[Ns-developers] virtual netdevice (Was: release update [feedback needed])

[Gustavo Carneiro]

(changing subject or else a lot of disparate topics are mixed into the same
thread!)

2009/6/10 Tom Henderson <tomh at tomh.org>
[...]

>
>>
>>
>>    Gustavo,
>>    - I thought you were going to clean up the Receive/PromiscReceive
>>    separate functions?
>>
>>
>> I don't understand the concern here, or what I should do.  If I remove one
>> of them, which one do I keep?  How can we be sure it's the right one?
>>
>>  - Receive() is simpler to use and usually what we want, but does not
>> support simulating frames received by a bridge;
>>
>>  - PromiscReceive takes more parameters, harder to use if you  want to do
>> something simpler, but needed for certain scenarios.
>>
>
> My comment was that all of the other net devices call the promisc callback
> out of Receive(), but here, the user has to pick PromiscReceive or Receive()
> and I'm not sure how he or she picks the right one.
>
> Can you describe the use case for PromiscReceive?  You implied bridging but
> I'm not seeing it.


I cannot possibly know all the use cases of VirtualNetDevice.  However, not
supporting PromiscReceive will mean that not all functionality of NetDevice
is made available by VirtualNetDevice.  Indeed, one use case is a "virtual
bridge port", i.e. a bridge port that is not physical but instead is, for
example, a TCP link.  Why this scenario or others matter is not my job to
point out, I just don't want to limit functionality if the cost of
supporting the funcionality is low.  You seem to think the cost is high
because having PromisReceive will confuse users.  I think the whole
VirtualNetDevice is already for advanced users who know what they are
doing.  That's one of the reasons why VirtualNetDevice does not have a
"helper class".  The whole point is that subclassing NetDevice is _a lot_ of
work, work that is not justified for certain kinds of scenarios, and
VirtualNetDevice avoids subclassing.

-- 
Gustavo J. A. M. Carneiro
INESC Porto, Telecommunications and Multimedia Unit
"The universe is always one step beyond logic." -- Frank Herbert