Re: [PATCH v5 5/9] net: Define enum for net device features.

[Ben Hutchings <bhutchings@solarflare.com>]

On Wed, 2011-11-16 at 02:29 +0100, Michał Mirosław wrote:
> Define feature values by bit position instead of direct 2**i values
> and force the values to be of type netdev_features_t.
> 
> Cleaned and extended from patch by Mahesh Bandewar <maheshb@google.com>:
> + added netdev_features_t casts
> + included bits under NETIF_F_GSO_MASK
> + moved feature #defines out of struct net_device definition
> 
> Signed-off-by: Michał Mirosław <mirq-linux@rere.qmqm.pl>
> ---
>  include/linux/netdev_features.h |  129 +++++++++++++++++++++++++++-----------
>  1 files changed, 91 insertions(+), 38 deletions(-)
> 
> diff --git a/include/linux/netdev_features.h b/include/linux/netdev_features.h
> index af52381..04ac8f8 100644
> --- a/include/linux/netdev_features.h
> +++ b/include/linux/netdev_features.h
[...]
> +	/**/NETIF_F_GSO_SHIFT,		/* keep the order of SKB_GSO_* bits */
> +	NETIF_F_TSO_BIT			/* ... TCPv4 segmentation */
> +		= NETIF_F_GSO_SHIFT,
> +	NETIF_F_UFO_BIT,		/* ... UDPv4 fragmentation */
> +	NETIF_F_GSO_ROBUST_BIT,		/* ... ->SKB_GSO_DODGY */
> +	NETIF_F_TSO_ECN_BIT,		/* ... TCP ECN support */
> +	NETIF_F_TSO6_BIT,		/* ... TCPv6 segmentation */
> +	NETIF_F_FSO_BIT,		/* ... FCoE segmentation */
> +	NETIF_F_GSO_RESERVED1,		/* ... free (fill GSO_MASK to 8 bits) */
> +	/**/NETIF_F_GSO_LAST,		/* [can't be last bit, see GSO_MASK] */
> +	NETIF_F_GSO_RESERVED2		/* ... free (fill GSO_MASK to 8 bits) */
> +		= NETIF_F_GSO_LAST,
>  
> -/* Segmentation offload features */
> -#define NETIF_F_GSO_SHIFT	16
> -#define NETIF_F_GSO_MASK	0x00ff0000
> -#define NETIF_F_TSO		(SKB_GSO_TCPV4 << NETIF_F_GSO_SHIFT)
> -#define NETIF_F_UFO		(SKB_GSO_UDP << NETIF_F_GSO_SHIFT)
> -#define NETIF_F_GSO_ROBUST	(SKB_GSO_DODGY << NETIF_F_GSO_SHIFT)
> -#define NETIF_F_TSO_ECN		(SKB_GSO_TCP_ECN << NETIF_F_GSO_SHIFT)
> -#define NETIF_F_TSO6		(SKB_GSO_TCPV6 << NETIF_F_GSO_SHIFT)
> -#define NETIF_F_FSO		(SKB_GSO_FCOE << NETIF_F_GSO_SHIFT)
[...]

You should either add BUILD_BUG_ON()s somewhere to ensure that the
netdev feature and skb GSO flags remain in sync, or redefine the skb GSO
flags using the netdev feature flags (which I thought was the reason for
moving features to their own header).

Ben.

-- 
Ben Hutchings, Staff Engineer, Solarflare
Not speaking for my employer; that's the marketing department's job.
They asked us to note that Solarflare product names are trademarked.