xdp test

env_setup.sh

# vm1 hostip 172.18.18.101(enp0s9), the XDP prog is attached on enp0s9
# vm2 hostip 172.18.18.102(enp0s9)

# exchange id and remoteid vm2
id=1
remoteid=2

ip=172.19.$id.2
ctn=ns1

brctl addbr br1
ip l set br1 up
ip a add 172.19.$id.1/24 dev br1

ip netns add $ctn
ip l add dev vhost type veth peer name vsbx
ip l set dev vsbx netns $ctn
ip netns exec $ctn ip ad add $ip dev vsbx
ip netns exec $ctn ip link set dev vsbx up
ip netns exec $ctn ip route add default via 172.19.$id.1 dev vsbx onlink
ip link set dev vhost up
brctl addif br1 vhost

ip r add 172.19.$remoteid.0/24 via 172.18.18.10$remoteid dev enp0s9

sysctl -w net.ipv4.ip_forward=1
iptables -t filter -P FORWARD ACCEPT

# make sure network setup success before attach XDP prog
ip netns exec ns1 ping 172.19.$remoteid.2

xdp.c

int SEC("xdp/prog1") xdp_dummy(struct xdp_md *ctx) {
    void* data_end = (void*)(long)ctx->data_end;
    void* data = (void*)(long)ctx->data;
    struct ethhdr *eth = data;
    __u32 nh_off = sizeof(*eth);
    if (data+nh_off > data_end){
        return XDP_DROP;
    }
    __be16 eth_proto = eth->h_proto;
    if (eth_proto != BE_ETH_P_IP){
        return XDP_PASS;
    }
  
    struct iphdr *iph = data+nh_off;
    if (iph + 1 > data_end){
        return XDP_DROP;
    }
    __u32 iph_len = iph->ihl<<2;
  
    struct dev *cdev;
    __be32 daddr = iph->daddr;
    cdev = bpf_map_lookup_elem(&local_ips, &daddr);
    if (cdev) {
        memcpy(eth->h_dest, cdev->mac, ETH_ALEN); // mac addr of vsbx
        int res = bpf_redirect_map(&dev_map, cdev->dev_idx, 0); // dev_idx is vhost or br1(both failed)
        if (res == XDP_REDIRECT) {
            bpf_debug("redirect success to %d\n", cdev->dev_idx); // I can see this message in trace_pipe
        } else {
            bpf_debug("redirect failed %d\n", res);
        }
        return res;
    } else {
        bpf_debug("no dev for %x found\n", daddr);
    }
    return XDP_PASS;
}