Porting the RTSP module to 2.6.22

Porting the RTSP module to 2.6.22

[Michael Guntsche]

Hello,

I am trying to forward port the RTSP module from 2.6.21 to 2.6.22 and  
I am nearly done. All there is missing is a helper function. I had a  
look at the skbuff struct but I could not find out what needed to be  
changed.

Here is the short original helper function.

static void
get_skb_tcpdata(struct sk_buff* skb, char** pptcpdata, uint*  
ptcpdatalen)
{
     struct iphdr*   iph  = (struct iphdr*)skb->nh.iph;
     struct tcphdr*  tcph = (struct tcphdr*)((char*)iph + iph->ihl*4);

     *pptcpdata = (char*)tcph + tcph->doff*4;
     *ptcpdatalen = ((char*)skb->h.raw + skb->len) - *pptcpdata;
}

I changed this to

static void
get_skb_tcpdata(struct sk_buff** skb, char** pptcpdata, uint*  
ptcpdatalen)
{
     struct iphdr*   iph  = ip_hdr(*skb);
     struct tcphdr*  tcph = (void *)iph + iph->ihl*4;

     *pptcpdata = (char*)tcph + tcph->doff*4;
     *ptcpdatalen = ((char*)skb->h.raw + skb->len) - *pptcpdata;
}

I am pretty sure, that the first three lines are ok. But the last one  
is giving me some problems, since "h" is no longer in the skb struct.
Maybe someone with a little bit more knowledge about the changes can  
help me here.

Kind regards,
Michael

Re: Porting the RTSP module to 2.6.22

[Jan Engelhardt]

On Jul 29 2007 22:12, Michael Guntsche wrote:
>
> I changed this to
>
> static void
> get_skb_tcpdata(struct sk_buff** skb, char** pptcpdata, uint* ptcpdatalen)
> {
>   struct iphdr*   iph  = ip_hdr(*skb);
>   struct tcphdr*  tcph = (void *)iph + iph->ihl*4;

Use  (void *)iph + ip_hdrlen(*skb)

>   *pptcpdata = (char*)tcph + tcph->doff*4;
>   *ptcpdatalen = ((char*)skb->h.raw + skb->len) - *pptcpdata;
> }

h.raw is now skb_transport_header(skb);
Also, skb-> should be (*skb)->, since it is a double pointer (which you
can also get rid of)

> I am pretty sure, that the first three lines are ok. But the last one is giving
> me some problems, since "h" is no longer in the skb struct.
> Maybe someone with a little bit more knowledge about the changes can help me
> here.


	Jan
-- 

Re: Porting the RTSP module to 2.6.22

[Michael Guntsche]

On Jul 29, 2007, at 22:21, Jan Engelhardt wrote:

>
>
> Use  (void *)iph + ip_hdrlen(*skb)
>
>>   *pptcpdata = (char*)tcph + tcph->doff*4;
>>   *ptcpdatalen = ((char*)skb->h.raw + skb->len) - *pptcpdata;
>> }
>
> h.raw is now skb_transport_header(skb);
> Also, skb-> should be (*skb)->, since it is a double pointer (which  
> you
> can also get rid of)
>

Thank you very very much Jan. With your tips  and some poking in the  
other modules I was able to get a compiling and more suprisingly  
running version of the RTSP module.

The new and working function looks like this.

static void
get_skb_tcpdata(struct sk_buff* skb, char** pptcpdata, uint*  
ptcpdatalen)
{
     struct iphdr*   iph  = ip_hdr(skb);
     struct tcphdr*  tcph = (void *)iph + ip_hdrlen(skb);

     *pptcpdata = (char*)tcph +  tcph->doff*4;
     *ptcpdatalen = ((char*)skb_transport_header(skb) + skb->len) -  
*pptcpdata;
}


I am in the process of creating and updated patch against 2.6.22.1  
and will put it up on my site this evening.
http://mike.it-loops.com/rtsp/
It is working for me right now, but maybe someone can give it a quick  
check and tell me if there are any problems or bugs.

Kind regards,
Michael

Re: Porting the RTSP module to 2.6.22

[Michael Guntsche]

Answering my own post.
I already fixed the obvious mistake I made.
On Jul 29, 2007, at 22:12, Michael Guntsche wrote:
<snip>
> I changed this to
>
> static void
> get_skb_tcpdata(struct sk_buff** skb, char** pptcpdata, uint*  
> ptcpdatalen)
> {
>     struct iphdr*   iph  = ip_hdr(*skb);
>     struct tcphdr*  tcph = (void *)iph + iph->ihl*4;
>
>     *pptcpdata = (char*)tcph + tcph->doff*4;
>     *ptcpdatalen = ((char*)skb->h.raw + skb->len) - *pptcpdata;
> }
>

Of course there is no need to change skb.
Sorry for not checking this before sending the first E-Mail.

static void
get_skb_tcpdata(struct sk_buff* skb, char** pptcpdata, uint*  
ptcpdatalen)
{
     struct iphdr*   iph  = ip_hdr(skb);
     struct tcphdr*  tcph = (void *)iph + iph->ihl*4;

     *pptcpdata = (char*)tcph + tcph->doff*4;
     *ptcpdatalen = ((char*)skb->h.raw + skb->len) - *pptcpdata;
}

The problem remains though that the "h" member is no longer existing.


Kind regards,
Michael

Re: Porting the RTSP module to 2.6.22

[Patrick McHardy]

Michael Guntsche wrote:
> Answering my own post.
> I already fixed the obvious mistake I made.
> On Jul 29, 2007, at 22:12, Michael Guntsche wrote:
> <snip>
> 
>> I changed this to
>>
>> static void
>> get_skb_tcpdata(struct sk_buff** skb, char** pptcpdata, uint* 
>> ptcpdatalen)
>> {
>>     struct iphdr*   iph  = ip_hdr(*skb);
>>     struct tcphdr*  tcph = (void *)iph + iph->ihl*4;
>>
>>     *pptcpdata = (char*)tcph + tcph->doff*4;
>>     *ptcpdatalen = ((char*)skb->h.raw + skb->len) - *pptcpdata;
>> }
>>
> 
> Of course there is no need to change skb.
> Sorry for not checking this before sending the first E-Mail.
> 
> static void
> get_skb_tcpdata(struct sk_buff* skb, char** pptcpdata, uint*  ptcpdatalen)
> {
>     struct iphdr*   iph  = ip_hdr(skb);
>     struct tcphdr*  tcph = (void *)iph + iph->ihl*4;
> 
>     *pptcpdata = (char*)tcph + tcph->doff*4;
>     *ptcpdatalen = ((char*)skb->h.raw + skb->len) - *pptcpdata;
> }
> 
> The problem remains though that the "h" member is no longer existing.


That shouldn't be a problem since netfilter modules should basically
never use it anyway since its only valid for locally generated packets.
Use Jan's suggestion (or look at other modules) and skb_header_pointer.