[Click] No network header/Segmentation fault

[Eddie Kohler]

Hi Tushar,

I'll just note that:

 > p->push(sizeof(struct click_ether));

this line is not right.  p->push() returns a new packet pointer which you need 
to use.

p = p->push(sizeof(struct click_ether));

is closer.

Eddie


Tushar Soni wrote:
> Hi,
> 
> Thanks for your reply. I tried both MarkIPHeader and CheckIPHeader, but when I use them it gives me segmentation fault. I think the reinterpret_cast<const click_ip *>(p->data()) is not working for this particular decoded packet.
> 
> But I did try something. In my code after I decode I added the following lines:
> 
> p->push(sizeof(struct click_ether));
> p->set_mac_header(p->data(), 14); //This sets the mac header as well as the network header
> click_ip *iph = p->ip_header(); //Now this works and returns the ip header
> p->set_network_header(20); //This essentially sets the transport header
> click_udp *udph = p->udp_header(); //This also works now
> 
> After doing this when I push the packet, then the IPPrint() element (after stripping 14 bytes that i added) is able to print and there are no segmentation faults. So far so good. I send this packet to the tun. But somehow the packet is being dropped or not processed and it never reaches the application layer. I am thinking the initial reason why this packet does not have any network or transport header maybe causing the kernel to drop it. I checked the checksums of both ip and udp header and they seem to be correct. Would you have any ideas why this is happening???
> 
> Thanks a lot for your help.
> 
> Best Regards,
> 
> Tushar
> 
>  Tºüçhé §übt!é
> 
> 
> 
> ----- Original Message ----
> From: Beyers Cronje <bcronje at gmail.com>
> To: Tushar Soni <omega_marines at yahoo.com>
> Cc: click at pdos.csail.mit.edu
> Sent: Friday, July 4, 2008 5:27:59 PM
> Subject: Re: [Click] No network header/Segmentation fault
> 
> 
> Hi,
>  
> You have to use either MarkIPHeader of CheckIPHeader elements to set the IP header annotations. 
>  
> Beyers
> 
> 
> On Fri, Jul 4, 2008 at 5:06 PM, Tushar Soni <omega_marines at yahoo.com> wrote:
> 
> Hi everyone,
> 
> I have a scenario where coding some packets at the access point and decoding the packets at receiver side using click. Now when i decode the packet and use Print() element, the packet structure and ip header looks ok. But when i use IPPrint it gives me segmentation fault. When i try to get the ip header(Packet::ip_header()) or the udp header(Packet::udp_header()) it returns null (so this is the reason why IPPrint does not work). The commented code should explain better about what i am doing and the problems i am facing. I would be glad if someone could help me figure out what i am doing wrong. Thanks.
> 
> Tushar
> 
> For coding i combine a certain number of packets, from ip header onwards(ip header included). So when i decode i should have a packet from ipheader onwards.
> 
> void
> Decoder::check_uncoded(Packet *p) //p is the coded packet
> {
>    FoundPacketsList found_pkts_list;// this is typedef of type : Vector<Packet *>
>    WritablePacket *wp = p->uniqueify();
>   xor_header *xor_h_cod = (xor_header *)wp->data();//i have created my own header
>    int entries_cod = xor_h_cod->get_entries();
>    int coded_hlen = xor_header::get_header_length(entries_cod);
>    for( int i = 0; i < entries_cod; i++)
>    {
>        //_ddhq is a type if queue and here i am basically checking if the ipid of the unocoded packet
>       //is present in the coded header that i created
>        int location =  _ddhq.is_present(xor_h_cod->get_entry_ipid(i));
>        if( location >= 0 )
>        {
>                //if the id is in the coded header i add it to a list
>            found_pkts_list.push_back(_ddhq.packet(location));
>        }
>    }
>    if(found_pkts_list.size() > 0)
>    {
> 
>        bool decodable = false;
>        //this is the condition for decodability
>        if( entries_cod - found_pkts_list.size() == 1)
>        {
>            decodable = true;
>        }
>        //remove my header
>        wp->pull(coded_hlen);
>        FoundPacketsList::iterator x = found_pkts_list.begin();
>        //here i combine the packets in the list with the coded packet to decode it
>        while( x < found_pkts_list.end())
>        {
>            Packet *p_i = (*x);
>            unsigned char *xored_data = (unsigned char *)wp->data();
>            unsigned char *data = (unsigned char *)(p_i->ip_header());
>            int len = p_i->length();
>            for (int i = 0; i < len; i++) {
>                xored_data[i] ^= data[i];
>            }
>            x++;
>        }
>        if(decodable)
>        {
>            //wp = wp->uniqueify();
>            click_chatter("WOOHOO Packet Decoded");
>            click_chatter("Length: %u", wp->length());
> 
>            click_ip *iph = wp->ip_header();
>            //PROBLEM IS HERE ip_header() returns nothing
>            if(!iph)
>                click_chatter("Shitty packet"); // this is always called because the iph is never created
>            else
>            {
>                click_udp *udph = wp->udp_header();
>                if(!udph)
>                    click_chatter("UDP header not found");
>            }
>                //here i push the packet to the higher layers
>                //i use a tun element for this and when i run it gives: no network header as the error
>            output(1).push(wp);
>        }
> 
>    }
>    else
>    {
>        click_chatter("None of the packets found in uncoded queue.");
>        _codedq.push(0,p);
>    }
> }
> 
> 
> 
> 
>  Tºüçhé §übt!é
> 
> 
> 
> 
> 
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