Subject: Re: [net-next PATCH 1/5] etherdevice: Add function for handling padding frame to ETH_ZLEN

From: Florian Fainelli <[email-masked]>
Date: Tue, 25 Nov 2014 16:56:05 -0800

On 25/11/14 14:44, Alexander Duyck wrote:
> This patch adds a simple function for padding a frame up to the minimum
> size for for Ethernet.  The motivation behind it is that there are a number
> of implementations throughout the network device drivers that are all doing
> the same thing, but each a little bit differently and as a result several
> implementations contain bugs such as updating the length without updating
> the tail offset and other similar issues.
> 
> Signed-off-by: Alexander Duyck <[email-masked]>
> ---
>  include/linux/etherdevice.h |   21 +++++++++++++++++++++
>  1 file changed, 21 insertions(+)
> 
> diff --git a/include/linux/etherdevice.h b/include/linux/etherdevice.h
> index 733980f..7e436f3 100644
> --- a/include/linux/etherdevice.h
> +++ b/include/linux/etherdevice.h
> @@ -392,4 +392,25 @@ static inline unsigned long compare_ether_header(const void *a, const void *b)
>  #endif
>  }
>  
> +/**
> + * eth_skb_pad - Pad buffer to mininum number of octets for Ethernet frame
> + * @skb: Buffer to pad
> + *
> + * An Ethernet frame should have a minimum size of 60 bytes.  This function
> + * takes short frames and pads them with zeros up to the 60 byte limit.

minimum size without FCS

> + */
> +static inline int eth_skb_pad(struct sk_buff *skb)
> +{
> +	unsigned int size = skb->len;
> +
> +	if (unlikely(size < ETH_ZLEN)) {
> +		size = ETH_ZLEN - size;
> +		if (skb_pad(skb, size))
> +			return -ENOMEM;
> +		__skb_put(skb, size);
> +	}

most drivers call skb_padto(skb, ETH_ZLEN), besides the extra
__skb_put() here, this is not different.

> +
> +	return 0;
> +}
> +
>  #endif	/* _LINUX_ETHERDEVICE_H */
> 
> --
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