Re: How to tell if a network interface was renamed (and from what)

On 11/18/23 19:15, Zhenlei Huang wrote:
> 
> 
>> On Nov 19, 2023, at 6:20 AM, Mina Galić <freebsd@igalic.co 
>> <mailto:freebsd@igalic.co>> wrote:
>>
>> Hi folks,
>>
>> Linux has an "easy" way of telling if an interface has been renamed.
>> See cloud-init's is_renamed function: 
>> https://github.com/canonical/cloud-init/blob/5496745b394f9b7b9eaf57fd619330d484ce2da8/cloudinit/net/__init__.py#L338-L350 <https://github.com/canonical/cloud-init/blob/5496745b394f9b7b9eaf57fd619330d484ce2da8/cloudinit/net/__init__.py#L338-L350>
>> This code reads /sys/class/net/<netif>/name_assign_type and if that is 
>> 3 or 4, it's been renamed.
>>
>> I can't even think of an sensible way of replicating that.
>> I can only think of terrible / wrong way of finding it out:
>>
>> dmesg | grep "changing name to '<new-netif>'"
>>
>> a less terrible method would be to check for, say:
>>
>> sysctl dev.<new-netif>.0.%driver
>>
>> if that fails, we probably have a renamed interface… but we don't know 
>> what it was renamed from, and this only works for *real* interfaces, 
>> not for cloned devices, or epairs.
>>
>> Now, ignoring my terrible hacky attempts at command line tooling, I 
>> would also happily accept a solution in C, which is fairly easily 
>> accessible from Python, and which we already use to figure out the 
>> uptime (or rather, the boottime): 
>> https://github.com/canonical/cloud-init/blob/5496745b394f9b7b9eaf57fd619330d484ce2da8/cloudinit/util.py#L2073-L2105 <https://github.com/canonical/cloud-init/blob/5496745b394f9b7b9eaf57fd619330d484ce2da8/cloudinit/util.py#L2073-L2105>
>>
>> Looking forward to reading your ideas.
> 
> FreeBSD currently does not preserve the old ( original ) name of 
> interfaces if it is renamed ( either physical or cloned ones ).
> While there's an attempt https://reviews.freebsd.org/D28247 
> <https://reviews.freebsd.org/D28247>  to get the device name (physical 
> ones) but it is not perfect and not completed.
> 
> So may I ask why you need to know if a network interface was renamed ?
> 

Just last week I found this quite a pain as well; once an interface has 
been renamed, if it's not a pseudo-interface with an obvious group 
there's no clear way, AFAICT, to determine which driver created it 
without perusing pciconf output or whatnot and hopefully being able to 
associate the NICs listed with the new names (easier when there's only 
one NIC, of course).  Kind of a pain when you're working on a remote 
machine that you're not at all familiar with.

Thanks,

Kyle Evans