Re: Specifying names for tap interfaces

[Darren Reed <darrenr%netbsd.org@localhost>]

On 21/06/2012 7:17 AM, Roger Pau Monné wrote:
> On Wed, Jun 20, 2012 at 9:49 PM, Darren Reed <darrenr%netbsd.org@localhost> 
> wrote:
>> On 21/06/2012 6:08 AM, Manuel Bouyer wrote:
>>> On Thu, Jun 21, 2012 at 06:03:21AM +1000, Darren Reed wrote:
>>>> On 21/06/2012 5:34 AM, Manuel Bouyer wrote:
>>>>> On Thu, Jun 21, 2012 at 05:08:13AM +1000, Darren Reed wrote:
>>>>>> No, this is not the right approach and I don't think that a short cut
>>>>>> solution like this belongs in NetBSD.
>>>>>>
>>>>>> As you noticed, this requires changes to other utilities in order to 
>>>>>> work.
>>>>>
>>>>> beside ifconfig, I'm not sure.
>>>>>
>>>>>>
>>>>>> If your project requires any changes to brconfig, netstat, ifconfig, ipf,
>>>>>> npf, tcpdump, etc, then you've got the wrong solution in hand. Each 
>>>>>> network
>>>>>> interface should have one name and one name only as far as userland is
>>>>>> concerned. If there are userland programs (aside from device management)
>>>>>
>>>>> I'm not happy with the "one name and one name only".
>>>>
>>>> Why aren't you happy?
>>>>
>>>>> I think some use case
>>>>> will want the name, some other will want the alias (and you may need both
>>>>> at the same time).
>>>>
>>>> Such as...?
>>>
>>> I saw some people being unhappy with the idea of interface rename
>>> ("once you're renamed it to foobar you don't know anymore if it's a
>>> wm(4) or a tap(4), or possibly a bridge(4)")
>>
>> That's simply a matter of observability.
>>
>> It would be a simple matter to use nicctl or drvctl or some
>> other tool to display a mapping between hardware devices and
>> network interface names.
>>
>>> and I also like being
>>> able to classify interfaces looking  at their name,
>>
>> Right, you like being able to see the driver name.
>>
>> See above for observability.
>>
>>> But I also see a need to be able to refer to them using a different name.
>>> But this is different from a rename.
>>
>>> I really think the feature we want is "alias", not "rename".
>>
>> I'm not so sure.
>>
>> A network interface name is an entity in the BSD kernel that
>> has a relationship with a list of addresses. Similarly those
>> addresses have a relationship with a single interface name.
>> That's a very simple model that doesn't allow for any
>> confusion or problems. There is a strict 1 to 1 relationship
>> between address and interface name.
>>
>> Aliases break that.
>>
>> Say I give fxp0 an alias of net0 and I then do
>> "ifconfig net0 1.2.3.4". Now if I do "ifconfig net0" that
>> IP address will show up as assigned to it. But if I do
>> "netstat -nrf inet", net0 is nowhere to be seen. Why?
> 
> You will get an error when doing an ifconfig net0, something like
> ifconfig <keywork>:net0 should be used, to clearly differentiate
> between real interfaces an aliases. So if you use the alias to
> configure it you should be aware that it is an alias (or an
> alternative name, since alias has other meaning in network
> terminology).

If I can't use it with tools like ifconfig then what
is the point of having the alternative name at all?

A name that can be used "some of the time" isn't really
very useful and will create confusion with users.

Darren