[lfs-support] "Interesting" Names

Dan McGhee beesnees at grm.net
Tue Nov 26 09:38:20 PST 2013


On 11/26/2013 11:23 AM, Bruce Dubbs wrote:
> Dan McGhee wrote:
>> On 11/26/2013 07:53 AM, William Harrington wrote:
>>> On Nov 25, 2013, at 8:06 PM, Dan McGhee wrote:
>>>
>>>> There were many allusions to the "new naming convention."  enpxx for
>>>> ethernet and wlpxx for wireless.  Where does this name convention
>>>> exist?  I remember that xlnglp posted about what he had discovered in
>>>> the "different" names, but I can't find what he wrote.  I don't
>>>> remember
>>>> if he had identified a source.
>>> Possibly it came from here:
>>> http://fedoraproject.org/wiki/Features/ConsistentNetworkDeviceNaming
>>>
>>> Check out biosdevname
>>>
>>> Sincerely,
>>>
>>> William Harrington
>> Thanks, William. That link led down an interesting path. It appears that
>> this "name thing" originated at Dell. I don't know if the fellow who
>> came up with the idea is a maintainer for UDEV or not. Anyway, The above
>> link led me to this:
>>
>> http://marc.info/?l=linux-hotplug&m=128892593821639&w=2
>>
>> It is an interesting discussion on how to implement or cancel the "name
>> thing" in udev. This, and William's suggestion, led me to "biosdevname."
>> It is a utility to take a kernel device name and return "the BIOS-given
>> name it 'should' be." (That from the biosdevname man page.)
>> [semi-rant]There is no indication of the identity of the "true BIOS name
>> giver."[/semi-rant]
>>
>> Also from the biosdevname man page:
>>
>>> The *physical* policy is the current default. However, when invoking
>>> biosdevname in udev rules, one should always specify the policy you
>>> want, as the default has changed over time.
>>> The *physical* policy uses the following scheme:
>>>
>>> em<port>[_<virtual instance>]
>>>      for embedded NICs p<slot>p<port>[_<virtual instance>]
>>>      for cards in PCI slots
>>> The
>>>      *all_ethN* policy makes a best guess at what the device order
>>>      should be, with embedded devices first, PCI cards in ascending
>>>      slot order, and ports in ascending PCI bus/device/function order
>>>      breadth-first. However, this policy /does/ not work if your PCI
>>>      devices are hot-plugged or hot-pluggable, including the virtual
>>>      functions on an SR-IOV device. In a hot-plug scenario, each
>>>      separate udev instance will be invoked in parallel, while the
>>>      device tree is still being populated with new devices. Each udev
>>>      instance will see a different PCI tree, and thus cannot provide
>>>      consistent enumeration. Use of this policy should be limited to
>>>      only scenarios where all PCI devices are present at boot (cold-plug).
>>>
>> So, it appears that this "name thing" is a "udev thing" and not a
>> "kernel thing." If my conclusions are correct, then I still wonder why
>> Alan's NIC, which is the same as mine, got a different name. The only
>> difference I know of so far is that he used LFS_SVN and I used LFS-7.4.
>> I'm discounting the kernel difference. I don't know if there's any
>> difference in results between UDEV-206 (LFS-7.4) and UDEV-208(LFS-SVN).
>> The only other possible difference is that Alan may have added "UDEV
>> Extras from BLFS.
> The difference could be the motherboard architecture or the slot the
> Ethernet is plugged into.
>
>> On the other hand, I can understand another possible difference unless I
>> don't understand what "hot-plug" means. To me it's the ability to "plug
>> something in" while the computer is running and have it work--much like
>> a USB device. If my NIC is hot-pluggable, I would have to open the
>> laptop case to remove it.
> There are such things as USB Ethernet adapters.  I'm not sure how useful
> they are today.  Perhaps some tablets have USB but not a Ethernet socket.
>
You're right, Bruce. I had my tongue in my cheek when I wrote what I did 
about "hotplugging." From reading that "policy statement" in the man 
page, I think my NIC should also be named "enpXsY" but it's "eth0." Like 
I've said, I really don't care. These are just dots that don't quite 
connect for me, and I don't like "loose dots" hanging around. :)

Dan




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