Sending Ethernet packets using dev_queue_xmit from device driver module

[Girish Bopaiah]

Dear All,

I have to send some Ethernet packets from my device driver module.

Have completely created Ethernet packet(including mac, IP and data)

By googling I got some API's like dev_queue_xmit.

Could you please guide me on this with example if you have any

--

Regards,
Girish

[Anil Kumar Pugalia]

Check on of the usage examples in the files listed at http://lxr.free-electrons.com/ident?i=dev_queue_xmit

Regards
Anil

Passion: http://sysplay.in (Playing with Systems)

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[Girish Bopaiah]

Thank you very much Anil for the info. I was able send the Ethernet packets

Have few questions, please clarify

• when we do "skb = dev_alloc_skb()",  does the memory allocation happens at  tcp/ip stack?
• If I  call the API  "dev_queue_xmit"  does it communicate with   tcp/ip stack first and then network driver  or directly network driver

• In the standard Ethernet driver the transmit function is igb_xmit_frame(). When I call  "dev_queue_xmit" API , does this call  igb_xmit_frame() of Ethernet driver 
  

Regards,

Girish

On Wed, Aug 3, 2016 at 7:46 PM, Anil Kumar Pugalia <em...@sarika-pugs.com> wrote:

Check on of the usage examples in the files listed at http://lxr.free-electrons.com/ident?i=dev_queue_xmit

Regards
Anil

Passion: http://sysplay.in (Playing with Systems)

Girish Bopaiah wrote on Wednesday 03 August 2016 01:21 PM:

Dear All,

I have to send some Ethernet packets from my device driver module.

Have completely created Ethernet packet(including mac, IP and data)

By googling I got some API's like dev_queue_xmit.

Could you please guide me on this with example if you have any

--

Regards,
Girish

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Regards,
Girish

[Anil Kumar Pugalia]

How does it matter whether at tcp/ip stack or not, because finally it is memory from kernel space?

skb related management is provided the stack layer so what ever skb operations needs to done to transmit the pkt through driver would go through the skb APIs provided by the stack.

Not sure about what is this igb_xmit_frame. Typically the transmit function ptr in the driver is start_xmit.

Regards
Anil

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[Girish Bopaiah]

Thanks Anil.

whatever I mentioned "igb_xmit_frame" is   .ndo_start_xmit

static const struct net_device_ops igb_netdev_ops = {

.ndo_start_xmit     = igb_xmit_frame,

}

The question was does" start_xmit" gets called when I call API "dev_queue_xmit" from other driver module?

[Anil Kumar Pugalia]

Highly likely - may be you have to dig into the code further.

Regards
Anil

Passion: http://sysplay.in (Playing with Systems)

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[Girish Bopaiah]

Yes "igb_xmit_frame" is called. I started debugging code with prints and was able to get prints  for my network packet

I am referring your network training  code also. Its helping me a lot.

Finding out different ways to send packets. Want to use the fastest method since I have to send all the packets after the power failure of system. The hold is very less (9 ms after power failure).

Please let me know if any other alternative to send network packet apart from "dev_queue_xmit" API.  Will try all other probabilities

I  have one more question,  in system  there are many interfaces (eth0,  eth1,  eth2,  eth3). May i Know who assigns this number? Is the network module creating this interface ? which part of the code?

Regards,

Girish

[Anil Kumar Pugalia]

Seeing your exploration spree, I think that you may find many more ways than what I know.

The name assignment is done when we register using register_netdev based on the value filled in net_device structure by APIs like alloc_etherdev, ...

Regards
Anil

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[Girish Bopaiah]

Thanks a lot for info.