From mboxrd@z Thu Jan  1 00:00:00 1970
From: "David S. Miller" <davem@redhat.com>
Subject: Re: [PATCH] Handle shared SKBs in VLAN receive code
Date: Mon, 13 Oct 2003 10:19:35 -0700
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To: Tommy Christensen <tommy.christensen@tpack.net>
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On Sun, 12 Oct 2003 12:00:09 +0200
Tommy Christensen <tommy.christensen@tpack.net> wrote:

> Bear with me, but this is how I understand it:
> 
>   - The sk_buff *structure* is read-only on a shared SKB.
>     skb_share_check(skb) breaks the sharing, thus allowing
>     updates of skb->dev, skb->len etc.
>     But the SKB still points at the same data buffer.
> 
>   - The *data* buffer is read-only on a cloned SKB.
>     skb_cow() or skb_copy() or ... gives us a writeable buffer.

skb_copy() makes both the struct sk_buff and the data it points
to unique and yours alone to modify however you wish.