netdev - Re: [RFC PATCH net-next] failover: allow name change on IFF

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Date:   Tue, 5 Mar 2019 16:20:50 -0800
From:   si-wei liu <si-wei.liu@...cle.com>
To:     "Michael S. Tsirkin" <mst@...hat.com>
Cc:     Stephen Hemminger <stephen@...workplumber.org>,
        Sridhar Samudrala <sridhar.samudrala@...el.com>,
        Jakub Kicinski <kubakici@...pl>, Jiri Pirko <jiri@...nulli.us>,
        David Miller <davem@...emloft.net>,
        Netdev <netdev@...r.kernel.org>,
        virtualization@...ts.linux-foundation.org, liran.alon@...cle.com,
        boris.ostrovsky@...cle.com, vijay.balakrishna@...cle.com
Subject: Re: [RFC PATCH net-next] failover: allow name change on IFF_UP slave
 interfaces



On 3/5/2019 4:06 PM, Michael S. Tsirkin wrote:
> On Tue, Mar 05, 2019 at 11:35:50AM -0800, si-wei liu wrote:
>>
>> On 3/5/2019 11:24 AM, Stephen Hemminger wrote:
>>> On Tue, 5 Mar 2019 11:19:32 -0800
>>> si-wei liu <si-wei.liu@...cle.com> wrote:
>>>
>>>>> I have a vague idea: would it work to *not* set
>>>>> IFF_UP on slave devices at all?
>>>> Hmm, I ever thought about this option, and it appears this solution is
>>>> more invasive than required to convert existing scripts, despite the
>>>> controversy of introducing internal netdev state to differentiate user
>>>> visible state. Either we disallow slave to be brought up by user, or to
>>>> not set IFF_UP flag but instead use the internal one, could end up with
>>>> substantial behavioral change that breaks scripts. Consider any admin
>>>> script that does `ip link set dev ... up' successfully just assumes the
>>>> link is up and subsequent operation can be done as usual.
> How would it work when carrier is off?
>
>> While it *may*
>>>> work for dracut (yet to be verified), I'm a bit concerned that there are
>>>> more scripts to be converted than those that don't follow volatile
>>>> failover slave names. It's technically doable, but may not worth the
>>>> effort (in terms of porting existing scripts/apps).
>>>>
>>>> Thanks
>>>> -Siwei
>>> Won't work for most devices.  Many devices turn off PHY and link layer
>>> if not IFF_UP
>> True, that's what I said about introducing internal state for those driver
>> and other kernel component. Very invasive change indeed.
>>
>> -Siwei
> Well I did say it's vague.
> How about hiding IFF_UP from dev_get_flags (and probably
> __dev_change_flags)?
>
Any different? This has small footprint for the kernel change for sure, 
while the discrepancy is still there. Anyone who writes code for IFF_UP 
will not notice IFF_FAILOVER_SLAVE.

Not to mention more userspace "fixup" work has to be done due to this 
change.

-Siwei