netdev - Re: [patch net-next 09/14] rocker: add rtnl ops for port mode [gs]etting

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Date:	Mon, 5 Oct 2015 10:00:06 -0700
From:	Scott Feldman <sfeldma@...il.com>
To:	Jiri Pirko <jiri@...nulli.us>
Cc:	Netdev <netdev@...r.kernel.org>,
	"David S. Miller" <davem@...emloft.net>,
	Ido Schimmel <idosch@...lanox.com>, eladr@...lanox.com,
	Thomas Graf <tgraf@...g.ch>,
	Alexei Starovoitov <ast@...mgrid.com>
Subject: Re: [patch net-next 09/14] rocker: add rtnl ops for port mode [gs]etting

On Mon, Oct 5, 2015 at 9:50 AM, Jiri Pirko <jiri@...nulli.us> wrote:
> Mon, Oct 05, 2015 at 06:37:20PM CEST, sfeldma@...il.com wrote:
>>On Mon, Oct 5, 2015 at 8:53 AM, Jiri Pirko <jiri@...nulli.us> wrote:
>>> Mon, Oct 05, 2015 at 05:41:29PM CEST, sfeldma@...il.com wrote:
>>>>On Sun, Oct 4, 2015 at 2:25 PM, Jiri Pirko <jiri@...nulli.us> wrote:
>>>>> From: Jiri Pirko <jiri@...lanox.com>
>>>>>
>>>>> Introduce a stub for allowing user to change rocker port world/mode.
>>>>> This is implemented using rtnl changelink op.
>>>>>
>>>>> Signed-off-by: Jiri Pirko <jiri@...lanox.com>
>>>>
>>>>[cut]
>>>>
>>>>> diff --git a/include/uapi/linux/if_link.h b/include/uapi/linux/if_link.h
>>>>> index 3a5f263..7da768e 100644
>>>>> --- a/include/uapi/linux/if_link.h
>>>>> +++ b/include/uapi/linux/if_link.h
>>>>> @@ -416,6 +416,17 @@ enum {
>>>>>  };
>>>>>  #define IFLA_GENEVE_MAX        (__IFLA_GENEVE_MAX - 1)
>>>>>
>>>>> +/* Rocker section */
>>>>> +enum {
>>>>> +       IFLA_ROCKER_UNSPEC,
>>>>> +       IFLA_ROCKER_MODE,
>>>>> +       __IFLA_ROCKER_MAX,
>>>>> +};
>>>>> +
>>>>> +#define IFLA_ROCKER_MAX        (__IFLA_ROCKER_MAX - 1)
>>>>> +
>>>>> +#define ROCKER_MODE_MAX 16
>>>>
>>>>Does this mean there is going to be a "ip link set dev DEV type rocker
>>>>mode MODE" command option?
>>>>
>>>>It doesn't seem right to be adding driver-specific IFLA_'s here.  I
>>>>think this sets bad precedence for other drivers to add their own
>>>>knobs without thinking about a generic shared mechanism.
>>>
>>> I understand you point. I somehow share it as well. But on the other
>>> hand, That is neat way to set mode of the port, and I cannot find other
>>> this nice.
>>>
>>>
>>>>
>>>>Actually, I don't see the point of letting the user dynamically change
>>>>the port mode.  I would prefer this knob be moved to qemu/rocker.  Let
>>>>the port mode be specified on device creation.
>>>
>>> Hmm, interesting, why? I find it great for user to be able to switch the
>>> port mode easily on the running system. It is a setting of a port.
>>> I don't see why this should be a hard-coded hw setting. We just have
>>> to find a way to expose this to user.
>>
>>You could just as easy restart the qemu session with different port
>>mode.  Even if rocker was a real device, I don't see (real) users
>>wanting to change the port mode at run-time.  It just doesn't seem
>>like a real-world scenario.   I know it's convenient for developers,
>
> We the hw-iface is already designed for on-fly changes.
> I'm convinced that this is one of the situation where we should not do
> stuff in HW just because we can. (Or we should do both).

I've used that argument myself for other things, such as the ageing
timer in rocker driver, so I agree with you on that point.

> We should develop in-kernel solution in order to wrap up HW functionality.
> Even if not easy. That is the purpose of rocker from day 1, and that is
> why we love it :)

Well then you need to define a generic interface for this concept of
changing port mode that's not rocker-specific.  What you have in
if_link.h is easy.  What's the not-easy solution?
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