Using Wireless Extensions in a Kernel Module

Using Wireless Extensions in a Kernel Module

[Tim Schneider]

Hi,

I am trying to write a Kernel Module with an implementation of a new  
TCP-Algorithm. Since I need to know the RSSI-Value (Received Signal  
Strength indication) of the sent package, I extended the Pluggable  
Congestion Control Mechanism by a new function which is called right  
after the package is send. At that point, I need to read the RSSI-Value.

I'm now trying to somehow access that value, but I can't figure out  
how. I've come as far, that I found out about the Wirelless  
Extensions, which seem to be very promising. In the header file the  
author states, that this mechanism can be used by both user-space apps  
and kernel modules. Unfortunately nobody seems to ever have used it in  
kernel space, since I can't find any documentations about it.

I would be very glad, if somebody could give me link to a page  
containing informations about this topic, or even just a hint that  
could help me.

Thank you

Tim Schneider

Re: Using Wireless Extensions in a Kernel Module

[Marcel Holtmann]

Hi Tim,

> I am trying to write a Kernel Module with an implementation of a new  
> TCP-Algorithm. Since I need to know the RSSI-Value (Received Signal  
> Strength indication) of the sent package, I extended the Pluggable  
> Congestion Control Mechanism by a new function which is called right  
> after the package is send. At that point, I need to read the RSSI-Value.
> 
> I'm now trying to somehow access that value, but I can't figure out  
> how. I've come as far, that I found out about the Wirelless  
> Extensions, which seem to be very promising. In the header file the  
> author states, that this mechanism can be used by both user-space apps  
> and kernel modules. Unfortunately nobody seems to ever have used it in  
> kernel space, since I can't find any documentations about it.
> 
> I would be very glad, if somebody could give me link to a page  
> containing informations about this topic, or even just a hint that  
> could help me.

we are in the process of killing Wireless Extensions (WEXT) and
replacing it with a netlink based cfg80211/nl80211 interface. The better
mailing list is linux-wireless@vger.kernel.org for such questions.

Regards

Marcel

Re: Using Wireless Extensions in a Kernel Module

[Tim Schneider]

Hi Glen, hi Marcel

thank you for your answers.

I am trying to develop the algorithm for a wireless multihop network,  
so no, I'm not making the classical error ;) Still you're right that I  
should consider the possibility, that the Algorithm is used on a wired  
network. In that case it definitely should not crash the whole system.

Thank you for your hint with the other mailing list. I'm going to try  
my luck there.

Regards

Tim

Am 11.07.2009 um 10:44 schrieb Glen Turner:
>
> Hi Tim,
>
> I'm not sure you aren't making a classic error of optimising the  
> unusual
> case.
>
> The usual situation is that the TCP sender is on the wired network,  
> the
> TCP receiver is on the wireless network. Since the sender determines  
> the
> packet scheduling, determining the received signal strength at the TCP
> receiver isn't much help.
>
> What would be really, really useful is a channel to get this sort of
> information back to the sender in a form in which the feedback is  
> useful
> even after a RTT/2 delay. There are a few explicit congestion  
> notification
> protocols around, and adapting one of those to add the wireless  
> condition
> of intermediate and end hops could be the sort of useful  
> augmentation that
> gives these protocols enough of an advantage of TCP to be worth  
> deploying.
>
> Best wishes, Glen
>
> -- 
> Glen Turner   <http://www.gdt.id.au/~gdt/>

why some packets lost during transmission?

[jon_zhou]

hi

I try to send packets like this:

for (i=0;i<loop;i++)
{
    dev->hard_start_xmit(my_skb,dev);
}

the 'dev' point to network device.

but too many packets lost if the 'loop' is big(i.e. 5000),  I suspect the tx buffer of the NIC is full,but the driver does not print any related info.

how does the upper layer(i.e.arp,qdisc) handle this situation?



Thanks&Regards,
zhou rui

Re: why some packets lost during transmission?

[Jesper Dangaard Brouer]

On Wed, 15 Jul 2009, jon_zhou@agilent.com wrote:

> I try to send packets like this:
>
> for (i=0;i<loop;i++)
> {
>    dev->hard_start_xmit(my_skb,dev);
> }
>
> the 'dev' point to network device.
>
> but too many packets lost if the 'loop' is big(i.e. 5000), I suspect the 
> tx buffer of the NIC is full,but the driver does not print any related 
> info.

Hint, look at the return value... it returns NETDEV_TX_OK if its okay.

> how does the upper layer(i.e.arp,qdisc) handle this situation?


Have you looked at pktgen?

Doc:
   Documentation/networking/pktgen.txt

Code:
   net/core/pktgen.c

Look at function pktgen_xmit() and notice that in the latest kernels 
the dev->hard_start_xmit function pointer has been changed to 
dev->netdev_ops->ndo_start_xmit.


Cheers,
   Jesper Brouer

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