On Thu, Sep 18, 2014 at 06:03:36PM +0100, Simon Vincent wrote: > > On 18/09/14 17:30, Alexander Aring wrote: > >On Thu, Sep 18, 2014 at 04:54:53PM +0100, Simon Vincent wrote: > >>It looks like in 6lowpan_iphc.c lowpan_header_compress the original ipv6 > >>header is removed and the compressed header is attached. > >> > >>These four lines are responsible. > >> skb_pull(skb, sizeof(struct ipv6hdr)); > >> skb_reset_transport_header(skb); > >> memcpy(skb_push(skb, hc06_ptr - head), head, hc06_ptr - head); > >> skb_reset_network_header(skb); > >> > >>I don't think we can do this as the skb is being used in other parts of the > >>ip stack. Hence when the ipv6 header is read elsewhere the addresses become > >>corrupt as they have been overwritten by the 6lowpan compressed header. > >> > >>Any ideas on how to fix this? > >> > >yes, but I don't believe that this makes trouble. <--- or only makes > >trouble by replacing data, see below. > > > >It's called by a callback of header_ops [0]. > > > >This is for generating the mac header with address information from > >neighbor discovery cache (mainly destination address) and source > >addresse (mainly netdev->dev_addr). > > > >Another example of this function is ethernet. [1] > > > >On [1] you will se that the ethernet header will created there. > > > >- Get data from skb for ethhdr (ethernet header) > > struct ethhdr *eth = (struct ethhdr *)skb_push(skb, ETH_HLEN); > > > >- memcpy(eth->h_source, saddr, ETH_ALEN); <-- source address > > > >- memcpy(eth->h_dest, daddr, ETH_ALEN); <-- destination address. > > > > > >So they using the callback there to manipulate the skb here. > > > >Another idea is that, maybe we can ADD data but not REPLACING existing > >data with that. I don't know right now. > I think what is done in ethernet is fine as they are adding data. But in the > lowpan_header_compress we are doing a skb_pull to remove the existing ipv6 > header before adding on the new 6lowpan header, so we are replacing the > existing data. Yep, then you could try to test what I did there. Simple save the address information in reserved skb data and then replacing data in lowpan_xmit callback. This also solves the capture on lowpan interfaces. lowpan_xmit should be save to replacing the header. - Alex -- To unsubscribe from this list: send the line "unsubscribe linux-wpan" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
