netdev - Re: [iproute PATCH RFC] libnetlink: introduce DECLARE

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Message-Id: <20151129213925.87398213E1@mail.nwl.cc>
Date:	Sun, 29 Nov 2015 22:40:44 +0100
From:	Phil Sutter <phil@....cc>
To:	Stephen Hemminger <shemming@...cade.com>
Cc:	netdev@...r.kernel.org
Subject: Re: [iproute PATCH RFC] libnetlink: introduce DECLARE_NLREQ

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On Sun, Nov 29, 2015 at 12:07:52PM -0800, Stephen Hemminger wrote:
> On Thu, 26 Nov 2015 14:26:05 +0100
> Phil Sutter <phil@....cc> 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 <phil@....cc>
> > ---
> > 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

Ah, indeed! Someone else suggested that once, as well. I'll have a look
into that before continuing this path.

Thanks, Phil
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