix Wu, le mar. 18 juil. 2023 18:12:16 -0700, a ecrit: > 02 == SYN so it looks good. But both tcpdump and wireshark (looking into > packet > dump provided by QEMU invocation)
Which packet dump? > I added multiple prints inside slirp and confirmed the ipv6 version of [1] was > reached. > in tcp_output function [2], I got following print: > qemu-system-aarch64: info: Slirp: AF_INET6 out dst ip = > fdb5:481:10ce:0:8c41:aaff:fea9:f674, port = 52190 > qemu-system-aarch64: info: Slirp: AF_INET6 out src ip = fec0::105, port = > 54322 > It looks like there should be something being sent back to the guest, That's what it is. > unless my understanding of tcp_output is wrong. It looks so. > To understand the datapath of guestfwd better, I have the following questions: > 1. What's the meaning of tcp_input and tcp_output? My guess is the following > graph, but I would like to confirm. No, tcp_input is for packets that come from the guest, and tcp_output is for packets that are send to the guest. So it's like that: > tcp_input write_cb host send() > QEMU --------> slirp -----------> QEMU --------------------> host > <-------- <--------- <----------------- > tcp_output slirp_socket_recv host recv() > 2. I don't see port 6655 in the above process. How does slirp know 6655 is the > port that needs to be visited on the host side? Slirp itself *doesn't* know that port. The guestfwd piece just calls the SlirpWriteCb when it has data coming from the guest. See the documentation: /* Set up port forwarding between a port in the guest network and a * callback that will receive the data coming from the port */ SLIRP_EXPORT int slirp_add_guestfwd(Slirp *slirp, SlirpWriteCb write_cb, void *opaque, struct in_addr *guest_addr, int guest_port); and /* This is called by the application for a guestfwd, to provide the data to be * sent on the forwarded port */ SLIRP_EXPORT void slirp_socket_recv(Slirp *slirp, struct in_addr guest_addr, int guest_port, const uint8_t *buf, int size); Samuel