Subject: Re: [iproute PATCH RFC] libnetlink: introduce DECLARE_NLREQ

From: Stephen Hemminger <[email-masked]>
Date: Sun, 29 Nov 2015 12:07:52 -0800

On Thu, 26 Nov 2015 14:26:05 +0100
Phil Sutter <[email-masked]> wrote:

> This macro aims to simplify most netlink users' pattern to prepare a
> request, which is to create an unnamed struct and initialize it:
> 
> | struct {
> |	struct nlmsghdr n;
> |	struct whatever foo;
> |	char buf[arbitrary number];
> | } req;
> |
> | memset(&req, 0, sizeof(req));
> | req.n.nlmsg_len = NLMSG_LENGTH(sizeof(struct whatever));
> | req.n.nlmsg_flags = NLM_F_REQUEST;
> 
> Having this patch applied, the above can be replaced by a static
> initializer like so:
> 
> | DECLARE_NLREQ(req, n, struct whatever foo, arbitrary number);
> 
> There is an added benefit, as well: Due to explicit alignment, the
> requested tailroom is really as big as requested no matter what size
> struct whatever really is.
> 
> Signed-off-by: Phil Sutter <[email-masked]>
> ---
> This patch is RFC because I want to wait for peer review and upstream
> acceptance before sending in the big refactoring patch itself.
> ---
>  include/libnetlink.h | 11 +++++++++++
>  1 file changed, 11 insertions(+)

I am not a fan of complex macros. But netlink seems to get lots of them.
You need to add more parens round arguments (like name).

Really longterm would rather iproute2 switched to a cleaner library like libmnl