Re: [RFC 0/3] Adding config get/set to devlink

[Roopa Prabhu <roopa@cumulusnetworks.com>]

On Thu, Oct 12, 2017 at 12:20 PM, Florian Fainelli <f.fainelli@gmail.com> wrote:
> On 10/12/2017 12:06 PM, David Miller wrote:
>> From: Florian Fainelli <f.fainelli@gmail.com>
>> Date: Thu, 12 Oct 2017 08:43:59 -0700
>>
>>> Once we move ethtool (or however we name its successor) over to
>>> netlink there is an opportunity for accessing objects that do and do
>>> not have a netdevice representor today (e.g: management ports on
>>> switches) with the same interface, and devlink could be used for
>>> that.
>>
>> That is an interesting angle for including this in devlink.
>>
>> I'm not so sure what to do about this.
>>
>> One suggestion is that devlink is used for getting ethtool stats for
>> objects lacking netdev representor's, and a new genetlink family is
>> used for netdev based ethtool.
>
> Right, I was also thinking along those lines that we we would have a new
> generic netlink family for ethtool to support ethtool over netlink.

new api is fine by me. The reason for suggesting devlink was because
some of the devlink
port_* ops are close to ethtool ops that can operate on a port/netdev.
eg split_port could be a netdev operation
unless you want to split before the netdev is created.

There are some ops in devlink which are global hw parameters and not
specific to a port, those fit perfectly with
devlinks original goal.


>
>>
>> I think it's important that we don't expand the scope of devlink
>> beyond what it was originally designed for.
>
> It seems to me like devlink is well defined in what it is not for: it is
> not meant to be used for any object that is/has a net_device, but it is
> not well defined for what it can offer to these non network devices. For
> instance, we have a tremendous amount of operations that are extremely
> specific to its single user(s) such as mlx5 and mlxsw.
>
> For instance, I am not sure how the buffer reservation scheme can be
> generalized, and this is always the tricky part with a single user
> facility in that you try to generalize the best you can based on the HW
> you know. This is not a criticism or meant to be anything negative, this
> just happens to be the case, and we did not have anything better.
>
> So maybe the first thing is to clarify what devlink operations can and
> should be and what they are absolutely not allowed to cover. We should
> also clarify whether a generic set/get that Steven is proposing is
> something that we tolerate, or whether there should be specific function
> pointers implemented for each attribute, which would be more in line
> with what has been done thus far.
> --
> Florian