Re: [Xen-devel] [PATCH 2/6] xen-netfront: reduce gso_max_size to account for ethernet header

[David Vrabel <david.vrabel@xxxxxxxxxx>]

On 25/03/13 11:08, Wei Liu wrote:
> The maximum packet including ethernet header that can be handled by netfront /
> netback wire format is 65535. Reduce gso_max_size accordingly.
> 
> Drop skb and print warning when skb->len > 65535. This can 1) save the effort
> to send malformed packet to netback, 2) help spotting misconfiguration of
> netfront in the future.
[...]
> --- a/drivers/net/xen-netfront.c
> +++ b/drivers/net/xen-netfront.c
> @@ -547,6 +547,18 @@ static int xennet_start_xmit(struct sk_buff *skb, struct 
> net_device *dev)
>       unsigned int len = skb_headlen(skb);
>       unsigned long flags;
>  
> +     /* Wire format of xen_netif_tx_request only supports skb->len
> +      * < 64K, because size field in xen_netif_tx_request is
> +      * uint16_t. If skb->len is too big, drop it and alert user about
> +      * misconfiguration.
> +      */
> +     if (unlikely(skb->len >= (uint16_t)(~0))) {

Suggest a #define for this maximum added to include/xen/interface/io/netif.h

David

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