Re: [RFC PATCH net-next 0/3] make nla_nest_start() add NLA_F_NESTED flag

[Jiri Pirko <jiri@resnulli.us>]

Wed, Apr 24, 2019 at 11:34:21PM CEST, mkubecek@suse.cz wrote:
>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.
>
>If this approach is considered too intrusive, we can 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.

I like this. Long overdue...