netdev - Re: [Patch bpf-next v5 1/3] bpf: introduce timeout hash map

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Date:   Thu, 28 Jan 2021 21:57:59 -0800
From:   Cong Wang <xiyou.wangcong@...il.com>
To:     Alexei Starovoitov <alexei.starovoitov@...il.com>
Cc:     Daniel Borkmann <daniel@...earbox.net>,
        Linux Kernel Network Developers <netdev@...r.kernel.org>,
        bpf <bpf@...r.kernel.org>, Jamal Hadi Salim <jhs@...atatu.com>,
        Andrii Nakryiko <andrii@...nel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Martin KaFai Lau <kafai@...com>,
        Cong Wang <cong.wang@...edance.com>,
        Andrii Nakryiko <andrii.nakryiko@...il.com>,
        Dongdong Wang <wangdongdong.6@...edance.com>
Subject: Re: [Patch bpf-next v5 1/3] bpf: introduce timeout hash map

On Thu, Jan 28, 2021 at 6:54 PM Alexei Starovoitov
<alexei.starovoitov@...il.com> wrote:
>
> I meant it would look like:
>
> noinline per_elem_callback(map, key, value, ...)
> {
>   if (value->foo > ...)
>     bpf_delete_map_elem(map, key);
> }
>
> noinline timer_callback(timer, ctx)
> {
>   map = ctx->map;
>   bpf_for_each_map_elem(map, per_elem_callback, ...);
> }
>
> int main_bpf_prog(skb)
> {
>   bpf_timer_setup(my_timer, timer_callback, ...);
>   bpf_mod_timer(my_timer, HZ);
> }
>
> The bpf_for_each_map_elem() work is already in progress. Expect patches to hit
> mailing list soon.

We don't want a per-element timer, we want a per-map timer but that
requires a way to iterate the whole map. If you or other can provide
bpf_for_each_map_elem(), we can certainly build our timeout map
on top of it.

> If you can work on patches for bpf_timer_*() it would be awesome.

Yeah, I will work on this, not only for timeout map, but also possibly for
the ebpf qdisc I plan to add soon.

Thanks.