netlink: add helpers for extack attr presence checking

Being able to check attribute presence and set extack
if not on one line is handy, add helpers.
Reviewed-by: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

include/linux/netlink.h

@@ -139,6 +139,17 @@ struct netlink_ext_ack {
 	}						\
 } while (0)
 
+#define NL_REQ_ATTR_CHECK(extack, nest, tb, type) ({		\
+	struct nlattr **__tb = (tb);				\
+	u32 __attr = (type);					\
+	int __retval;						\
+								\
+	__retval = !__tb[__attr];				\
+	if (__retval)						\
+		NL_SET_ERR_ATTR_MISS((extack), (nest), __attr);	\
+	__retval;						\
+})
+
 static inline void nl_set_extack_cookie_u64(struct netlink_ext_ack *extack,
 					    u64 cookie)
 {

include/net/genetlink.h

@@ -110,6 +110,13 @@ static inline void genl_info_net_set(struct genl_info *info, struct net *net)
 
 #define GENL_SET_ERR_MSG(info, msg) NL_SET_ERR_MSG((info)->extack, msg)
 
+/* Report that a root attribute is missing */
+#define GENL_REQ_ATTR_CHECK(info, attr) ({				\
+	struct genl_info *__info = (info);				\
+									\
+	NL_REQ_ATTR_CHECK(__info->extack, NULL, __info->attrs, (attr)); \
+})
+
 enum genl_validate_flags {
 	GENL_DONT_VALIDATE_STRICT		= BIT(0),
 	GENL_DONT_VALIDATE_DUMP			= BIT(1),