Linux Kernel Network Programming – struct sk_buff data-structure – skb_clone() skb_copy() APIs

Refer:
skb_clone() – duplicate an sk_buff ↗
skb_copy() – create private copy of an sk_buff ↗

Here is the copy paste of skb_clone() and skb_copy() APIs (/net/core/skbuff.c) from the Kernel-source version 6.5.9 for quick reference:

/**
 *	skb_clone	-	duplicate an sk_buff
 *	@skb: buffer to clone
 *	@gfp_mask: allocation priority
 *
 *	Duplicate an &sk_buff. The new one is not owned by a socket. Both
 *	copies share the same packet data but not structure. The new
 *	buffer has a reference count of 1. If the allocation fails the
 *	function returns %NULL otherwise the new buffer is returned.
 *
 *	If this function is called from an interrupt gfp_mask() must be
 *	%GFP_ATOMIC.
 */

struct sk_buff *skb_clone(struct sk_buff *skb, gfp_t gfp_mask)
{
	struct sk_buff_fclones *fclones = container_of(skb,
						       struct sk_buff_fclones,
						       skb1);
	struct sk_buff *n;

	if (skb_orphan_frags(skb, gfp_mask))
		return NULL;

	if (skb->fclone == SKB_FCLONE_ORIG &&
	    refcount_read(&fclones->fclone_ref) == 1) {
		n = &fclones->skb2;
		refcount_set(&fclones->fclone_ref, 2);
		n->fclone = SKB_FCLONE_CLONE;
	} else {
		if (skb_pfmemalloc(skb))
			gfp_mask |= __GFP_MEMALLOC;

		n = kmem_cache_alloc(skbuff_cache, gfp_mask);
		if (!n)
			return NULL;

		n->fclone = SKB_FCLONE_UNAVAILABLE;
	}

	return __skb_clone(n, skb);
}
EXPORT_SYMBOL(skb_clone);

/**
 *	skb_copy	-	create private copy of an sk_buff
 *	@skb: buffer to copy
 *	@gfp_mask: allocation priority
 *
 *	Make a copy of both an &sk_buff and its data. This is used when the
 *	caller wishes to modify the data and needs a private copy of the
 *	data to alter. Returns %NULL on failure or the pointer to the buffer
 *	on success. The returned buffer has a reference count of 1.
 *
 *	As by-product this function converts non-linear &sk_buff to linear
 *	one, so that &sk_buff becomes completely private and caller is allowed
 *	to modify all the data of returned buffer. This means that this
 *	function is not recommended for use in circumstances when only
 *	header is going to be modified. Use pskb_copy() instead.
 */

struct sk_buff *skb_copy(const struct sk_buff *skb, gfp_t gfp_mask)
{
	int headerlen = skb_headroom(skb);
	unsigned int size = skb_end_offset(skb) + skb->data_len;
	struct sk_buff *n = __alloc_skb(size, gfp_mask,
					skb_alloc_rx_flag(skb), NUMA_NO_NODE);

	if (!n)
		return NULL;

	/* Set the data pointer */
	skb_reserve(n, headerlen);
	/* Set the tail pointer and length */
	skb_put(n, skb->len);

	BUG_ON(skb_copy_bits(skb, -headerlen, n->head, headerlen + skb->len));

	skb_copy_header(n, skb);
	return n;
}
EXPORT_SYMBOL(skb_copy);