Difference between skb_put() and skb_push()

Difference between skb_put() and skb_push()

[Akshay Kawale]

Hi,

I was wondering about the difference between skb_put() and skb_push().
Both appear to take in the same parameters and produce the same result
- that of lengthening the data area.

If I wanted to add data before the current data area, which one should I use?
(e.g. my data is 5678... and I wanted to prepend 1234 to it).

I am using these functions in a Netfilter hook to insert a header
between TCP and IP for a course project I am doing.

Please help me!!! :-)

Thanks.

- Akshay

Re: Difference between skb_put() and skb_push()

[YOSHIFUJI Hideaki / 吉藤英明]

In article <72252ed05033021463a1f45b6@mail.gmail.com> (at Thu, 31 Mar 2005 00:46:03 -0500), Akshay Kawale <linux781@gmail.com> says:

> I was wondering about the difference between skb_put() and skb_push().
> Both appear to take in the same parameters and produce the same result
> - that of lengthening the data area.
> 
> If I wanted to add data before the current data area, which one should I use?
> (e.g. my data is 5678... and I wanted to prepend 1234 to it).

http://www.skbuff.net/skbbasic.html

--yoshfuji

Re: Difference between skb_put() and skb_push()

[Akshay Kawale]

Hi,

I am trying to access the tot_len field in the IP Header using a
sk_buff structure inside a Netfilter hook.

I do something like:

(**skb).nh.iph->tot_len += 64

I have tried other variants of the same statement but none of them work.
I want to increment the length by 64 bytes, but it gives me an error
saying that I am trying to access an 'incomplete data type'.

Can anyone shed some light on this problem?
tot_len if of type __u16 (unsigned short int).

Thanks.

- Akshay