[4/8] ethoc: prevent overflow of rx counter

Rewind cur_rx to prevent it from overflowing.

Signed-off-by: Jonas Bonn <jonas@southpole.se>
---
 drivers/net/ethoc.c |    3 +++
 1 files changed, 3 insertions(+), 0 deletions(-)

On Wed, 2010-11-24 at 14:40 +0100, Jonas Bonn wrote:
> Rewind cur_rx to prevent it from overflowing.
> 
> Signed-off-by: Jonas Bonn <jonas@southpole.se>
> ---
>  drivers/net/ethoc.c |    3 +++
>  1 files changed, 3 insertions(+), 0 deletions(-)
> 
> diff --git a/drivers/net/ethoc.c b/drivers/net/ethoc.c
> index 53c03f2..7d1b5d8 100644
> --- a/drivers/net/ethoc.c
> +++ b/drivers/net/ethoc.c
> @@ -408,6 +408,9 @@ static int ethoc_rx(struct net_device *dev, int limit)
>  	struct ethoc *priv = netdev_priv(dev);
>  	int count;
>  
> +	/* Prevent overflow of priv->cur_rx by rewinding it */	
> +	priv->cur_rx = priv->cur_rx % priv->num_rx;
> +

Division is expensive; you should either use masking (if priv->num_rx is
guaranteed to be a power of 2) or check for overflow whenever you
increment priv->cur_rx:

	if (++priv->cur_rx == priv->num_rx)
		priv->cur_rx = 0;

Ben.

>  	for (count = 0; count < limit; ++count) {
>  		unsigned int entry;
>  		struct ethoc_bd bd;

From: Jonas Bonn <jonas@southpole.se>
Date: Wed, 24 Nov 2010 14:40:54 +0100

> Rewind cur_rx to prevent it from overflowing.
> 
> Signed-off-by: Jonas Bonn <jonas@southpole.se>
...
> +	/* Prevent overflow of priv->cur_rx by rewinding it */	

Trailing whitespace, also please integrate the feedback from Ben
and Eric Dumazet about making this computation less expensive.
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