netdev - Re: [PATCH net-next v8 09/15] p4tc: add template pipeline create, get, update, delete

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Date: Mon, 20 Nov 2023 10:20:46 -0800
From: David Ahern <dsahern@...nel.org>
To: Jamal Hadi Salim <jhs@...atatu.com>, Jiri Pirko <jiri@...nulli.us>
Cc: netdev@...r.kernel.org, deb.chatterjee@...el.com,
 anjali.singhai@...el.com, namrata.limaye@...el.com, tom@...anda.io,
 mleitner@...hat.com, Mahesh.Shirshyad@....com, tomasz.osinski@...el.com,
 xiyou.wangcong@...il.com, davem@...emloft.net, edumazet@...gle.com,
 kuba@...nel.org, pabeni@...hat.com, vladbu@...dia.com, horms@...nel.org,
 daniel@...earbox.net, bpf@...r.kernel.org, khalidm@...dia.com,
 toke@...hat.com, mattyk@...dia.com, David Ahern <dsahern@...il.com>,
 Stephen Hemminger <stephen@...workplumber.org>
Subject: Re: [PATCH net-next v8 09/15] p4tc: add template pipeline create,
 get, update, delete

On 11/17/23 4:09 AM, Jamal Hadi Salim wrote:
>>> diff --git a/include/uapi/linux/p4tc.h b/include/uapi/linux/p4tc.h
>>> index ba32dba66..4d33f44c1 100644
>>> --- a/include/uapi/linux/p4tc.h
>>> +++ b/include/uapi/linux/p4tc.h
>>> @@ -2,8 +2,71 @@
>>> #ifndef __LINUX_P4TC_H
>>> #define __LINUX_P4TC_H
>>>
>>> +#include <linux/types.h>
>>> +#include <linux/pkt_sched.h>
>>> +
>>> +/* pipeline header */
>>> +struct p4tcmsg {
>>> +      __u32 pipeid;
>>> +      __u32 obj;
>>> +};
>>
>> I don't follow. Is there any sane reason to use header instead of normal
>> netlink attribute? Moveover, you extend the existing RT netlink with
>> a huge amout of p4 things. Isn't this the good time to finally introduce
>> generic netlink TC family with proper yaml spec with all the benefits it
>> brings and implement p4 tc uapi there? Please?
>>

There is precedence (new netdev APIs) to move new infra to genl, but it
is not clear to me if extending existing functionality should fall into
that required conversion.

> 
> Several reasons:
> a) We are similar to current tc messaging with the subheader being
> there for multiplexing.
> b) Where does this leave iproute2? +Cc David and Stephen. Do other
> generic netlink conversions get contributed back to iproute2?
> c) note: Our API is CRUD-ish instead of RPC(per generic netlink)
> based. i.e you have:
>  COMMAND <PATH/TO/OBJECT> [optional data]  so we can support arbitrary
> P4 programs from the control plane.
> d) we have spent many hours optimizing the control to the kernel so i
> am not sure what it would buy us to switch to generic netlink..
>