netdev - Re: [RFC PATCH v3 0/3] Introduce BPF map tracing capability

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Message-ID: <1376ab2d-f412-f001-a173-75af12f4ce98@mojatatu.com>
Date:   Thu, 4 Nov 2021 07:08:49 -0400
From:   Jamal Hadi Salim <jhs@...atatu.com>
To:     Joe Burton <jevburton.kernel@...il.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>, linux-kernel@...r.kernel.org,
        netdev@...r.kernel.org, bpf@...r.kernel.org,
        Petar Penkov <ppenkov@...gle.com>,
        Stanislav Fomichev <sdf@...gle.com>,
        Joe Burton <jevburton@...gle.com>
Subject: Re: [RFC PATCH v3 0/3] Introduce BPF map tracing capability

On 2021-11-04 06:59, Jamal Hadi Salim wrote:
> On 2021-11-03 13:12, Joe Burton wrote:
>> That's a good point. Since the probe is invoked before the update takes
>> place, it would not be possible to account for the possibility that the
>> update failed.
>>
>> Unless someone wants the `pre update' hook, I'll simply adjust the
>> existing hooks' semantics so that they are invoked after the update.
>> As discussed, this better suits the intended use case.
>>
> 
> If the goal is to synchronize state between two maps (if i understood
> correctly the intent) then it is more useful to go post-update.
> 

To complete that thought: Only positive results are interesting.
For example if the command was to delete an entry which doesnt
exist there is no point in reporting that (or is there?).
OTOH, a successful delete is useful...

cheers,
jamal