netdev - Re: [patch net-next RFC 0/6] Add support for offloading packet-sampling

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Date:   Thu, 13 Oct 2016 07:49:07 -0400
From:   Jamal Hadi Salim <jhs@...atatu.com>
To:     Jiri Pirko <jiri@...nulli.us>,
        Roopa Prabhu <roopa@...ulusnetworks.com>
Cc:     netdev@...r.kernel.org, davem@...emloft.net, yotamg@...lanox.com,
        idosch@...lanox.com, eladr@...lanox.com, nogahf@...lanox.com,
        ogerlitz@...lanox.com, geert+renesas@...der.be,
        stephen@...workplumber.org, xiyou.wangcong@...il.com,
        linux@...ck-us.net
Subject: Re: [patch net-next RFC 0/6] Add support for offloading
 packet-sampling

On 16-10-13 04:48 AM, Jiri Pirko wrote:
> Thu, Oct 13, 2016 at 09:29:57AM CEST, roopa@...ulusnetworks.com wrote:
>> On 10/12/16, 5:41 AM, Jiri Pirko wrote:
>>> From: Jiri Pirko <jiri@...lanox.com>
>>>
[..]
>>
>> we spoke with yotam about this at netdev1.2. and also remember speaking about this on our switchdev calls:
>> Today our driver uses NFLOG to log packets to a netlink socket and hsflowd supported by the sflow
>> people (at http://www.sflow.net/) is capable of reading from a nflog socket. NFLOG has the required netlink
>> attribute markers for packet header/data (which we can possibly extend). We could also add nflog like action
>> in tc if needed.
>>
>> sflow agents like hsflowd are capable of sending packets to an external collector with the required sflow header.
>> Instead of re-inventing a new API for sflow, would be better to standardize/unify on existing mechanisms.
>>
>> Also, this patch series requires a new device to be created which can be avoided if we used
>> existing mechanisms like NFLOG.
>
> When I was first thinking about re-using NFLOG, it seemed like an
> abusal. We need to call it from driver directly, which sounds odd.
> However, since we use sample_packet_pack function to wrap it up, the
> NFLOG is called from the tc action code, it does not look bad.
> Yet still, this has nothing in common with netfilter, only using it's
> log facilities. That is odd.
>

Sorry, had not seen the code until now; helps me get perspective.
If you are going to require  netfilter just so you can do this - it
sounds so wrong (since you already provides a hook for tc offloading
into the switch for other functions).
Roopa, did you mean eth1 as the new device or did you mean just in
general config requiring a device to be specified or did you mean a new
cpu netdev being needed? I couldnt tell from the patch.

> I think that the IFE ways is way more clear and generic and not-abusing.
> However you are right the NFLOG way has advantage of existing user
> component. I'm not sure how to do this :(

Can you do NFLOG to user space without requiring netfilter compiled in?
One advantage with IFE is it is a wire protocol - so you can have the
sflow collector/aggregator sit on a different machine (for small cpu
switches makes sense). So modifying the sflow daemon to accept IFE
formatted data is an interesting!

cheers,
jamal