netdev - Re: [PATCH bpf-next v3 6/8] bpf: Add XDP_REDIRECT support to XDP for bpf_prog

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Date:   Sat, 11 Dec 2021 18:43:56 -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>,
        Andrii Nakryiko <andrii@...nel.org>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...nel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Jesper Dangaard Brouer <hawk@...nel.org>,
        Network Development <netdev@...r.kernel.org>,
        bpf <bpf@...r.kernel.org>
Subject: Re: [PATCH bpf-next v3 6/8] bpf: Add XDP_REDIRECT support to XDP for bpf_prog_run()

On Sat, Dec 11, 2021 at 10:43 AM Toke Høiland-Jørgensen <toke@...hat.com> wrote:
> +
> +static void bpf_test_run_xdp_teardown(struct bpf_test_timer *t)
> +{
> +       struct xdp_mem_info mem = {
> +               .id = t->xdp.pp->xdp_mem_id,
> +               .type = MEM_TYPE_PAGE_POOL,
> +       };

pls add a new line.

> +       xdp_unreg_mem_model(&mem);
> +}
> +
> +static bool ctx_was_changed(struct xdp_page_head *head)
> +{
> +       return (head->orig_ctx.data != head->ctx.data ||
> +               head->orig_ctx.data_meta != head->ctx.data_meta ||
> +               head->orig_ctx.data_end != head->ctx.data_end);

redundant ()

>         bpf_test_timer_enter(&t);
>         old_ctx = bpf_set_run_ctx(&run_ctx.run_ctx);
>         do {
>                 run_ctx.prog_item = &item;
> -               if (xdp)
> +               if (xdp && xdp_redirect) {
> +                       ret = bpf_test_run_xdp_redirect(&t, prog, ctx);
> +                       if (unlikely(ret < 0))
> +                               break;
> +                       *retval = ret;
> +               } else if (xdp) {
>                         *retval = bpf_prog_run_xdp(prog, ctx);

Can we do this unconditionally without introducing a new uapi flag?
I mean "return bpf_redirect()" was a nop under test_run.
What kind of tests might break if it stops being a nop?