linux-kernel - [RFC,net-next 4/6] net: Add a struct for managing copy functions

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Date:   Tue, 10 May 2022 20:54:25 -0700
From:   Joe Damato <jdamato@...tly.com>
To:     netdev@...r.kernel.org, davem@...emloft.net, kuba@...nel.org,
        linux-kernel@...r.kernel.org, x86@...nel.org,
        Eric Dumazet <edumazet@...gle.com>,
        Paolo Abeni <pabeni@...hat.com>
Cc:     Joe Damato <jdamato@...tly.com>
Subject: [RFC,net-next 4/6] net: Add a struct for managing copy functions

Add struct skb_copier which encapsulates two functions for copying data,
and provide a default copier, skb_copier.

Separate skb_copy_datagram_from_iter into a a helper function,
do_skb_copy_datagram, which takes a struct skb_copier.

Signed-off-by: Joe Damato <jdamato@...tly.com>
---
 net/core/datagram.c | 49 ++++++++++++++++++++++++++++++++-----------------
 1 file changed, 32 insertions(+), 17 deletions(-)

diff --git a/net/core/datagram.c b/net/core/datagram.c
index 50f4fae..a87c41b 100644
--- a/net/core/datagram.c
+++ b/net/core/datagram.c
@@ -532,18 +532,19 @@ int skb_copy_datagram_iter(const struct sk_buff *skb, int offset,
 }
 EXPORT_SYMBOL(skb_copy_datagram_iter);
 
-/**
- *	skb_copy_datagram_from_iter - Copy a datagram from an iov_iter.
- *	@skb: buffer to copy
- *	@offset: offset in the buffer to start copying to
- *	@from: the copy source
- *	@len: amount of data to copy to buffer from iovec
- *
- *	Returns 0 or -EFAULT.
- */
-int skb_copy_datagram_from_iter(struct sk_buff *skb, int offset,
-				 struct iov_iter *from,
-				 int len)
+struct skb_copier {
+	size_t (*copy_from_iter)(void *addr, size_t bytes, struct iov_iter *i);
+	size_t (*copy_page_from_iter)(struct page *page, size_t offset, size_t bytes,
+				      struct iov_iter *i);
+};
+
+struct skb_copier skb_copier = {
+	.copy_from_iter = copy_from_iter,
+	.copy_page_from_iter = copy_page_from_iter
+};
+
+static int do_skb_copy_datagram(struct sk_buff *skb, int offset,
+				struct iov_iter *from, int len, struct skb_copier copier)
 {
 	int start = skb_headlen(skb);
 	int i, copy = start - offset;
@@ -553,7 +554,7 @@ int skb_copy_datagram_from_iter(struct sk_buff *skb, int offset,
 	if (copy > 0) {
 		if (copy > len)
 			copy = len;
-		if (copy_from_iter(skb->data + offset, copy, from) != copy)
+		if (copier.copy_from_iter(skb->data + offset, copy, from) != copy)
 			goto fault;
 		if ((len -= copy) == 0)
 			return 0;
@@ -573,7 +574,7 @@ int skb_copy_datagram_from_iter(struct sk_buff *skb, int offset,
 
 			if (copy > len)
 				copy = len;
-			copied = copy_page_from_iter(skb_frag_page(frag),
+			copied = copier.copy_page_from_iter(skb_frag_page(frag),
 					  skb_frag_off(frag) + offset - start,
 					  copy, from);
 			if (copied != copy)
@@ -595,9 +596,7 @@ int skb_copy_datagram_from_iter(struct sk_buff *skb, int offset,
 		if ((copy = end - offset) > 0) {
 			if (copy > len)
 				copy = len;
-			if (skb_copy_datagram_from_iter(frag_iter,
-							offset - start,
-							from, copy))
+			if (do_skb_copy_datagram(frag_iter, offset - start, from, copy, copier))
 				goto fault;
 			if ((len -= copy) == 0)
 				return 0;
@@ -611,6 +610,22 @@ int skb_copy_datagram_from_iter(struct sk_buff *skb, int offset,
 fault:
 	return -EFAULT;
 }
+
+/**
+ *	skb_copy_datagram_from_iter - Copy a datagram from an iov_iter.
+ *	@skb: buffer to copy
+ *	@offset: offset in the buffer to start copying to
+ *	@from: the copy source
+ *	@len: amount of data to copy to buffer from iovec
+ *
+ *	Returns 0 or -EFAULT.
+ */
+int skb_copy_datagram_from_iter(struct sk_buff *skb, int offset,
+				struct iov_iter *from,
+				 int len)
+{
+	return do_skb_copy_datagram(skb, offset, from, len, skb_copier);
+}
 EXPORT_SYMBOL(skb_copy_datagram_from_iter);
 
 int __zerocopy_sg_from_iter(struct sock *sk, struct sk_buff *skb,
-- 
2.7.4