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

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Date:   Sun, 31 Jan 2021 15:35:17 -0500
From:   Jamal Hadi Salim <jhs@...atatu.com>
To:     Alexei Starovoitov <alexei.starovoitov@...il.com>
Cc:     Cong Wang <xiyou.wangcong@...il.com>,
        Daniel Borkmann <daniel@...earbox.net>,
        Linux Kernel Network Developers <netdev@...r.kernel.org>,
        bpf <bpf@...r.kernel.org>, 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 2021-01-29 10:14 p.m., Alexei Starovoitov wrote:
> On Fri, Jan 29, 2021 at 6:14 AM Jamal Hadi Salim <jhs@...atatu.com> wrote:
>>
>> On 2021-01-29 9:06 a.m., Jamal Hadi Salim wrote:
>>
>>> Which leads to:
>>> Why not extend the general feature so one can register for optional
>>> callbacks not just for expire but also add/del/update on specific
>>> entries or table?
>>> add/del/update could be sourced from other kernel programs or user space
>>> and the callback would be invoked before an entry is added/deleted etc.
>>> (just like it is here for expiry).
>>
>> Sorry - shouldve read the rest of the thread:
>> Agree with Cong that you want per-map but there are use cases where you
>> want it per entry (eg the add/del/update case).
> 
> That was my point as well.
> bpf_timer api should be generic, so that users can do both.
> The program could use bpf_timer one for each flow and bpf_timer for each map.
> And timers without maps.

I like it. Sensible to also have callback invocations for map
changes i.e entry create/update/delete (maybe map create/destroy).

cheers,
jamal