Just a question.
I'm studying TCP-IP stack in kernel 2.4 and I'm not able to understand
the difference between fields len and data_len in struct skb_buff.
Infact if we see typical steps in sending we could see
/* Only tailroom */
skb = alloc_skb(headerlen + len, GFP_KERNEL);
/* Reserve space for header */
skb_reserve(skb, headerlen);
/* Reserve space for data */
skb_put(skb, len);
[..]
Now skb_put appears as follows.
static inline unsigned char *skb_put(struct sk_buff *skb, unsigned int len)
{
unsigned char *tmp=skb->tail;
SKB_LINEAR_ASSERT(skb);
skb->tail+=len;
skb->len+=len;
if(skb->tail>skb->end) {
skb_over_panic(skb, len, current_text_addr());
}
return tmp;
}
I can see it updates only skb->len.
So I thought that difference could be
- skb->len is the number of bytes reserved for data;
- skb->data_len is the number of bytes actually used in data area
reserved in the buffer obtained through alloc_skb (and so
skb->data_len <= skb->len always).
Is this correct?
Regards,
Angelo Dell'Aera 'buffer'
<buffer@users.sourceforge.net>
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