Re: [Madwifi-devel] driver questions

[<lo...@cl...>]

Quoting Mathieu Lacage <Mat...@so...>:

> hi all, sam,
> 
> The good news is that I should be able to release a new (at last
> working!) of the BSD port code tomorow. There is no bad news, just a
> question.
fine !
> 
> I would like to know if the following is right:
> 
>   - incoming frame from hardware:  
>       -----------------------
>       | 802.11 | LLC | Data |
>       -----------------------
> 
>   - outgoing frame to network stack (propagation from hardware to
> network stack for reception):
>          --------------------
>          | Eth | LLC | Data |
>          --------------------
> 
>   - incoming frame from network stack:
>             -----------------
>             | Eth    | Data |
>             -----------------
> 

I'm not sure you can't get LLC at this stage... because some frame types have
a different LLC (not 0x00 0x00 0x00 of encapsulated ethernet) that shouldn't be
bothered of in the driver (I mean that it's not the driver's point to add this
LLC that differs from the encapsulated ethernet), since it would require every
driver to check for the "Ethertype" field and adjust depending on the value.
Thus it would require using this "Ethertype" field the wrong way (because
ethertypes are only for encapsulated ethernet hence the name). Cisco comes to
mind... CDP packets are LLC 0x00 0x00 0x0C and protocol 0x20 0x00. So if you
send LLC 0x00 0x00 0x00, and then 0x20 0x00 for protocol, this would be
wrong.... However it won't break the legacy TCP/IP network stack that only uses
encapsulated ethernet (triple 0x00 LLC).

Of course, all this explanation IIRC ;^) But should it make sense, then you
could just add LLC everywhere... IIRC again, frames from TCP/IP stack at least
(either v4 or v6) arrive without LLC.

>   - outgoing frame to hardware (propagation from network stack to
> hardware for emission):
>       -----------------------
>       | 802.11 | LLC | Data |
>       -----------------------
> 
> To the networking stack, the driver behaves just like any random
> ethernet driver. Is this right ?

at least that's the spirit, if not the truth :)

Jean