[PATCH 1/2] net: Introduce skb_copy_datagram_from_iter_full()

[Will Deacon <will@kernel.org>]

In a similar manner to copy_from_iter()/copy_from_iter_full(), introduce
skb_copy_datagram_from_iter_full() which reverts the iterator to its
initial state when returning an error.

A subsequent fix for a vsock regression will make use of this new
function.

Cc: Paolo Abeni <pabeni@redhat.com>
Cc: Christian Brauner <brauner@kernel.org>
Cc: Eric Dumazet <edumazet@google.com>
Cc: Jakub Kicinski <kuba@kernel.org>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Will Deacon <will@kernel.org>
---
 include/linux/skbuff.h |  2 ++
 net/core/datagram.c    | 14 ++++++++++++++
 2 files changed, 16 insertions(+)

diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index 14b923ddb6df..fa633657e4c0 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -4172,6 +4172,8 @@ int skb_copy_and_crc32c_datagram_iter(const struct sk_buff *skb, int offset,
 				      struct iov_iter *to, int len, u32 *crcp);
 int skb_copy_datagram_from_iter(struct sk_buff *skb, int offset,
 				 struct iov_iter *from, int len);
+int skb_copy_datagram_from_iter_full(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);
 int skb_kill_datagram(struct sock *sk, struct sk_buff *skb, unsigned int flags);
diff --git a/net/core/datagram.c b/net/core/datagram.c
index 94cc4705e91d..f474b9b120f9 100644
--- a/net/core/datagram.c
+++ b/net/core/datagram.c
@@ -618,6 +618,20 @@ int skb_copy_datagram_from_iter(struct sk_buff *skb, int offset,
 }
 EXPORT_SYMBOL(skb_copy_datagram_from_iter);
 
+int skb_copy_datagram_from_iter_full(struct sk_buff *skb, int offset,
+				     struct iov_iter *from, int len)
+{
+	struct iov_iter_state state;
+	int ret;
+
+	iov_iter_save_state(from, &state);
+	ret = skb_copy_datagram_from_iter(skb, offset, from, len);
+	if (ret)
+		iov_iter_restore(from, &state);
+	return ret;
+}
+EXPORT_SYMBOL(skb_copy_datagram_from_iter_full);
+
 int zerocopy_fill_skb_from_iter(struct sk_buff *skb,
 				struct iov_iter *from, size_t length)
 {
-- 
2.51.0.rc1.167.g924127e9c0-goog