netdev - [RFC 1/4] netlink: make extended ACK setting NULL-friendly

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Date:   Tue, 25 Apr 2017 01:06:41 -0700
From:   Jakub Kicinski <jakub.kicinski@...ronome.com>
To:     netdev@...r.kernel.org
Cc:     davem@...emloft.net, johannes@...solutions.net,
        dsa@...ulusnetworks.com, daniel@...earbox.net,
        alexei.starovoitov@...il.com, bblanco@...il.com,
        john.fastabend@...il.com, kubakici@...pl,
        oss-drivers@...ronome.com,
        Jakub Kicinski <jakub.kicinski@...ronome.com>
Subject: [RFC 1/4] netlink: make extended ACK setting NULL-friendly

As we propagate extended ack reporting throughout various paths in
the kernel it may happen that the same function is called with the
extended ack parameter passed as NULL.  Make the NL_SET_ERR_MSG()
macro simply print the message to the logs if that happens.

Signed-off-by: Jakub Kicinski <jakub.kicinski@...ronome.com>
---
 include/linux/netlink.h | 12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

diff --git a/include/linux/netlink.h b/include/linux/netlink.h
index 8d2a8924705c..b59cfbf2e2c7 100644
--- a/include/linux/netlink.h
+++ b/include/linux/netlink.h
@@ -86,10 +86,14 @@ struct netlink_ext_ack {
  * Currently string formatting is not supported (due
  * to the lack of an output buffer.)
  */
-#define NL_SET_ERR_MSG(extack, msg) do {	\
-	static const char _msg[] = (msg);	\
-						\
-	(extack)->_msg = _msg;			\
+#define NL_SET_ERR_MSG(extack, msg) do {		\
+	struct netlink_ext_ack *_extack = (extack);	\
+	static const char _msg[] = (msg);		\
+							\
+	if (_extack)					\
+		_extack->_msg = _msg;			\
+	else						\
+		pr_info("%s\n", _msg);			\
 } while (0)
 
 extern void netlink_kernel_release(struct sock *sk);
-- 
2.11.0