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

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Date:   Tue, 5 Mar 2019 16:51:00 -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 4:36 PM, Michael S. Tsirkin wrote:
> On Tue, Mar 05, 2019 at 04:20:50PM -0800, si-wei liu wrote:
>>
>> 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
>>
>>
> Point is it's ok since most userspace should just ignore slaves
> - hopefully it will just ignore it since it already
> ignores interfaces that are down.
Admin script thought the interface could be bright up and do further 
operations without checking the UP flag. It doesn't look to be a 
reliable way of prohibit userspace from operating against slaves.

-Siwei