netdev - Re: [PATCH v2.41 5/5] datapath: Add basic MPLS support to kernel

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Date:	Wed, 2 Oct 2013 09:40:57 +0900
From:	Simon Horman <horms@...ge.net.au>
To:	Jesse Gross <jesse@...ira.com>
Cc:	"dev@...nvswitch.org" <dev@...nvswitch.org>,
	netdev <netdev@...r.kernel.org>, Ben Pfaff <blp@...ira.com>,
	Pravin B Shelar <pshelar@...ira.com>,
	Ravi K <rkerur@...il.com>,
	Isaku Yamahata <yamahata@...inux.co.jp>,
	Joe Stringer <joe@...d.net.nz>
Subject: Re: [PATCH v2.41 5/5] datapath: Add basic MPLS support to kernel

On Tue, Oct 01, 2013 at 04:02:17PM -0700, Jesse Gross wrote:
> On Mon, Sep 30, 2013 at 11:47 PM, Simon Horman <horms@...ge.net.au> wrote:
> > diff --git a/datapath/actions.c b/datapath/actions.c
> > index d961e5d..bfab9ec 100644
> > --- a/datapath/actions.c
> > +++ b/datapath/actions.c
> > +/* Push MPLS after the ethernet header. */
> > +static int push_mpls(struct sk_buff *skb,
> > +                    const struct ovs_action_push_mpls *mpls)
> [...]
> > +       hdr = eth_hdr(skb);
> > +       hdr->h_proto = mpls->mpls_ethertype;
> > +       if (!eth_p_mpls(skb->protocol) && !ovs_skb_get_inner_protocol(skb))
> > +               ovs_skb_set_inner_protocol(skb, skb->protocol);
> 
> Do we actually need the check for !eth_p_mpls(skb->protocol)? It's not
> clear to me what condition it is trying to prevent.

True, it does not seem useful.
I will remove it.

> > +static int pop_mpls(struct sk_buff *skb, const __be16 ethertype)
> > +{
> > +       struct ethhdr *hdr;
> > +       int err;
> > +
> > +       err = make_writable(skb, skb->mac_len + MPLS_HLEN);
> > +       if (unlikely(err))
> > +               return err;
> > +
> > +       if (unlikely(skb->len < skb->mac_len + MPLS_HLEN))
> > +               return -ENOMEM;
> 
> I'm not sure that this is the right error code in this situation -
> maybe -EINVAL would be better.

I was a bit unsure what was an appropriate value but
I agree that -EINVAL seems better than -ENOMEM.
I will change it to -EINVAL.

> 
> > @@ -545,6 +662,14 @@ static int do_execute_actions(struct datapath *dp, struct sk_buff *skb,
> >                         output_userspace(dp, skb, a);
> >                         break;
> >
> > +               case OVS_ACTION_ATTR_PUSH_MPLS:
> > +                       err = push_mpls(skb, nla_data(a));
> > +                       break;
> > +
> > +               case OVS_ACTION_ATTR_POP_MPLS:
> > +                       err = pop_mpls(skb, nla_get_be16(a));
> > +                       break;
> 
> I think we need something similar to POP_VLAN here - in the event of
> an error the skb will have already been freed.

Thanks, though I think you mean that PUSH_MPLS should be similar to
PUSH_VLAN. I don't think that either pop_mpls() or pop_vlan() free the
skb on error.

I will add the following:

diff --git a/datapath/actions.c b/datapath/actions.c
index bfab9ec..8babfc4 100644
--- a/datapath/actions.c
+++ b/datapath/actions.c
@@ -664,6 +664,8 @@ static int do_execute_actions(struct datapath *dp, struct sk_buff *skb,
 
 		case OVS_ACTION_ATTR_PUSH_MPLS:
 			err = push_mpls(skb, nla_data(a));
+			if (unlikely(err)) /* skb already freed. */
+				return err;
 			break;
 
 		case OVS_ACTION_ATTR_POP_MPLS:

> 
> > diff --git a/datapath/datapath.h b/datapath/datapath.h
> > index 4a49a7d..31fe10a 100644
> > --- a/datapath/datapath.h
> > +++ b/datapath/datapath.h
> > @@ -95,6 +95,8 @@ struct datapath {
> >   * @pkt_key: The flow information extracted from the packet.  Must be nonnull.
> >   * @tun_key: Key for the tunnel that encapsulated this packet. NULL if the
> >   * packet is not being tunneled.
> > + * @inner_protocol: Provides a substitute for the skb->inner_protocol field on
> > + * kernels before 3.11.
> >   */
> >  struct ovs_skb_cb {
> >         struct sw_flow          *flow;
> 
> I think this comment no longer applies now that inner_protocol has
> been moved into the GSO struct.

Thanks, I'll clean that up.

> > diff --git a/datapath/linux/compat/gso.c b/datapath/linux/compat/gso.c
> > index 32f906c..f917356 100644
> > --- a/datapath/linux/compat/gso.c
> > +++ b/datapath/linux/compat/gso.c
> >  int rpl_dev_queue_xmit(struct sk_buff *skb)
> >  {
> >  #undef dev_queue_xmit
> >         int err = -ENOMEM;
> > +       __be16 inner_protocol;
> > +       bool vlan, mpls;
> >
> > -       if (vlan_tx_tag_present(skb) && !dev_supports_vlan_tx(skb->dev)) {
> > +       vlan = mpls = false;
> > +
> > +       inner_protocol = ovs_skb_get_inner_protocol(skb);
> 
> I don't think this is actually used in this function.

Thanks, I guess that is the by-product of some refactoring.
I'll remove it.

> Pravin, do you have any further comments?
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