[ofa-general] Re: [PATCH] IB/ipoib: fix thinko in packet length checks

[Michael S. Tsirkin]

> Quoting Michael S. Tsirkin <mst at dev.mellanox.co.il>:
> Subject: Re: [PATCH] IB/ipoib: fix thinko in packet length checks
> 
> > Quoting Roland Dreier <rdreier at cisco.com>:
> > Subject: Re: [PATCH] IB/ipoib: fix thinko in packet length checks
> > 
> > This definitely looks like a problem, but I'm confused by this:
> > 
> >  > --- a/drivers/infiniband/ulp/ipoib/ipoib_cm.c
> >  > +++ b/drivers/infiniband/ulp/ipoib/ipoib_cm.c
> >  > @@ -452,7 +452,7 @@ void ipoib_cm_send(struct net_device *dev, struct sk_buff *skb, struct ipoib_cm_
> >  >  			   skb->len, tx->mtu);
> >  >  		++priv->stats.tx_dropped;
> >  >  		++priv->stats.tx_errors;
> >  > -		ipoib_cm_skb_too_long(dev, skb, tx->mtu - INFINIBAND_ALEN);
> >  > +		ipoib_cm_skb_too_long(dev, skb, tx->mtu - IPOIB_ENCAP_LEN);
> >  >  		return;
> >  >  	}
> > 
> > After this change, the code looks like:
> > 
> > 	if (unlikely(skb->len > tx->mtu)) {
> > 		ipoib_warn(priv, "packet len %d (> %d) too long to send, dropping\n",
> > 			   skb->len, tx->mtu);
> > 		++priv->stats.tx_dropped;
> > 		++priv->stats.tx_errors;
> > 		ipoib_cm_skb_too_long(dev, skb, tx->mtu - IPOIB_ENCAP_LEN);
> > 		return;
> > 	}
> > 
> > so why is the test against just tx->mtu, while ipoib_cm_skb_too_long()
> > is passed an mtu of tx->mtu - IPOIB_ENCAP_LEN?
> 
> I actually copied this from datagram code.
> 
> What ipoib_cm_skb_too_long does is set the dest MTU metric.
> 
> So look at this logic in datagram mode:
> 	if (new_mtu > IPOIB_PACKET_SIZE - IPOIB_ENCAP_LEN) {
> 		return -EINVAL;
> 	}
> 
> Why is the max MTU set to IPOIB_PACKET_SIZE - IPOIB_ENCAP_LEN and
> not to IPOIB_PACKET_SIZE?

And by the way, the chunk in the datagram part looks the same.


-- 
MST