[RFC,net-next 5/6] net: Add a way to copy skbs without affect cache

[Joe Damato <jdamato@fastly.com>]

Add an skb_copier, skb_nocache_copier, which contains function pointers to
nontemporal copy routines.

Using skb_nocache_copier and do_skb_copy_datagram implement
skb_copy_datagram_from_iter_nocache. This function is intended to be used
by callers which would like to copy data into SKBs using nontemporal
instructions to avoid the CPU cache.

Signed-off-by: Joe Damato <jdamato@fastly.com>
---
 include/linux/skbuff.h |  2 ++
 net/core/datagram.c    | 12 ++++++++++++
 2 files changed, 14 insertions(+)

diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index 97de40b..32c0cba 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -3918,6 +3918,8 @@ int skb_copy_and_hash_datagram_iter(const struct sk_buff *skb, int offset,
 			   struct ahash_request *hash);
 int skb_copy_datagram_from_iter(struct sk_buff *skb, int offset,
 				 struct iov_iter *from, int len);
+int skb_copy_datagram_from_iter_nocache(struct sk_buff *skb, int offset,
+				 struct iov_iter *from, int len);
 int zerocopy_sg_from_iter(struct sk_buff *skb, struct iov_iter *frm);
 void skb_free_datagram(struct sock *sk, struct sk_buff *skb);
 void __skb_free_datagram_locked(struct sock *sk, struct sk_buff *skb, int len);
diff --git a/net/core/datagram.c b/net/core/datagram.c
index a87c41b..da8557b 100644
--- a/net/core/datagram.c
+++ b/net/core/datagram.c
@@ -543,6 +543,11 @@ struct skb_copier skb_copier = {
 	.copy_page_from_iter = copy_page_from_iter
 };
 
+struct skb_copier skb_nocache_copier = {
+	.copy_from_iter = copy_from_iter_nocache,
+	.copy_page_from_iter = copy_page_from_iter_nocache
+};
+
 static int do_skb_copy_datagram(struct sk_buff *skb, int offset,
 				struct iov_iter *from, int len, struct skb_copier copier)
 {
@@ -611,6 +616,13 @@ static int do_skb_copy_datagram(struct sk_buff *skb, int offset,
 	return -EFAULT;
 }
 
+int skb_copy_datagram_from_iter_nocache(struct sk_buff *skb, int offset,
+					struct iov_iter *from, int len)
+{
+	return do_skb_copy_datagram(skb, offset, from, len, skb_nocache_copier);
+}
+EXPORT_SYMBOL(skb_copy_datagram_from_iter_nocache);
+
 /**
  *	skb_copy_datagram_from_iter - Copy a datagram from an iov_iter.
  *	@skb: buffer to copy
-- 
2.7.4