[Xen-ia64-devel] RE: [PATCH 06/27] ia64/xen: define NET_SKB_NET to 18 if xen.

[Akio Takebe <takebe_akio@xxxxxxxxxxxxxx>]

Hi, Tony

>> Resolve it by increasing NET_SKB_NET from the default value 16 to 18.
>
>Typo?  You mean NET_SKB_PAD here?
>
I think so. :-)

>But in include/linux/skbuff.h it says: "It must be a power of 2".
>
>Explain why 18 is ok.
It's supposed to add NET_IP_ALIGN when network driver allocs 
skb with netdev_alloc_skb(). For example, e1000 do like the below, too.

struct sk_buff *new_skb = netdev_alloc_skb(netdev, length + NET_IP_ALIGN);

In the case of xen, xen-frontend.c also uses __netdev_alloc_skb(),
so we need to add 16 + NET_IP_ALIGN for padding.
I think we use NET_SKB_PAD=16+NET_IP_ALIGN or
we add it to length of __netdev_alloc_skb().

The below is my patch being relative to this.
http://xenbits.xensource.com/xen-unstable.hg?cs=797430d25f1b

Best Regards,

Akio Takebe


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