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

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Message-ID: <CAE4R7bD=SFKgifw=xPudoFfHMcFAdGbVToQdvA9HrnFs3pjRYg@mail.gmail.com>
Date:	Mon, 5 Oct 2015 09:37:20 -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 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,
but a qemu knob is just as convenient.  Doing this in qemu will keep
the rocker driver less complicated, cleaner.
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