Provide ability to change default netdev name?

Provide ability to change default netdev name?

[Ben Greear]

The latest udev in Fedora 19 (and perhaps elsewhere) will no longer
implement rules that rename an interface from ethX to ethY.  Nor
wlanX or other 'kernel namespaces'.  The Fedora udev developers do not seem
interested in changing this back to the old behaviour, evidently they
had a hard time implementing it properly.

This effectively makes it impossible to have network device names of ethX
consistent across reboots in systems with multiple NICs and/or drivers.

One way to work around this would be allow the kernel to use a different
default netdev name (for instance, keth%d).  I'm thinking this would be
configured as a kernel command line argument.  Then, a small change to udev/systemd to
make the 'kernel namespaces' configurable by letting it understand this new kernel
command line argument should resolve the problem.

Does this sound like something that could be accepted upstream?

Thanks,
Ben

-- 
Ben Greear <greearb@candelatech.com>
Candela Technologies Inc  http://www.candelatech.com

Re: Provide ability to change default netdev name?

[Ben Hutchings]

On Fri, 2013-08-16 at 15:14 -0700, Ben Greear wrote:
> The latest udev in Fedora 19 (and perhaps elsewhere) will no longer
> implement rules that rename an interface from ethX to ethY.  Nor
> wlanX or other 'kernel namespaces'.  The Fedora udev developers do not seem
> interested in changing this back to the old behaviour, evidently they
> had a hard time implementing it properly.

There is an inherent problem that a new device can appear at any time
under the exact name udev is trying to rename to.  I expect it is
possible to do this properly but may be quite difficult to eliminate the
possibility of deadlock.

Still, if udev actively refuses to use the 'kernel namespaces' (rather
than just being configured not to), that would be a bug.

> This effectively makes it impossible to have network device names of ethX
> consistent across reboots in systems with multiple NICs and/or drivers.
> 
> One way to work around this would be allow the kernel to use a different
> default netdev name (for instance, keth%d).  I'm thinking this would be
> configured as a kernel command line argument.  Then, a small change to udev/systemd to
> make the 'kernel namespaces' configurable by letting it understand this new kernel
> command line argument should resolve the problem.
> 
> Does this sound like something that could be accepted upstream?

This sounds completely ridiculous.

Ben.

-- 
Ben Hutchings, Staff Engineer, Solarflare
Not speaking for my employer; that's the marketing department's job.
They asked us to note that Solarflare product names are trademarked.

Re: Provide ability to change default netdev name?

[Ben Greear]

On 08/16/2013 04:41 PM, Ben Hutchings wrote:
> On Fri, 2013-08-16 at 15:14 -0700, Ben Greear wrote:
>> The latest udev in Fedora 19 (and perhaps elsewhere) will no longer
>> implement rules that rename an interface from ethX to ethY.  Nor
>> wlanX or other 'kernel namespaces'.  The Fedora udev developers do not seem
>> interested in changing this back to the old behaviour, evidently they
>> had a hard time implementing it properly.
>
> There is an inherent problem that a new device can appear at any time
> under the exact name udev is trying to rename to.  I expect it is
> possible to do this properly but may be quite difficult to eliminate the
> possibility of deadlock.
>
> Still, if udev actively refuses to use the 'kernel namespaces' (rather
> than just being configured not to), that would be a bug.

I agree, but the Fedora udev developers do not.  I'm not sure
if other distros will follow or not.

>> This effectively makes it impossible to have network device names of ethX
>> consistent across reboots in systems with multiple NICs and/or drivers.
>>
>> One way to work around this would be allow the kernel to use a different
>> default netdev name (for instance, keth%d).  I'm thinking this would be
>> configured as a kernel command line argument.  Then, a small change to udev/systemd to
>> make the 'kernel namespaces' configurable by letting it understand this new kernel
>> command line argument should resolve the problem.
>>
>> Does this sound like something that could be accepted upstream?
>
> This sounds completely ridiculous.

Yeah, seems lame to hack around funky user-space, but
if udev folks will truly not fix this, then life is
going to suck for users wanting to use 'ethX' naming
schemes for their network devices.

Thanks,
Ben


-- 
Ben Greear <greearb@candelatech.com>
Candela Technologies Inc  http://www.candelatech.com