netlink: extended ACK reporting

Add the base infrastructure and UAPI for netlink extended ACK
reporting. All "manual" calls to netlink_ack() pass NULL for now and
thus don't get extended ACK reporting.

Big thanks goes to Pablo Neira Ayuso for not only bringing up the
whole topic at netconf (again) but also coming up with the nlattr
passing trick and various other ideas.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Reviewed-by: David Ahern <dsa@cumulusnetworks.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 25 insertions, 1 deletions

diff --git a/include/linux/netlink.h b/include/linux/netlink.h
index da14ab6..60e7137 100644
--- a/include/linux/netlink.h
+++ b/include/linux/netlink.h
@@ -62,11 +62,35 @@ netlink_kernel_create(struct net *net, int unit, struct netlink_kernel_cfg *cfg)
 	return __netlink_kernel_create(net, unit, THIS_MODULE, cfg);
 }
 
+/**
+ * struct netlink_ext_ack - netlink extended ACK report struct
+ * @_msg: message string to report - don't access directly, use
+ *	%NL_SET_ERR_MSG
+ * @bad_attr: attribute with error
+ */
+struct netlink_ext_ack {
+	const char *_msg;
+	const struct nlattr *bad_attr;
+};
+
+/* Always use this macro, this allows later putting the
+ * message into a separate section or such for things
+ * like translation or listing all possible messages.
+ * 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;			\
+} while (0)
+
 extern void netlink_kernel_release(struct sock *sk);
 extern int __netlink_change_ngroups(struct sock *sk, unsigned int groups);
 extern int netlink_change_ngroups(struct sock *sk, unsigned int groups);
 extern void __netlink_clear_multicast_users(struct sock *sk, unsigned int group);
-extern void netlink_ack(struct sk_buff *in_skb, struct nlmsghdr *nlh, int err);
+extern void netlink_ack(struct sk_buff *in_skb, struct nlmsghdr *nlh, int err,
+			const struct netlink_ext_ack *extack);
 extern int netlink_has_listeners(struct sock *sk, unsigned int group);
 
 extern int netlink_unicast(struct sock *ssk, struct sk_buff *skb, __u32 portid, int nonblock);