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

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Date:	Thu, 11 Jul 2013 12:12:24 +0100
From:	Ian Campbell <ian.campbell@...rix.com>
To:	Annie <annie.li@...cle.com>
CC:	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"xen-devel@...ts.xensource.com" <xen-devel@...ts.xensource.com>,
	"wei.liu2@...rix.com" <wei.liu2@...rix.com>,
	"msw@...zon.com" <msw@...zon.com>
Subject: Re: [Xen-devel] [PATCH v2 1/1] xen/netback: correctly calculate
 required slots of skb.


> 
> > 
> > 
> > > 
> > > > 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);

Ian


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