Merge branch 'nla_nest_start'

Michal Kubecek says:

====================
make nla_nest_start() add NLA_F_NESTED flag

One of the comments in recent review of the ethtool netlink series pointed
out that proposed ethnl_nest_start() helper which adds NLA_F_NESTED to
second argument of nla_nest_start() is not really specific to ethtool
netlink code. That is hard to argue with as closer inspection revealed that
exactly the same helper already exists in ipset code (except it's a macro
rather than an inline function).

Another observation was that even if NLA_F_NESTED flag was introduced in
2007, only few netlink based interfaces set it in kernel generated messages
and even many recently added APIs omit it. That is unfortunate as without
the flag, message parsers not familiar with attribute semantics cannot
recognize nested attributes and do not see message structure; this affects
e.g. wireshark dissector or mnl_nlmsg_fprintf() from libmnl.

This is why I'm suggesting to rename existing nla_nest_start() to different
name (nla_nest_start_noflag) and reintroduce nla_nest_start() as a wrapper
adding NLA_F_NESTED flag. This is implemented in first patch which is
mostly generated by spatch. Second patch drops ipset helper macros which
lose their purpose. Third patch cleans up minor coding style issues found
by checkpatch.pl in first patch.

We could leave nla_nest_start() untouched and simply add a wrapper adding
NLA_F_NESTED but that would probably preserve the state when even most new
code doesn't set the flag.
====================

Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 23 insertions, 3 deletions

diff --git a/include/net/netlink.h b/include/net/netlink.h
index 23f27b0b3cef..1f18b47f41b4 100644
--- a/include/net/netlink.h
+++ b/include/net/netlink.h
@@ -1415,13 +1415,18 @@ static inline void *nla_memdup(const struct nlattr *src, gfp_t gfp)
 }
 
 /**
- * nla_nest_start - Start a new level of nested attributes
+ * nla_nest_start_noflag - Start a new level of nested attributes
  * @skb: socket buffer to add attributes to
  * @attrtype: attribute type of container
  *
- * Returns the container attribute
+ * This function exists for backward compatibility to use in APIs which never
+ * marked their nest attributes with NLA_F_NESTED flag. New APIs should use
+ * nla_nest_start() which sets the flag.
+ *
+ * Returns the container attribute or NULL on error
  */
-static inline struct nlattr *nla_nest_start(struct sk_buff *skb, int attrtype)
+static inline struct nlattr *nla_nest_start_noflag(struct sk_buff *skb,
+						   int attrtype)
 {
 	struct nlattr *start = (struct nlattr *)skb_tail_pointer(skb);
 
@@ -1432,6 +1437,21 @@ static inline struct nlattr *nla_nest_start(struct sk_buff *skb, int attrtype)
 }
 
 /**
+ * nla_nest_start - Start a new level of nested attributes, with NLA_F_NESTED
+ * @skb: socket buffer to add attributes to
+ * @attrtype: attribute type of container
+ *
+ * Unlike nla_nest_start_noflag(), mark the nest attribute with NLA_F_NESTED
+ * flag. This is the preferred function to use in new code.
+ *
+ * Returns the container attribute or NULL on error
+ */
+static inline struct nlattr *nla_nest_start(struct sk_buff *skb, int attrtype)
+{
+	return nla_nest_start_noflag(skb, attrtype | NLA_F_NESTED);
+}
+
+/**
  * nla_nest_end - Finalize nesting of attributes
  * @skb: socket buffer the attributes are stored in
  * @start: container attribute