- struct sk_buff * build_skb(void * data, unsigned int frag_size);
- data buffer provided by caller
- size of fragment, or 0 if head was kmalloced
Allocate a new sk_buff. Caller provides space holding head and skb_shared_info. data must have been allocated by kmalloc only if frag_size is 0, otherwise data should come from the page allocator. The return is the new skb buffer. On a failure the return is NULL, and data is not freed.
Before IO, driver allocates only data buffer where NIC put incoming frame Driver should add room at head (NET_SKB_PAD) and MUST add room at tail (SKB_DATA_ALIGN(skb_shared_info)) After IO, driver calls build_skb, to allocate sk_buff and populate it before giving packet to stack. RX rings only contains data buffers, not full skbs.