Message-ID: <4c478222-95fd-31f9-f8b7-9237ffe70c33@oracle.com>
Date:   Wed, 6 Mar 2019 00:20:54 -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 11:23 PM, Michael S. Tsirkin wrote:
> On Tue, Mar 05, 2019 at 11:15:06PM -0800, si-wei liu wrote:
>>
>> On 3/5/2019 10:43 PM, Michael S. Tsirkin wrote:
>>> On Tue, Mar 05, 2019 at 04:51:00PM -0800, si-wei liu wrote:
>>>> 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.
>>> These scripts then would be broken  on any box with multiple interfaces
>>> since not all of these would have carrier.
>> Consider a script executing `ifconfig ... up' and once succeeds runs tcpdump
>> or some other command relying on UP interface. It's quite common that those
>> scripts don't check the UP flag but instead just rely on the well-known fact
>> that the command exits with 0 meaning the interface should be UP. This
>> change might well break scripts of that kind.
> I am sorry I don't get it. Could you give an example
> of a script that works now but would be broken?

https://github.com/torvalds/linux/blob/master/tools/testing/selftests/net/netdevice.sh#L27
https://github.com/WPO-Foundation/wptagent/blob/master/internal/adb.py#L443
https://github.com/openstack/steth/blob/master/steth/agent/api.py#L134

There are more if you keep searching.

-Siwei

>
>
>>>
>>>> It doesn't look to be a reliable
>>>> way of prohibit userspace from operating against slaves.
>>>>
>>>> -Siwei
>>>>
>>>>
>>> This does not mean we shouldn't make an effort to disable broken
>>> configurations.
>>>
>>> I am not arguing against your patch. Not at all. I see better
>>> hiding of slaves as a separate enhancement.
>> I understand, but my point is we should try to minimize unnecessary side
>> impact to the current usage for whatever "hiding" effort we can make. It's
>> hard to find a tradeoff sometimes.
> Yes if some userspace made an assumption and it worked, we should keep
> it working I think. I don't necessarily agree we should worry too much
> about theoretical issues. In half a year since the feature got merged
> it's unlikely there are millions of slightly different scripts using it.
>
>>>
>>> Acked-by: Michael S. Tsirkin <mst@...hat.com>
>>>
>>>
>> Thank you.
>>
>> -Siwei

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