netdev - Re: [PATCH v2 net-next 2/4] rtnetlink: Add per-netns RTNL.

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Message-ID: <CANn89i+TbWXVMzzHYVWcyiO7rXnDWPMyuSK4g9=_YaX8qrC=QQ@mail.gmail.com>
Date: Fri, 4 Oct 2024 22:59:32 +0200
From: Eric Dumazet <edumazet@...gle.com>
To: Kuniyuki Iwashima <kuniyu@...zon.com>
Cc: davem@...emloft.net, kuba@...nel.org, kuni1840@...il.com, 
	netdev@...r.kernel.org, pabeni@...hat.com
Subject: Re: [PATCH v2 net-next 2/4] rtnetlink: Add per-netns RTNL.

On Fri, Oct 4, 2024 at 10:51 PM Kuniyuki Iwashima <kuniyu@...zon.com> wrote:
>
> From: Kuniyuki Iwashima <kuniyu@...zon.com>
> Date: Fri, 4 Oct 2024 13:45:26 -0700
> > From: Jakub Kicinski <kuba@...nel.org>
> > Date: Fri, 4 Oct 2024 13:21:45 -0700
> > > On Wed, 2 Oct 2024 08:12:38 -0700 Kuniyuki Iwashima wrote:
> > > > +#ifdef CONFIG_DEBUG_NET_SMALL_RTNL
> > > > +void __rtnl_net_lock(struct net *net);
> > > > +void __rtnl_net_unlock(struct net *net);
> > > > +void rtnl_net_lock(struct net *net);
> > > > +void rtnl_net_unlock(struct net *net);
> > > > +int rtnl_net_lock_cmp_fn(const struct lockdep_map *a, const struct lockdep_map *b);
> > > > +#else
> > > > +#define __rtnl_net_lock(net)
> > > > +#define __rtnl_net_unlock(net)
> > > > +#define rtnl_net_lock(net) rtnl_lock()
> > > > +#define rtnl_net_unlock(net) rtnl_unlock()
> > >
> > > Let's make sure net is always evaluated?
> > > At the very least make sure the preprocessor doesn't eat it completely
> > > otherwise we may end up with config-dependent "unused variable"
> > > warnings down the line.
> >
> > Sure, what comes to mind is void casting, which I guess is old-school
> > style ?  Do you have any other idea or is this acceptable ?
> >
> > #define __rtnl_net_lock(net) (void)(net)
> > #define __rtnl_net_unlock(net) (void)(net)
> > #define rtnl_net_lock(net)    \
> >       do {                    \
> >               (void)(net);    \
> >               rtnl_lock();    \
> >       } while (0)
> > #define rtnl_net_unlock(net)  \
> >       do {                    \
> >               (void)(net);    \
> >               rtnl_unlock();  \
> >       } while (0)
>
> or simply define these as static inline functions and
> probably this is more preferable ?
>
> static inline void __rtnl_net_lock(struct net *net) {}
> static inline void __rtnl_net_unlock(struct net *net) {}
> static inline void rtnl_net_lock(struct net *net)
> {
>         rtnl_lock();
> }
> static inline void rtnl_net_unlock(struct net *net)
> {
>         rtnl_unlock();
> }

static inline functions seem better to me.