netdev - [PATCH net-next v4 1/3] netlink: Add nla_put_empty

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Message-ID: <20250207030916.32751-2-jdamato@fastly.com>
Date: Fri,  7 Feb 2025 03:08:53 +0000
From: Joe Damato <jdamato@...tly.com>
To: netdev@...r.kernel.org
Cc: pabeni@...hat.com,
	edumazet@...gle.com,
	sridhar.samudrala@...el.com,
	Joe Damato <jdamato@...tly.com>,
	Jakub Kicinski <kuba@...nel.org>,
	"David S. Miller" <davem@...emloft.net>,
	Simon Horman <horms@...nel.org>,
	linux-kernel@...r.kernel.org (open list)
Subject: [PATCH net-next v4 1/3] netlink: Add nla_put_empty_nest helper

Creating empty nests is helpful when the exact attributes to be exposed
in the future are not known. Encapsulate the logic in a helper.

Signed-off-by: Joe Damato <jdamato@...tly.com>
Suggested-by: Jakub Kicinski <kuba@...nel.org>
---
 v4:
   - new in v4

 include/net/netlink.h | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/include/net/netlink.h b/include/net/netlink.h
index e015ffbed819..29e0db940382 100644
--- a/include/net/netlink.h
+++ b/include/net/netlink.h
@@ -118,6 +118,7 @@
  *   nla_nest_start(skb, type)		start a nested attribute
  *   nla_nest_end(skb, nla)		finalize a nested attribute
  *   nla_nest_cancel(skb, nla)		cancel nested attribute construction
+ *   nla_put_empty_nest(skb, type)	create an empty nest
  *
  * Attribute Length Calculations:
  *   nla_attr_size(payload)		length of attribute w/o padding
@@ -2240,6 +2241,20 @@ static inline void nla_nest_cancel(struct sk_buff *skb, struct nlattr *start)
 	nlmsg_trim(skb, start);
 }
 
+/**
+ * nla_put_empty_nest - Create an empty nest
+ * @skb: socket buffer the message is stored in
+ * @attrtype: attribute type of the container
+ *
+ * This function is a helper for creating empty nests.
+ *
+ * Returns: 0 when successful or -EMSGSIZE on failure.
+ */
+static inline int nla_put_empty_nest(struct sk_buff *skb, int attrtype)
+{
+	return nla_nest_start(skb, attrtype) ? 0 : -EMSGSIZE;
+}
+
 /**
  * __nla_validate_nested - Validate a stream of nested attributes
  * @start: container attribute
-- 
2.43.0