Subject: Re: [net-next PATCH v3 00/12] Flow API

From: John Fastabend <[email-masked]>
Date: Thu, 22 Jan 2015 08:58:07 -0800

On 01/22/2015 07:13 AM, Thomas Graf wrote:
> On 01/22/15 at 10:00am, Jamal Hadi Salim wrote:
>> On 01/22/15 09:00, Pablo Neira Ayuso wrote:
>>
>>>

I'll try to unify the threads here

>>> +/* rocker specific action definitions */
>>> +struct net_flow_action_arg rocker_set_group_id_args[] = {
>>> +       {
>>> +               .name = "group_id",
>>> +               .type = NFL_ACTION_ARG_TYPE_U32,
>>> +               .value_u32 = 0,
>>> +       },
>>>

In response to Pablo's observation,

Correct this is fully exposed to user space, but it is also self
contained inside the API meaning I can learn when to use it and what it
does by looking at the other operations tables the table graph and
supported headers. The assumption I am making that is not in the API
explicitly yet. Is that actions named "set_field_name" perform the
set operation on that field. We can and plan to extend the API to make
this assumption explicit in the API.

In this case I can "learn" that I can match on group_id in some tables
and then use the above action to set the group_id in others.

>>> that is retrieved via ndo_flow_get_actions and fully exposed to
>>> userspace.
>>>
>>
>> My main concern is along similar lines (I did express it earlier and
>> I think Jiri chimed in as well).
>> The API exposes direct access to hardware. I am sure this was a result
>> of trying to replace the ethtool interface (which was primitive).
>> By providing vendors direct access to the hardware - they do not need
>> to use any traditional Linux tooling/APIs.
>
> I don't follow this. John's proposal allows to decide on a case by
> case basis what we want to export. Just like with ethtool or
> RTNETLINK. There is no direct access to hardware. A user can only
> configure what is being exposed by the kernel.
>
> Pablo raises an interesting point though. How do we handle unique
> features like Rocker groups.
>
> Maybe Jiri and Scott can chime in and describe if we can map this to
> something more generic and avoid exporting anything Rocker specific.
>

Even though its a detail of the rocker world its easy enough for a
program on top of the API to learn how it works.

So in the rocker switch case if I want to rewrite an eth_dst adress I
have a  couple choices. I can set the group_id in one of the tables
that support setting the group_id and then do the rewrite in one of the
tables that supports matching on group_id and setting the eth_dst mac.
The "choice" I make is a policy IMO and I don't want to hard code logic
in the kernel that picks tables and decides things like what should I
do if table x is full but table y could also be used should I overflow
into table y? Or  is table y reserved for some other network function?
etc.

There are some actions and metadata though that _need_ to be
standardized. These are the metadata that is used outside the API. For
example ingress_port is metadata that is set outside the tables.
Similarly set_egress_port and set_egress_queue provide the forwarding
and queueing fields. No matter how hard you look at the model from the
API you can not learn how these are used.

> What would a rocker group map to in the tc world?

In the 'tc' world I would guess the easiest thing to do is simply bind
a 'tc' qdisc to the ACL table. It seems a good first approximation of
how to make this work. But the rocker world doesn't yet have any QOS so
it makes it difficult to "offload" anything but the fifo qdiscs.

>
>> I see this as a gaping hole
>> for vendor SDKs with their own definitions of their own hardware that
>> doesnt work with anyone else. i.e it seems to standardize proprietary
>> interfaces. Maybe thats what Pablo is alluding to.
>
> I will be the first to root for rejection if such patches appear.
>

Is it problematic if users define some unique header here and then
provide actions to set/pop/push/get operations on it?

For me this seems perfectly reasonable. We can pull it out of hardware
or a database in libvirt perhaps then feed it back into Linux nft,
ebpf, tc u32_filter, to create a unified view. I think ebpf, nft, and
u32 have been all about supporting vendor specific protocols?

I must be missing the point about proprietary interfaces. The FLOW API
would be the interface and if we create interesting tools/systems around
it and integration with other Linux sub-systems by choosing to use a
proprietary SDK you lose the goodness.

.John

-- 
John Fastabend         Intel Corporation