Re: Skb and ieee80211 headers

["Arend van Spriel" <arend@broadcom.com>]

On 07/31/2013 02:39 PM, Mathieu Devos wrote:
> Hi,
>
> The wireless chip is a Broadcast BCM4330 chip. After looking around a
> bit I found that this is a fullMAC and links to the driver on
> wireless.kernel: http://wireless.kernel.org/en/users/Drivers/brcm80211
> and also links directly to android itself:
> https://android.googlesource.com/platform/hardware/broadcom/wlan

I suspected. The bcm4330 is indeed a fullmac device, which means the 
802.11 stack is running on the device. The driver on Android is located 
under:

https://android.googlesource.com/kernel/samsung/+/android-samsung-3.0-ics-mr1/drivers/net/wireless/bcmdhd/

Not sure which android version you have.

The brcm80211 on wireless.kernel.org is the upstream linux driver.

Gr. AvS

> Still trying to learn a lot in this tightly packed world of protocol
> stacks, wireless and all the other poisons. Seems like I still have a
> long way to go. Thank you already for helping me out with these issues
> and taking the time to explain these things to me.
>
> Kind regards,
> Mathieu Devos
>
> On Wed, Jul 31, 2013 at 1:05 PM, Arend van Spriel <arend@broadcom.com> wrote:
>> On 07/31/2013 12:28 PM, Mathieu Devos wrote:
>>>
>>> Hi,
>>>
>>> It's an android smartphone (I 9100 - Samsung galaxy S2) so it does not
>>> have a normal ethernet 802.3 input even. I check before selecting the
>>> device that it's wireless (through ieee80211_ptr) and this properly
>>> returns the wlan0 device which should be on the 80211 standard.
>>
>>
>> *sigh* Welcome in the world of protocol stacks, wireless, networking (choose
>> your poison). Let me draw the picture.
>>
>>          o user-space
>>          |
>> ----------------------
>>          | kernel
>>    +-----------+
>>    |    NET    | networking subsystem, ie. TCP/IP stack
>>    +-----------+
>>          | 802.3
>> +----------------+
>> |       | driver |
>> | +------------+ |
>> | |802.11 stack| |
>> | +------------+ |
>> |       | 802.11 |
>> +----------------+
>>          |
>>          o RF
>>
>> The device hooks up to the networking subsystem as an ethernet device and as
>> such it receives 802.3 packets. These are converted to 802.11 packets by the
>> 802.11 stack. Now depending on your device that happens in the device driver
>> or on the device itself. Another option is that this is done by mac80211
>> (kernel provided 802.11 stack), but that is probably not the case, but to be
>> sure I ask again: what wireless device do you have in your galaxy S2?
>>
>> Gr. AvS
>>
>>
>>> My goal is to get the ieee80211_header properly on the skb with this
>>> device, but some of the pointers and original data in the skb seem
>>> totally off. This leaves me clueless as to where to put this
>>> ieee80211_header.
>>> I've tried putting it right on skb->head (wrong I know, but I was
>>> getting desperate), on skb->mac_header (also wrong, no idea why
>>> though), I went back from skb->tail with len and even added ETH_HLEN
>>> to that as well because you can see that before my hook gets
>>> activated: skb_pull_inline(skb, ETH_HLEN);
>>> In the end I'm left with a header that is forced onto data but with a
>>> wrong origin pointer thus basically leaving me with all wrong data in
>>> the header.
>>>
>>> Kind regards,
>>> Mathieu Devos
>>>
>>> On Wed, Jul 31, 2013 at 12:08 PM, Arend van Spriel <arend@broadcom.com>
>>> wrote:
>>>>
>>>> On 07/31/2013 11:39 AM, Mathieu Devos wrote:
>>>>>
>>>>>
>>>>> Hi,
>>>>>
>>>>> I hope this is the right place to ask for a little bit of help as I'm
>>>>> currently beyond stuck on a challenge I'm trying to accomplish. I'm
>>>>> trying to write a "simple" LKM that properly uses a ieee80211 header
>>>>> to print information about the mac addresses (addr1->addr4) and later
>>>>> down the road try to send my own data.
>>>>>
>>>>> I only need to get L2 working, no need for TCP/IP, just a proper
>>>>> ieee80211 based on input from skb would be huge for me.
>>>>>
>>>>> So my issue: when placing the ieee80211 on my mac_header after I hook
>>>>> my skb from my wireless device (wlan0 on android - I9100)
>>>>
>>>>
>>>>
>>>> Not sure what you goal is, but what wireless device is that? You may just
>>>> get 802.3 packets from the device.
>>>>
>>>> Gr. AvS
>>>>
>>>>
>>>>> I get a huge
>>>>> amount of zero's and random(?) numbers when trying to print the
>>>>> addresses. This leads me to the first conclusion that mac_header is
>>>>> placed wrong when using 80211. After that I saw a lot of people just
>>>>> using the skb->data pointer. Now this gives even weirder issues for me
>>>>> and actually totally crashes my kernel.
>>>>
>>>>
>>>>
>>>>
>>>>
>>>
>>
>>
>