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

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Date:   Thu, 12 Oct 2017 08:43:59 -0700
From:   Florian Fainelli <f.fainelli@...il.com>
To:     Jiri Pirko <jiri@...nulli.us>,
        Roopa Prabhu <roopa@...ulusnetworks.com>
CC:     Steve Lin <steven.lin1@...adcom.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        Jiri Pirko <jiri@...lanox.com>,
        "davem@...emloft.net" <davem@...emloft.net>,
        michael.chan@...adcom.com, linux-pci@...r.kernel.org,
        "John W. Linville" <linville@...driver.com>, gospo@...adcom.com
Subject: Re: [RFC 0/3] Adding config get/set to devlink

On October 12, 2017 8:04:19 AM PDT, Jiri Pirko <jiri@...nulli.us> wrote:
>Thu, Oct 12, 2017 at 04:46:24PM CEST, roopa@...ulusnetworks.com wrote:
>>On Thu, Oct 12, 2017 at 7:40 AM, Jiri Pirko <jiri@...nulli.us> wrote:
>>> Thu, Oct 12, 2017 at 04:35:10PM CEST, roopa@...ulusnetworks.com
>wrote:
>>>>On Thu, Oct 12, 2017 at 6:34 AM, Steve Lin
><steven.lin1@...adcom.com> wrote:
>>>>> Adds a devlink command for getting & setting device configuration
>>>>> parameters, and enumerates a bunch of those parameters as devlink
>>>>> attributes.  Also introduces an attribute that can be set by a
>>>>> driver to indicate that the config change doesn't take effect
>>>>> until the next restart (as in the case of the bnxt driver changes
>>>>> in this patchset, for which all the configuration changes affect
>NVM
>>>>> only, and aren't loaded until the next restart.)
>>>>>
>>>>> bnxt driver patches make use of these new devlink cmds/attributes.
>>>>>
>>>>> Steve Lin (3):
>>>>>   devlink: Add config parameter get/set operations
>>>>>   bnxt: Move generic devlink code to new file
>>>>>   bnxt: Add devlink support for config get/set
>>>>>
>>>>
>>>>Is the goal here to move all ethtool operations to devlink (I saw
>some
>>>>attrs related to speed etc). ?.
>>>>We do need to move ethtool attrs to netlink and devlink is a good
>>>>place (and of-course leave the current ethtool api around for
>backward
>>>>compatibility).
>>>
>>> We need to make sure we are not moving things to devlink which don't
>>> belong there. All options that use "netdev" as a handle should go
>into
>>> rtnetlink instead.
>>>
>>
>>Any reason you want to keep that restriction ?.
>>FWIS, devlink is a driver api just like ethtool is.
>>and ethtool needs to move to netlink soon...and It would be better to
>>not put the rtnl_lock burden on ethtool driver operations. Instead of
>>adding yet another driver api, extending devlink seems like a great
>>fit to me.
>
>Hmm, the original purpose of devlink was to obtain iface for things
>that
>could not use "netdev" as a handle. I try to stick with it as we
>already
>have iface for things that could use "netdev" as a handle - rtnetlink.
>
>Not sure we want to go this way and add "netdev"-handle things into
>devlink. Thoughts?

In the current situation where we have ethtool and devlink operating separately on different objects as entry points to the kernel, I agree with that design.

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.

In terms of compatibility though we should have a pseudo generic layer that can take ethtool ioctl() and transform that into a netlink message and then call back down to drivers with the existing ethtool_ops that are implemented. It is reasonably simple to use coccinelle to update these ethtool_ops with possibly updated signatures to support netlink attributes and whatnot, but forcing drivers to quit doing ethtool_ops entitely and implement new sets of "ethtool over netlink" ops is a non starter IMHO.

-- 
Florian