attach additional value to skb

attach additional value to skb

[Yakov Lerner]

1. How can I attach my 32-bit value to the skb in the
PRE_ROUTNIG hook such that FORWARD and POST_ROUTING
hooks can later access this value from the skb ?

Can I use sk_buff->cb for that ?

2.
I want to add my custom destructor to the skb, the function
pointer to be called at skb destruction time. Will the following
work:  if I push  address of my_destructor to the
sk-buff->destructor field,  and then when my_destructor
is called, I call the (saved)  old value of  sk-buff->destructor ?
Will this work ?

Yakov

Re: attach additional value to skb

[Wenhua Zhao]

On 10/22/07, Yakov Lerner <iler.ml@gmail.com> wrote:
> 1. How can I attach my 32-bit value to the skb in the
> PRE_ROUTNIG hook such that FORWARD and POST_ROUTING
> hooks can later access this value from the skb ?
>
> Can I use sk_buff->cb for that ?
In IP layer cb is used by IP as structure inet_skb_param.  It is
written by ip_rcv_options() (in function ip_rcv_finish()) between
PRE_ROUTING and FORWARD/POST_ROUTING.

In my opinion, cb is only used when one exclusively owns the skb.

Regards,
Wenhua

Re: attach additional value to skb

[Muli Ben-Yehuda]

On Mon, Oct 22, 2007 at 10:03:47PM +0200, Yakov Lerner wrote:

> I want to add my custom destructor to the skb, the function pointer
> to be called at skb destruction time. Will the following work: if I
> push address of my_destructor to the
> sk-buff->destructor field,  and then when my_destructor
> is called, I call the (saved)  old value of  sk-buff->destructor ?
> Will this work ?

It might, provided nothing else runs after you that will unilaterally
change the ->destructor field. I.e., it depends at which point in the
skb's life-time you set your hook.

Cheers,
Muli
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