RE: IPv6 - why skb->cb is not filled???

From: Hen, Shmulik (shmulik.hen@intel.com)
Date: Thu Aug 14 2003 - 04:54:16 EST


> -----Original Message-----
> From: Adam Flizikowski [mailto:adam_fli@xxxxxxxxxxxxxx]
> Sent: Thursday, August 14, 2003 12:23 PM
> To: linux-net@xxxxxxxxxxxxxxx
> Subject: IPv6 - why skb->cb is not filled???
> Importance: High
>
>
> Hello,
>
> I have added packet numbering at driver level (8139too.c):
> - after data is taken from eth and skb reserved i put a number
> sprintf(skb->cb,"%lu",pkt_nr) which is ++'ed every pkt
>
> later on, in ip6_input.c i try to read skb->cb and ... it is
> empty (or has
> not proper value).
>
> Whereas when i try to read skb->cb from ip_input.c (ipv4) it
> is properly
> read.
>
> Could you please advice me what can be wrong?
>
> Does ipv6 uses header file other than skbuff.h ??? .. and
> thus different skb
> struct???
>
>
> best regards
>
> adam
>

skb->cb is only guaranteed to contain valid values between one
layer and the one directly below or above it. It is *not*
guaranteed to have the same value when passing onward. Meaning
TCP can put info for IP, and IP is allowed to overwrite with it's
own info before passing to the device.

--
| Shmulik Hen Advanced Network Services |
| Israel Design Center, Jerusalem |
| LAN Access Division, Platform Networking |
| Intel Communications Group, Intel corp. |

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