netdev - Re: [PATCH 1/4] xen-netfront: remove unused variable `extra'

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Date:	Mon, 18 Mar 2013 12:04:31 +0000
From:	Wei Liu <wei.liu2@...rix.com>
To:	Ian Campbell <Ian.Campbell@...rix.com>
CC:	<wei.liu2@...rix.com>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"xen-devel@...ts.xen.org" <xen-devel@...ts.xen.org>,
	"konrad.wilk@...cle.com" <konrad.wilk@...cle.com>,
	"annie.li@...cle.com" <annie.li@...cle.com>
Subject: Re: [PATCH 1/4] xen-netfront: remove unused variable `extra'

On Mon, 2013-03-18 at 11:42 +0000, Ian Campbell wrote:
> On Mon, 2013-03-18 at 10:35 +0000, Wei Liu wrote:
> 
> I think a few more words are needed here since from the code you are
> removing it seems very much like gso is used for something. If you have
> a proof that the "extra = gso" case is never hit then please explain it.
> Perhaps a reference to the removal of the last user?
> 
> Or maybe it is the case that it should be used and the bug is that it
> isn't?
> 

Looks like the latter one. 'extra' field should  be used to get hold of
the last extra info in the ring. ;-)

But, the only extra info in upstream kernel is XEN_NETIF_EXTRA_TYPE_GSO,
so there's really no other extra info in the ring at that point. Could
it be possible that it is something from classic Xen kernel?


Wei.

> > Signed-off-by: Wei Liu <wei.liu2@...rix.com>
> > ---
> >  drivers/net/xen-netfront.c |    8 +-------
> >  1 file changed, 1 insertion(+), 7 deletions(-)
> > 
> > diff --git a/drivers/net/xen-netfront.c b/drivers/net/xen-netfront.c
> > index 7ffa43b..5527663 100644
> > --- a/drivers/net/xen-netfront.c
> > +++ b/drivers/net/xen-netfront.c
> > @@ -537,7 +537,6 @@ static int xennet_start_xmit(struct sk_buff *skb, struct net_device *dev)
> >  	struct netfront_info *np = netdev_priv(dev);
> >  	struct netfront_stats *stats = this_cpu_ptr(np->stats);
> >  	struct xen_netif_tx_request *tx;
> > -	struct xen_netif_extra_info *extra;
> >  	char *data = skb->data;
> >  	RING_IDX i;
> >  	grant_ref_t ref;
> > @@ -581,7 +580,6 @@ static int xennet_start_xmit(struct sk_buff *skb, struct net_device *dev)
> >  	tx->gref = np->grant_tx_ref[id] = ref;
> >  	tx->offset = offset;
> >  	tx->size = len;
> > -	extra = NULL;
> >  
> >  	tx->flags = 0;
> >  	if (skb->ip_summed == CHECKSUM_PARTIAL)
> > @@ -597,10 +595,7 @@ static int xennet_start_xmit(struct sk_buff *skb, struct net_device *dev)
> >  		gso = (struct xen_netif_extra_info *)
> >  			RING_GET_REQUEST(&np->tx, ++i);
> >  
> > -		if (extra)
> > -			extra->flags |= XEN_NETIF_EXTRA_FLAG_MORE;
> > -		else
> > -			tx->flags |= XEN_NETTXF_extra_info;
> > +		tx->flags |= XEN_NETTXF_extra_info;
> >  
> >  		gso->u.gso.size = skb_shinfo(skb)->gso_size;
> >  		gso->u.gso.type = XEN_NETIF_GSO_TYPE_TCPV4;
> > @@ -609,7 +604,6 @@ static int xennet_start_xmit(struct sk_buff *skb, struct net_device *dev)
> >  
> >  		gso->type = XEN_NETIF_EXTRA_TYPE_GSO;
> >  		gso->flags = 0;
> > -		extra = gso;
> >  	}
> >  
> >  	np->tx.req_prod_pvt = i + 1;
> 
> 


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