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

[Wei Liu <wei.liu2@xxxxxxxxxx>]

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@xxxxxxxxxx>
> > ---
> >  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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