Re: [virtio-dev] Re: net_failover slave udev renaming (was Re: [RFC PATCH net-next v6 4/4] netvsc: refactor notifier/event handling code to use the bypass framework)

[si-wei liu <si-wei.liu@oracle.com>]

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On 2/22/2019 7:14 AM, Michael S. Tsirkin wrote:
> On Thu, Feb 21, 2019 at 11:55:11PM -0800, si-wei liu wrote:
>>
>> On 2/21/2019 11:00 PM, Samudrala, Sridhar wrote:
>>>
>>> On 2/21/2019 7:33 PM, si-wei liu wrote:
>>>>
>>>> On 2/21/2019 5:39 PM, Michael S. Tsirkin wrote:
>>>>> On Thu, Feb 21, 2019 at 05:14:44PM -0800, Siwei Liu wrote:
>>>>>> Sorry for replying to this ancient thread. There was some remaining
>>>>>> issue that I don't think the initial net_failover patch got addressed
>>>>>> cleanly, see:
>>>>>>
>>>>>> https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1815268
>>>>>>
>>>>>> The renaming of 'eth0' to 'ens4' fails because the udev userspace was
>>>>>> not specifically writtten for such kernel automatic enslavement.
>>>>>> Specifically, if it is a bond or team, the slave would typically get
>>>>>> renamed *before* virtual device gets created, that's what udev can
>>>>>> control (without getting netdev opened early by the other part of
>>>>>> kernel) and other userspace components for e.g. initramfs,
>>>>>> init-scripts can coordinate well in between. The in-kernel
>>>>>> auto-enslavement of net_failover breaks this userspace convention,
>>>>>> which don't provides a solution if user care about consistent naming
>>>>>> on the slave netdevs specifically.
>>>>>>
>>>>>> Previously this issue had been specifically called out when IFF_HIDDEN
>>>>>> and the 1-netdev was proposed, but no one gives out a solution to this
>>>>>> problem ever since. Please share your mind how to proceed and solve
>>>>>> this userspace issue if netdev does not welcome a 1-netdev model.
>>>>> Above says:
>>>>>
>>>>>      there's no motivation in the systemd/udevd community at
>>>>>      this point to refactor the rename logic and make it work well with
>>>>>      3-netdev.
>>>>>
>>>>> What would the fix be? Skip slave devices?
>>>>>
>>>> There's nothing user can get if just skipping slave devices - the
>>>> name is still unchanged and unpredictable e.g. eth0, or eth1 the
>>>> next reboot, while the rest may conform to the naming scheme (ens3
>>>> and such). There's no way one can fix this in userspace alone - when
>>>> the failover is created the enslaved netdev was opened by the kernel
>>>> earlier than the userspace is made aware of, and there's no
>>>> negotiation protocol for kernel to know when userspace has done
>>>> initial renaming of the interface. I would expect netdev list should
>>>> at least provide the direction in general for how this can be
>>>> solved...
>
> I was just wondering what did you mean when you said
> "refactor the rename logic and make it work well with 3-netdev" -
> was there a proposal udev rejected?
No. I never believed this particular issue can be fixed in userspace 
alone. Previously someone had said it could be, but I never see any work 
or relevant discussion ever happened in various userspace communities 
(for e.g. dracut, initramfs-tools, systemd, udev, and NetworkManager). 
IMHO the root of the issue derives from the kernel, it makes more sense 
to start from netdev, work out and decide on a solution: see what can be 
done in the kernel in order to fix it, then after that engage userspace 
community for the feasibility...

> Anyway, can we write a time diagram for what happens in which order that
> leads to failure?  That would help look for triggers that we can tie
> into, or add new ones.
>

See attached diagram.

>
>
>
>
>>> Is there an issue if slave device names are not predictable? The user/admin scripts are expected
>>> to only work with the master failover device.
>> Where does this expectation come from?
>>
>> Admin users may have ethtool or tc configurations that need to deal with
>> predictable interface name. Third-party app which was built upon specifying
>> certain interface name can't be modified to chase dynamic names.
>>
>> Specifically, we have pre-canned image that uses ethtool to fine tune VF
>> offload settings post boot for specific workload. Those images won't work
>> well if the name is constantly changing just after couple rounds of live
>> migration.
> It should be possible to specify the ethtool configuration on the
> master and have it automatically propagated to the slave.
>
> BTW this is something we should look at IMHO.
I was elaborating a few examples that the expectation and assumption 
that user/admin scripts only deal with master failover device is 
incorrect. It had never been taken good care of, although I did try to 
emphasize it from the very beginning.

Basically what you said about propagating the ethtool configuration down 
to the slave is the key pursuance of 1-netdev model. However, what I am 
seeking now is any alternative that can also fix the specific udev 
rename problem, before concluding that 1-netdev is the only solution. 
Generally a 1-netdev scheme would take time to implement, while I'm 
trying to find a way out to fix this particular naming problem under 
3-netdev.

>
>>> Moreover, you were suggesting hiding the lower slave devices anyway. There was some discussion
>>> about moving them to a hidden network namespace so that they are not visible from the default namespace.
>>> I looked into this sometime back, but did not find the right kernel api to create a network namespace within
>>> kernel. If so, we could use this mechanism to simulate a 1-netdev model.
>> Yes, that's one possible implementation (IMHO the key is to make 1-netdev
>> model as much transparent to a real NIC as possible, while a hidden netns is
>> just the vehicle). However, I recall there was resistance around this
>> discussion that even the concept of hiding itself is a taboo for Linux
>> netdev. I would like to summon potential alternatives before concluding
>> 1-netdev is the only solution too soon.
>>
>> Thanks,
>> -Siwei
> Your scripts would not work at all then, right?
At this point we don't claim images with such usage as SR-IOV live 
migrate-able. We would flag it as live migrate-able until this ethtool 
config issue is fully addressed and a transparent live migration 
solution emerges in upstream eventually.


Thanks,
-Siwei
>
>
>>>> -Siwei
>>>>
>>>>
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[-- Attachment #2: net_failover_rename_race.txt --]
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  net_failover(kernel)                            |    network.service (user)    |          systemd-udevd (user)
--------------------------------------------------+------------------------------+--------------------------------------------
(standby virtio-net and net_failover              |                              |
devices created and initialized,                  |                              |
i.e. virtnet_probe()->                            |                              |
       net_failover_create()                      |                              |
was done.)                                        |                              |
                                                  |                              |
                                                  |  runs `ifup ens3' ->         |
                                                  |    ip link set dev ens3 up   |
net_failover_open()                               |                              |
  dev_open(virtnet_dev)                           |                              |
    virtnet_open(virtnet_dev)                     |                              |
  netif_carrier_on(failover_dev)                  |                              |
  ...                                             |                              |
                                                  |                              |
(VF hot plugged in)                               |                              |
ixgbevf_probe()                                   |                              |
 register_netdev(ixgbevf_netdev)                  |                              |
  netdev_register_kobject(ixgbevf_netdev)         |                              |
   kobject_add(ixgbevf_dev)                       |                              |
    device_add(ixgbevf_dev)                       |                              |
     kobject_uevent(&ixgbevf_dev->kobj, KOBJ_ADD) |                              |
      netlink_broadcast()                         |                              |
  ...                                             |                              |
  call_netdevice_notifiers(NETDEV_REGISTER)       |                              |
   failover_event(..., NETDEV_REGISTER, ...)      |                              |
    failover_slave_register(ixgbevf_netdev)       |                              |
     net_failover_slave_register(ixgbevf_netdev)  |                              |
      dev_open(ixgbevf_netdev)                    |                              |
                                                  |                              |
                                                  |                              |
                                                  |                              |   received ADD uevent from netlink fd
                                                  |                              |   ...
                                                  |                              |   udev-builtin-net_id.c:dev_pci_slot()
                                                  |                              |   (decided to renamed 'eth0' )
                                                  |                              |     ip link set dev eth0 name ens4
(dev_change_name() returns -EBUSY as              |                              |
ixgbevf_netdev->flags has IFF_UP)                 |                              |
                                                  |                              |