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Re: [Xen-devel] [PATCH net-next v3 6/9] xen-netback: Handle guests with too many frags



On 08/01/14 13:54, Eric Dumazet wrote:
On Wed, 2014-01-08 at 13:49 +0000, Zoltan Kiss wrote:
On 08/01/14 02:12, Eric Dumazet wrote:
On Wed, 2014-01-08 at 00:10 +0000, Zoltan Kiss wrote:


+               if (skb_shinfo(skb)->frag_list) {
+                       nskb = skb_shinfo(skb)->frag_list;
+                       xenvif_fill_frags(vif, nskb, INVALID_PENDING_IDX);
+                       skb->len += nskb->len;
+                       skb->data_len += nskb->len;
+                       skb->truesize += nskb->truesize;
+                       skb_shinfo(skb)->tx_flags |= SKBTX_DEV_ZEROCOPY;
+                       skb_shinfo(nskb)->tx_flags |= SKBTX_DEV_ZEROCOPY;
+                       vif->tx_zerocopy_sent += 2;
+                       nskb = skb;
+
+                       skb = skb_copy_expand(skb,
+                                       0,
+                                       0,
+                                       GFP_ATOMIC | __GFP_NOWARN);

skb can be NULL here

Thanks, fixed that.

BTW, I am not sure why you copy the skb.

Is it to get rid of frag_list, and why ?

Yes, it is to get rid of the frag_list, just to be on the safe side. I'm not sure if it is normal to send a big skb with MAX_SKB_FRAGS frags plus an empty skb on the frag_list with one frag, so I just consolidate them here. This scenario shouldn't happen very often anyway, even guests which can send more than MAX_SKB_FRAGS slots tends to do it rarely.

Zoli


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