netdev - Re: [6/6] [VIRTIO] net: Allow receiving SG packets

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Message-Id: <200804220506.16887.rusty@rustcorp.com.au>
Date:	Tue, 22 Apr 2008 05:06:16 +1000
From:	Rusty Russell <rusty@...tcorp.com.au>
To:	virtualization@...ts.linux-foundation.org
Cc:	Herbert Xu <herbert@...dor.apana.org.au>,
	virtualization@...ts.osdl.org, netdev@...r.kernel.org
Subject: Re: [6/6] [VIRTIO] net: Allow receiving SG packets

On Friday 18 April 2008 13:24:27 Herbert Xu wrote:
> Finally this patch lets virtio_net receive GSO packets in addition
> to sending them.
...
>  static void try_fill_recv(struct virtnet_info *vi)
>  {
>  	struct sk_buff *skb;
> -	struct scatterlist sg[1+MAX_SKB_FRAGS];
> +	struct scatterlist sg[2+MAX_SKB_FRAGS];
>  	int num, err;

I'm not sure what the right number is here.  Say worst case is header which 
goes over a page boundary then MAX_SKB_FRAGS in the skb, but for some reason 
that already has a +2:

/* To allow 64K frame to be packed as single skb without frag_list */
#define MAX_SKB_FRAGS (65536/PAGE_SIZE + 2)

Unless someone explains, I'll change the xmit sg to 2+MAX_SKB_FRAGS as well.

Thanks,
Rusty.
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