netdev - Re: [PATCH bpf-next v5 7/7] selftests/bpf: Add selftest for XDP_REDIRECT in bpf_prog

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Date:   Wed, 5 Jan 2022 20:20:27 -0800
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     Toke Høiland-Jørgensen <toke@...hat.com>
Cc:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Jesper Dangaard Brouer <hawk@...nel.org>,
        John Fastabend <john.fastabend@...il.com>,
        Andrii Nakryiko <andrii@...nel.org>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        KP Singh <kpsingh@...nel.org>, Shuah Khan <shuah@...nel.org>,
        netdev@...r.kernel.org, bpf@...r.kernel.org
Subject: Re: [PATCH bpf-next v5 7/7] selftests/bpf: Add selftest for
 XDP_REDIRECT in bpf_prog_run()

On Mon, Jan 03, 2022 at 04:08:12PM +0100, Toke Høiland-Jørgensen wrote:
> +
> +#define NUM_PKTS 3

May be send a bit more than 3 packets?
Just to test skb_list logic for XDP_PASS.

> +
> +	/* We setup a veth pair that we can not only XDP_REDIRECT packets
> +	 * between, but also route them. The test packet (defined above) has
> +	 * address information so it will be routed back out the same interface
> +	 * after it has been received, which will allow it to be picked up by
> +	 * the XDP program on the destination interface.
> +	 *
> +	 * The XDP program we run with bpf_prog_run() will cycle through all
> +	 * four return codes (DROP/PASS/TX/REDIRECT), so we should end up with
> +	 * NUM_PKTS - 1 packets seen on the dst iface. We match the packets on
> +	 * the UDP payload.
> +	 */
> +	SYS("ip link add veth_src type veth peer name veth_dst");
> +	SYS("ip link set dev veth_src address 00:11:22:33:44:55");
> +	SYS("ip link set dev veth_dst address 66:77:88:99:aa:bb");
> +	SYS("ip link set dev veth_src up");
> +	SYS("ip link set dev veth_dst up");
> +	SYS("ip addr add dev veth_src fc00::1/64");
> +	SYS("ip addr add dev veth_dst fc00::2/64");
> +	SYS("ip neigh add fc00::2 dev veth_src lladdr 66:77:88:99:aa:bb");
> +	SYS("sysctl -w net.ipv6.conf.all.forwarding=1");

These commands pollute current netns. The test has to create its own netns
like other tests do.

The forwarding=1 is odd. Nothing in the comments or commit logs
talks about it.
I'm guessing it's due to patch 6 limitation of picking loopback
for XDP_PASS and XDP_TX, right?
There is ingress_ifindex field in struct xdp_md.
May be use that to setup dev and rxq in test_run in patch 6?
Then there will be no need to hack through forwarding=1 ?