Re: [janitor] remove casts in drivers/net/arm/

[Jeff Garzik <jgarzik@xxxxxxxxx>]

Randy.Dunlap wrote:
> On Tue, 02 Mar 2004 13:54:36 -0500 Jeff Garzik wrote:
>
> | Russell King wrote:
> | > On Sun, Feb 29, 2004 at 02:34:36PM -0800, Randy.Dunlap wrote:
> | > 
> | >> drivers/net/arm/am79c961a.c |   18 +++++++++---------
> | >> drivers/net/arm/ether1.c    |   18 +++++++++---------
> | >> drivers/net/arm/ether3.c    |   18 +++++++++---------
> | >> drivers/net/arm/etherh.c    |    4 ++--
> | >> 4 files changed, 29 insertions(+), 29 deletions(-)
> | > 
> | > 
> | > I think we should really consider using netdev_priv() in all these places
> | > so the compiler knows that 'dev' and 'priv' are related.
> | 
> | 
> | Good point.
> I respectfully disagree, but if the maintainter won't merge
> them as is, so be it.
>
> I have trouble understanding why this:
>         return (char *)dev + ((sizeof(struct net_device) + 31) & ~31);
> is better than using a structure->field, i.e.,
>         dev->priv
>
> Can one of you enlighten me?

One is an additional pointer load and dereference, and one is a constant 
offset from the beginning of the dev structure, calculated at compile 
time.  netdev_priv() provides the same results as dev->priv but at less 
cost.
        Jeff