Subject: Re: [PATCH net-next] net: core: Assert the size of netdev_featres_t

From: Stephen Hemminger <[email-masked]>
Date: Mon, 30 Apr 2018 09:42:10 -0700

On Fri, 27 Apr 2018 13:11:14 -0700
Florian Fainelli <[email-masked]> wrote:

> We have about 53 netdev_features_t bits defined and counting, add a
> build time check to catch when an u64 type will not be enough and we
> will have to convert that to a bitmap. This is done in
> register_netdevice() for convenience.
> 
> Signed-off-by: Florian Fainelli <[email-masked]>
> ---
>  include/linux/netdevice.h | 6 ++++++
>  net/core/dev.c            | 1 +
>  2 files changed, 7 insertions(+)
> 
> diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
> index 366c32891158..4326bc6b27d1 100644
> --- a/include/linux/netdevice.h
> +++ b/include/linux/netdevice.h
> @@ -4121,6 +4121,12 @@ const char *netdev_drivername(const struct net_device *dev);
>  
>  void linkwatch_run_queue(void);
>  
> +static inline void netdev_features_size_check(void)
> +{
> +	BUILD_BUG_ON(sizeof(netdev_features_t) * BITS_PER_BYTE <
> +		     NETDEV_FEATURE_COUNT);
> +}
> +
>  static inline netdev_features_t netdev_intersect_features(netdev_features_t f1,
>  							  netdev_features_t f2)
>  {
> diff --git a/net/core/dev.c b/net/core/dev.c
> index 0a2d46424069..23e6c1aa78c6 100644
> --- a/net/core/dev.c
> +++ b/net/core/dev.c
> @@ -7881,6 +7881,7 @@ int register_netdevice(struct net_device *dev)
>  	int ret;
>  	struct net *net = dev_net(dev);
>  
> +	netdev_features_size_check();
>  	BUG_ON(dev_boot_phase);
>  	ASSERT_RTNL();
>  

You don't have do this kind of inline function stuff to get the check.
Why not just put BUILD_BUG_ON directly in net/core/dev.c  Could be anywhere.
Rather than adding inline in the header file.