net: introduce skb_try_coalesce()

Move tcp_try_coalesce() protocol independent part to
skb_try_coalesce().

skb_try_coalesce() can be used in IPv4 defrag and IPv6 reassembly,
to build optimized skbs (less sk_buff, and possibly less 'headers')

skb_try_coalesce() is zero copy, unless the copy can fit in destination
header (its a rare case)

kfree_skb_partial() is also moved to net/core/skbuff.c and exported,
because IPv6 will need it in patch (ipv6: use skb coalescing in
reassembly).

Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Alexander Duyck <alexander.h.duyck@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 86 insertions, 0 deletions

diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index 7ceb673d622f..016694d62484 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -3346,3 +3346,89 @@ void __skb_warn_lro_forwarding(const struct sk_buff *skb)
 			     skb->dev->name);
 }
 EXPORT_SYMBOL(__skb_warn_lro_forwarding);
+
+void kfree_skb_partial(struct sk_buff *skb, bool head_stolen)
+{
+	if (head_stolen)
+		kmem_cache_free(skbuff_head_cache, skb);
+	else
+		__kfree_skb(skb);
+}
+EXPORT_SYMBOL(kfree_skb_partial);
+
+/**
+ * skb_try_coalesce - try to merge skb to prior one
+ * @to: prior buffer
+ * @from: buffer to add
+ * @fragstolen: pointer to boolean
+ *
+ */
+bool skb_try_coalesce(struct sk_buff *to, struct sk_buff *from,
+		      bool *fragstolen, int *delta_truesize)
+{
+	int i, delta, len = from->len;
+
+	*fragstolen = false;
+
+	if (skb_cloned(to))
+		return false;
+
+	if (len <= skb_tailroom(to)) {
+		BUG_ON(skb_copy_bits(from, 0, skb_put(to, len), len));
+		*delta_truesize = 0;
+		return true;
+	}
+
+	if (skb_has_frag_list(to) || skb_has_frag_list(from))
+		return false;
+
+	if (skb_headlen(from) != 0) {
+		struct page *page;
+		unsigned int offset;
+
+		if (skb_shinfo(to)->nr_frags +
+		    skb_shinfo(from)->nr_frags >= MAX_SKB_FRAGS)
+			return false;
+
+		if (skb_head_is_locked(from))
+			return false;
+
+		delta = from->truesize - SKB_DATA_ALIGN(sizeof(struct sk_buff));
+
+		page = virt_to_head_page(from->head);
+		offset = from->data - (unsigned char *)page_address(page);
+
+		skb_fill_page_desc(to, skb_shinfo(to)->nr_frags,
+				   page, offset, skb_headlen(from));
+		*fragstolen = true;
+	} else {
+		if (skb_shinfo(to)->nr_frags +
+		    skb_shinfo(from)->nr_frags > MAX_SKB_FRAGS)
+			return false;
+
+		delta = from->truesize -
+			SKB_TRUESIZE(skb_end_pointer(from) - from->head);
+	}
+
+	WARN_ON_ONCE(delta < len);
+
+	memcpy(skb_shinfo(to)->frags + skb_shinfo(to)->nr_frags,
+	       skb_shinfo(from)->frags,
+	       skb_shinfo(from)->nr_frags * sizeof(skb_frag_t));
+	skb_shinfo(to)->nr_frags += skb_shinfo(from)->nr_frags;
+
+	if (!skb_cloned(from))
+		skb_shinfo(from)->nr_frags = 0;
+
+	/* if the skb is cloned this does nothing since we set nr_frags to 0 */
+	for (i = 0; i < skb_shinfo(from)->nr_frags; i++)
+		skb_frag_ref(from, i);
+
+	to->truesize += delta;
+	to->len += len;
+	to->data_len += len;
+
+	*delta_truesize = delta;
+	return true;
+}
+EXPORT_SYMBOL(skb_try_coalesce);