Re: Question about ip_rcv() function

[rahul b jain cs student <rbj2@oak.njit.edu>]

Thanks for your response.

I just want to know if my understanding of how the sk_buff structure is
correct.

When data arrives at the TCP layer it is pointed to by the data pointer
and the TCP header goes in the skb->data-skb->head area. When this packet
is passed to the IP layer, skb->tail-skb->data section will now contain
the TCP header + TCP data and now the IP header will be put in the new
skb->data-skb->head area.

Please let me know if this understanding is correct.

I also wanted to know does psk_may_pull() only check for correct header
length or does it (thought some func calls) strip off the IP header ?

Thanks,
Rahul.

On Wed, 23 Jun 2004, David S. Miller wrote:

> On Wed, 23 Jun 2004 14:45:47 -0400 (EDT)
> rahul b jain cs student <rbj2@oak.njit.edu> wrote:
>
> > can anyone explain what is the difference between the following two pieces
> > of code.
> >
> > 1. if (!pskb_may_pull(skb, sizeof(struct iphdr)))
> >                 goto inhdr_error;
> >
> >    iph = skb->nh.iph;
> >
> > 2. if (!pskb_may_pull(skb, iph->ihl*4))
> >                 goto inhdr_error;
> >
> >    iph = skb->nh.iph;
>
> We can't dereference any of the iphdr fields (such as iph->ihl) until
> we know that at least "sizeof(struct iphdr)" bytes are there first.
>