Re: [RFC] longer netdev names proposal

[David Ahern <dsahern@gmail.com>]

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.

> 
> 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.


> 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?

> 
> 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.

>       
> 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.

> 
> 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.