[PATCH 5/7] net/core: Allow the compiler to verify declaration and definition consistency

[Bart Van Assche <bvanassche@acm.org>]

Instead of declaring a function in a .c file, declare it in a header
file and include that header file from the source files that define
and that use the function. That allows the compiler to verify
consistency of declaration and definition. See also commit
52267790ef52 ("sock: add MSG_ZEROCOPY") # v4.14.

Cc: Willem de Bruijn <willemb@google.com>
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
---
 net/core/datagram.c |  2 ++
 net/core/datagram.h | 15 +++++++++++++++
 net/core/skbuff.c   |  5 ++---
 3 files changed, 19 insertions(+), 3 deletions(-)
 create mode 100644 net/core/datagram.h

diff --git a/net/core/datagram.c b/net/core/datagram.c
index b2651bb6d2a3..c42f1f0e62b6 100644
--- a/net/core/datagram.c
+++ b/net/core/datagram.c
@@ -61,6 +61,8 @@
 #include <trace/events/skb.h>
 #include <net/busy_poll.h>
 
+#include "datagram.h"
+
 /*
  *	Is a socket 'connection oriented' ?
  */
diff --git a/net/core/datagram.h b/net/core/datagram.h
new file mode 100644
index 000000000000..bcfb75bfa3b2
--- /dev/null
+++ b/net/core/datagram.h
@@ -0,0 +1,15 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+
+#ifndef _NET_CORE_DATAGRAM_H_
+#define _NET_CORE_DATAGRAM_H_
+
+#include <linux/types.h>
+
+struct sock;
+struct sk_buff;
+struct iov_iter;
+
+int __zerocopy_sg_from_iter(struct sock *sk, struct sk_buff *skb,
+			    struct iov_iter *from, size_t length);
+
+#endif /* _NET_CORE_DATAGRAM_H_ */
diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index 2415d9cb9b89..4782f9354dd1 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -77,6 +77,8 @@
 #include <linux/capability.h>
 #include <linux/user_namespace.h>
 
+#include "datagram.h"
+
 struct kmem_cache *skbuff_head_cache __ro_after_init;
 static struct kmem_cache *skbuff_fclone_cache __ro_after_init;
 #ifdef CONFIG_SKB_EXTENSIONS
@@ -1105,9 +1107,6 @@ void sock_zerocopy_put_abort(struct ubuf_info *uarg, bool have_uref)
 }
 EXPORT_SYMBOL_GPL(sock_zerocopy_put_abort);
 
-extern int __zerocopy_sg_from_iter(struct sock *sk, struct sk_buff *skb,
-				   struct iov_iter *from, size_t length);
-
 int skb_zerocopy_iter_dgram(struct sk_buff *skb, struct msghdr *msg, int len)
 {
 	return __zerocopy_sg_from_iter(skb->sk, skb, &msg->msg_iter, len);
-- 
2.21.0.155.ge902e9bcae20