Side effect of xdp_program__attach with XDP_MODE_HW?

[Daiki AMINAKA]

I faced this and investigating. Just for heads up

I tried code below, once the xdp_program__attach failed with XDP_MODE_HW, other mode also get failed with
libbpf: map 'xsks_map': failed to create: Invalid argument(-22)

If this code start iteration from i == 1, it works with XDP_MODE_SKB after failing with XDP_MODE_NATIVE

    static const struct AttachTypePair {
        enum xdp_attach_mode mode;
        unsigned int xdp_flag;
    } AttachTypePairs[]  = {
        { XDP_MODE_HW, XDP_FLAGS_HW_MODE },
        { XDP_MODE_NATIVE, XDP_FLAGS_DRV_MODE },
        { XDP_MODE_SKB, XDP_FLAGS_SKB_MODE },
    };
    for (uint32_t i = 0; i < ARRAYSIZE(AttachTypePairs); i++) {
        err = xdp_program__attach(prog,  ifIndex, AttachTypePairs[i].mode, 0);
        if (!err) {
            AttachMode = AttachTypePairs[i].mode;
            break;
        }
    }

[Toke Høiland-Jørgensen]

Right, yeah, attaching multiple times with different modes is not really supported, since the attach involves loading the program. So the right thing do to is to restart the operation entirely, reconstructing the xdp_prog structure every time a load is attempted (when mixing modes).

[Daiki AMINAKA]

thanks!