Date:   Thu, 27 Jun 2019 11:12:54 -0500
From:   Dan Williams <dcbw@...hat.com>
To:     Stephen Hemminger <stephen@...workplumber.org>,
        Jiri Pirko <jiri@...nulli.us>
Cc:     netdev@...r.kernel.org, davem@...emloft.net,
        jakub.kicinski@...ronome.com, sthemmin@...rosoft.com,
        dsahern@...il.com, mlxsw@...lanox.com
Subject: Re: [RFC] longer netdev names proposal

On Thu, 2019-06-27 at 08:29 -0700, Stephen Hemminger wrote:
> On Thu, 27 Jun 2019 11:43:27 +0200
> Jiri Pirko <jiri@...nulli.us> 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
> > 
> > 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.
> > 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

It makes me a bit uncomfortable to allow IFLA_NAME and IFLA_NAME_EXT to
be completely different. That sounds like a big source of confusion and
debugging problems in production.

Dan

> > 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.
> >       
> > Also, there might be a warning added to kernel if someone works
> > with IFLA_NAME that the userspace tool should be upgraded.
> > 
> > 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.
> > 
> > Any ideas why this would not work? Any ideas how to solve this
> > differently?
> > 
> > Thanks!
> > 
> > Jiri
> >      
> 
> I looked into this in the past, but then rejected it because
> there are so many tools that use names, not just iproute2.
> Plus long names are very user unfriendly.

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