Re: [Xen-devel] Reading network data from netback.c

[Wei Liu <wei.liu2@xxxxxxxxxx>]

On Sat, Feb 04, 2017 at 08:42:33AM +0000, #PATHANGI JANARDHANAN JATINSHRAVAN# 
wrote:
> Hi all, Recently, I’ve been trying to modify netback.c to print
> network data that is going into the VM. For example, I’m doing an SSL
> handshake with the VM as the server, and I send the following
> hexadecimal string from the client to the VM:
> 
> 
> 160302002f0100002b03026161616161616161616161616161616161616161616161616161616161616161000002000501000000
> 
> 
> Now,  to read this ingoing data to the VM from netback.c, I’ve been
> trying to get the sk_buff from the function xenvif_rx_action() and
> extract the TCP header from it using the tcp_hdr(skb) function.
> 

Assuming you're using the latest Linux master branch -- make sure you
extract data after the while loop but before xenvif_rx_copy_flush.

> 
> I then try to get the data from the TCP header using the line:
> (unsigned char *)((unsigned char *)tcph + (tcph->doff * 4))
> 

And maybe use some already existing function to extract data instead of
dereferencing on your own?

I don't think there is much I can help from the driver side. I would
suggest you read other code that handles TCP data to get an idea how to
do that.

Wei.

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