Re: [RFC] longer netdev names proposal

[Jiri Pirko <jiri@resnulli.us>]

Thu, Jun 27, 2019 at 07:14:31PM CEST, dsahern@gmail.com wrote:
>On 6/27/19 3:43 AM, Jiri Pirko wrote:
>> Hi all.
>> 
>> In the past, there was repeatedly discussed the IFNAMSIZ (16) limit for
>> netdevice name length. Now when we have PF and VF representors
>> with port names like "pfXvfY", it became quite common to hit this limit:
>> 0123456789012345
>> enp131s0f1npf0vf6
>> enp131s0f1npf0vf22
>
>QinQ (stacked vlans) is another example.

There are more usecases for this, yes.


>
>> 
>> Since IFLA_NAME is just a string, I though it might be possible to use
>> it to carry longer names as it is. However, the userspace tools, like
>> iproute2, are doing checks before print out. So for example in output of
>> "ip addr" when IFLA_NAME is longer than IFNAMSIZE, the netdevice is
>> completely avoided.
>> 
>> So here is a proposal that might work:
>> 1) Add a new attribute IFLA_NAME_EXT that could carry names longer than
>>    IFNAMSIZE, say 64 bytes. The max size should be only defined in kernel,
>>    user should be prepared for any string size.
>> 2) Add a file in sysfs that would indicate that NAME_EXT is supported by
>>    the kernel.
>
>no sysfs files.
>
>Johannes added infrastructure to retrieve the policy. That is a more
>flexible and robust option for determining what the kernel supports.

Sure, udev can query rtnetlink. I just proposed it as an option, anyway,
it's implementation detail.


>
>
>> 3) Udev is going to look for the sysfs indication file. In case when
>>    kernel supports long names, it will do rename to longer name, setting
>>    IFLA_NAME_EXT. If not, it does what it does now - fail.
>> 4) There are two cases that can happen during rename:
>>    A) The name is shorter than IFNAMSIZ
>>       -> both IFLA_NAME and IFLA_NAME_EXT would contain the same string:
>>          original IFLA_NAME     = eth0
>>          original IFLA_NAME_EXT = eth0
>>          renamed  IFLA_NAME     = enp5s0f1npf0vf1
>>          renamed  IFLA_NAME_EXT = enp5s0f1npf0vf1
>>    B) The name is longer tha IFNAMSIZ
>>       -> IFLA_NAME would contain the original one, IFLA_NAME_EXT would 
>>          contain the new one:
>>          original IFLA_NAME     = eth0
>>          original IFLA_NAME_EXT = eth0
>>          renamed  IFLA_NAME     = eth0
>>          renamed  IFLA_NAME_EXT = enp131s0f1npf0vf22
>
>so kernel side there will be 2 names for the same net_device?

Yes. However, updated tools (which would be eventually all) are going to
show only the ext one.



>
>> 
>> This would allow the old tools to work with "eth0" and the new
>> tools would work with "enp131s0f1npf0vf22". In sysfs, there would
>> be symlink from one name to another.
>
>I would prefer a solution that does not rely on sysfs hooks.

Please note that this /sys/class/net/ifacename dirs are already created.
What I propose is to have symlink from ext to the short name or vice
versa. The solution really does not "rely" on this...


>
>>       
>> Also, there might be a warning added to kernel if someone works
>> with IFLA_NAME that the userspace tool should be upgraded.
>
>that seems like spam and confusion for the first few years of a new api.

Spam? warn_once?


>
>> 
>> Eventually, only IFLA_NAME_EXT is going to be used by everyone.
>> 
>> I'm aware there are other places where similar new attribute
>> would have to be introduced too (ip rule for example).
>> I'm not saying this is a simple work.
>> 
>> Question is what to do with the ioctl api (get ifindex etc). I would
>> probably leave it as is and push tools to use rtnetlink instead.
>
>The ioctl API is going to be a limiter here. ifconfig is still quite
>prevalent and net-snmp still uses ioctl (as just 2 common examples).
>snmp showing one set of names and rtnetlink s/w showing another is going
>to be really confusing.

I don't see other way though, do you? The ioctl names are unextendable :/