netdev - Re: [RFC PATCH bpf-next v2 0/4] Implement bpf queue/stack maps

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Message-ID: <975c5c3a-f24e-512d-7eb2-05e9c0fba612@polito.it>
Date:   Tue, 11 Sep 2018 09:48:57 -0500
From:   Mauricio Vasquez <mauricio.vasquez@...ito.it>
To:     Alexei Starovoitov <alexei.starovoitov@...il.com>
Cc:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Network Development <netdev@...r.kernel.org>,
        Joe Stringer <joe@...d.net.nz>
Subject: Re: [RFC PATCH bpf-next v2 0/4] Implement bpf queue/stack maps



On 09/10/2018 08:04 PM, Alexei Starovoitov wrote:
> On Fri, Sep 7, 2018 at 1:40 PM, Mauricio Vasquez
> <mauricio.vasquez@...ito.it> wrote:
>> I read the Joe's proposal and using that for this problem looks like a nice
>> solution.
>>
>> I think a good trade-off for now would be to go ahead with a queue/stack map
>> without preallocating support (or maybe include it having always in mind
>> that this issue has to be solved in the near future) and then, as a
>> separated work, try to use Joe's proposal in the map helpers.
>>
>> What do you think?
> the problem with such approach is that it would mean that
> non-prealloc stack/queue api will be different from future one
> after verifier will get smarter.
> The alternative would be to support by-value api only.
> Meaning let stack/queue support value_size = 1,2,4,8 byte only.
> Then bpf_push|pop_elem() helper will be by-value
> instead of returning a pointer.
> No rcu callback issues and implementation on the kernel
> side can be much simpler.
> I think simple array of value_size elems with head/tail indices
> will be enough.
> Once we have Joe's verifier improvements
> we can add alloc/free bpf object management facility
> and use 8-byte stack/queue mapas a stack of pointers.
> I think decoupling memory operations alloc/free from
> stack push/pop would be additional benefit of such design.
>
I agree, this suffices our requirements and avoid RCU issues.
Will spin a V3 implementing it this week.