netdev - Re: [PATCH net-next 4/5] nfp: add .ndo_get

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Date:   Fri, 22 Feb 2019 10:53:26 -0800
From:   Jakub Kicinski <jakub.kicinski@...ronome.com>
To:     Michal Kubecek <mkubecek@...e.cz>
Cc:     davem@...emloft.net, jiri@...nulli.us, andrew@...n.ch,
        f.fainelli@...il.com, netdev@...r.kernel.org,
        oss-drivers@...ronome.com
Subject: Re: [PATCH net-next 4/5] nfp: add .ndo_get_devlink

On Fri, 22 Feb 2019 18:27:15 +0100, Michal Kubecek wrote:
> > > Maybe it would be safer not to call ndo_get_devlink directly and have
> > > an inline wrapper like
> > > 
> > > #if IS_ENABLED(CONFIG_NET_DEVLINK)
> > > static inline struct devlink *dev_get_devlink(struct net_device *dev)
> > > {
> > > 	if (dev->netdev_ops->ndo_get_devlink)
> > > 		return dev->netdev_ops->ndo_get_devlink();
> > > 	else
> > > 		retrurn NULL;
> > > }
> > > #else
> > > static inline struct devlink *dev_get_devlink(struct net_device *dev)
> > > {
> > > 	return NULL;
> > > }
> > > #endif
> > > 
> > > so that one can simply call the wrapper and check return value for NULL.  
> > 
> > Only devlink code can call this ndo, and it doesn't exist with
> > DEVLINK=n.  I don't dislike wrappers for NDOs, but I'll defer to Jiri
> > to decide if we want a wrapper here (without the #if/#else, just the
> > first part for code clarity) :)  
> 
> If the NDO is only supposed to be called from devlink code (or, more
> precisely, code built only with CONFIG_DEVLINK=y), it should be IMHO
> mentioned in its description. Another option would be enforcing it by
> adding #ifdef around the ndo_get_devlink entry in struct net_device_ops
> but that would require using ifdefs also in each driver providing the
> NDO which seems inconvenient.

Yes, let's just go with your first proposal of a static inline helper.
I think it's the cleanest solution.