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

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Message-ID: <20111116233408.GB8476@rere.qmqm.pl>
Date:	Thu, 17 Nov 2011 00:34:08 +0100
From:	Michał Mirosław <mirq-linux@...e.qmqm.pl>
To:	Ben Hutchings <bhutchings@...arflare.com>
Cc:	netdev@...r.kernel.org, "David S. Miller" <davem@...emloft.net>
Subject: Re: [PATCH v5 5/9] net: Define enum for net device features.

On Wed, Nov 16, 2011 at 10:39:37PM +0000, Ben Hutchings wrote:
> 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@...gle.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@...e.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).

Main motiviation for the moving out of features to separate headers was
to avoid circular inclusion of linux/netdevice.h from linux/skbuff.h.
We get readability for free.

BUILD_BUG_ON() is a good idea. It should go to skbuff.h and as separate
patch as it's something new and independent.

Best Regards,
Michał Mirosław
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