Re: [Xen-devel] [PATCH v2 1/1] xen/netback: correctly calculate required slots of skb.

[annie li <annie.li@xxxxxxxxxx>]

On 2013-7-11 19:12, Ian Campbell wrote:
> > > > > The code here only
> > > > > increase count for the first time. I thought to initialize the
> > > > > count in
> > > > > xen_netbk_count_skb_slots with 1 to avoid this. But thinking of
> > > > > the
> > > > > extreme case when the header size is zero(not sure whether this
> > > > > case
> > > > > could be true), I increase the count here to keep safe in case
> > > > > header
> > > > > size is zero.
> > > > netfront requires that the first slot always contains some data,
> > > > gop_frag_copy will BUG if that's not the case.
> > In gop_frag_copy, we can not go into the while if the size is 0. Which
> > BUG_ON do you mean here?
> in gop_frag_copy:
>                 if (start_new_rx_buffer(npo->copy_off, bytes, *head)) {
>                         /*
>                          * Netfront requires there to be some data in the head
>                          * buffer.
>                          */
>                         BUG_ON(*head);
But If there is SKB with zero header size and zero offset, the code will 
not run into the while loop in gop_frag_copy and this if condition. 
BUG_ON will not happen in such situation.
Thanks
Annie

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