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Date:	Fri, 21 Nov 2014 10:41:27 -0800
From:	Pravin Shelar <pshelar@...ira.com>
To:	Jiri Pirko <jiri@...nulli.us>, Jiri Benc <jbenc@...hat.com>
Cc:	netdev <netdev@...r.kernel.org>,
	David Miller <davem@...emloft.net>,
	Jamal Hadi Salim <jhs@...atatu.com>,
	Tom Herbert <therbert@...gle.com>,
	Eric Dumazet <edumazet@...gle.com>,
	Willem de Bruijn <willemb@...gle.com>,
	Daniel Borkmann <dborkman@...hat.com>, mst@...hat.com,
	fw@...len.de, Paul.Durrant@...rix.com, Thomas Graf <tgraf@...g.ch>,
	Cong Wang <cwang@...pensource.com>
Subject: Re: [patch net-next v4 8/9] net: move vlan pop/push functions into
 common code

On Fri, Nov 21, 2014 at 10:05 AM, Jiri Pirko <jiri@...nulli.us> wrote:
> Fri, Nov 21, 2014 at 05:11:39PM CET, pshelar@...ira.com wrote:
>>On Wed, Nov 19, 2014 at 5:05 AM, Jiri Pirko <jiri@...nulli.us> wrote:
>>> So it can be used from out of openvswitch code.
>>> Did couple of cosmetic changes on the way, namely variable naming and
>>> adding support for 8021AD proto.
>>>
>>> Signed-off-by: Jiri Pirko <jiri@...nulli.us>
>>> ---
>>>
>>> v3->v4:
>>> - don't try to be smart and copy skb->mac_len manipulation as it is. It can be
>>>   adjusted later on.
>>
>>I am fine with moving this code to generic library, as long as we can
>>adjust the mac_len as offset for MPLS header, otherwise this breaks
>>MPLS support.
>
> Pravin, I'm just moving the code without changing it in this aspect.
> Maybe I'm missing something but can you tell me what you see wrong?
> Thanks.
>

There is bug in the openvswitch code where vlan-pop does mac-length
reset rather than subtracting VLAN_HLEN  from mac-len. MPLS code
depends on this. Now this patch moves the bug to common code. I am
fine with this patch and I can send fix to change code vlan-pop code
to adjust mac_len later on.
But I am worried about the comment made by Jiri Benc on earlier
version of this patch where is mentioned that subtracting VLAN_HLEN
can break common case for vlan-pop. In that case we can not change
this common function. Jiri Benc, Can you point me to the code, so the
we can work on solution to fix this issue.

>>
>>> - fix error path in do_execute_actions as suggested by Pravin
>>> v2->v3:
>>> - used previously introduced __vlan_insert_tag helper
>>> - used skb_push/pull to get skb->data into needed point
>>> - fixed skb->mac_len computation in skb_vlan_push pointed out by Pravin
>>> v1->v2:
>>> - adjusted to fix recent ovs changes
>>> - included change to use make_writable suggested by Eric
>>>
>>>  include/linux/skbuff.h    |  2 +
>>>  net/core/skbuff.c         | 95 +++++++++++++++++++++++++++++++++++++++++++++++
>>>  net/openvswitch/actions.c | 86 +++++-------------------------------------
>>>  3 files changed, 106 insertions(+), 77 deletions(-)
>>>
>>> diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
>>> index e045516..78c299f 100644
>>> --- a/include/linux/skbuff.h
>>> +++ b/include/linux/skbuff.h
>>> @@ -2679,6 +2679,8 @@ unsigned int skb_gso_transport_seglen(const struct sk_buff *skb);
>>>  struct sk_buff *skb_segment(struct sk_buff *skb, netdev_features_t features);
>>>  struct sk_buff *skb_vlan_untag(struct sk_buff *skb);
>>>  int skb_ensure_writable(struct sk_buff *skb, int write_len);
>>> +int skb_vlan_pop(struct sk_buff *skb);
>>> +int skb_vlan_push(struct sk_buff *skb, __be16 vlan_proto, u16 vlan_tci);
>>>
>>>  struct skb_checksum_ops {
>>>         __wsum (*update)(const void *mem, int len, __wsum wsum);
>>> diff --git a/net/core/skbuff.c b/net/core/skbuff.c
>>> index d11bbe0..c906c5f 100644
>>> --- a/net/core/skbuff.c
>>> +++ b/net/core/skbuff.c
>>> @@ -4163,6 +4163,101 @@ int skb_ensure_writable(struct sk_buff *skb, int write_len)
>>>  }
>>>  EXPORT_SYMBOL(skb_ensure_writable);
>>>
>>> +/* remove VLAN header from packet and update csum accordingly. */
>>> +static int __skb_vlan_pop(struct sk_buff *skb, u16 *vlan_tci)
>>> +{
>>> +       struct vlan_hdr *vhdr;
>>> +       unsigned int offset = skb->data - skb_mac_header(skb);
>>> +       int err;
>>> +
>>> +       __skb_push(skb, offset);
>>> +       err = skb_ensure_writable(skb, VLAN_ETH_HLEN);
>>> +       if (unlikely(err))
>>> +               goto pull;
>>> +
>>> +       skb_postpull_rcsum(skb, skb->data + (2 * ETH_ALEN), VLAN_HLEN);
>>> +
>>> +       vhdr = (struct vlan_hdr *)(skb->data + ETH_HLEN);
>>> +       *vlan_tci = ntohs(vhdr->h_vlan_TCI);
>>> +
>>> +       memmove(skb->data + VLAN_HLEN, skb->data, 2 * ETH_ALEN);
>>> +       __skb_pull(skb, VLAN_HLEN);
>>> +
>>> +       vlan_set_encap_proto(skb, vhdr);
>>> +       skb->mac_header += VLAN_HLEN;
>>> +
>>> +       if (skb_network_offset(skb) < ETH_HLEN)
>>> +               skb_set_network_header(skb, ETH_HLEN);
>>> +
>>> +       skb_reset_mac_len(skb);
>>> +pull:
>>> +       __skb_pull(skb, offset);
>>> +
>>> +       return err;
>>> +}
>>> +
>>> +int skb_vlan_pop(struct sk_buff *skb)
>>> +{
>>> +       u16 vlan_tci;
>>> +       __be16 vlan_proto;
>>> +       int err;
>>> +
>>> +       if (likely(vlan_tx_tag_present(skb))) {
>>> +               skb->vlan_tci = 0;
>>> +       } else {
>>> +               if (unlikely((skb->protocol != htons(ETH_P_8021Q) &&
>>> +                             skb->protocol != htons(ETH_P_8021AD)) ||
>>> +                            skb->len < VLAN_ETH_HLEN))
>>> +                       return 0;
>>> +
>>> +               err = __skb_vlan_pop(skb, &vlan_tci);
>>> +               if (err)
>>> +                       return err;
>>> +       }
>>> +       /* move next vlan tag to hw accel tag */
>>> +       if (likely((skb->protocol != htons(ETH_P_8021Q) &&
>>> +                   skb->protocol != htons(ETH_P_8021AD)) ||
>>> +                  skb->len < VLAN_ETH_HLEN))
>>> +               return 0;
>>> +
>>> +       vlan_proto = skb->protocol;
>>> +       err = __skb_vlan_pop(skb, &vlan_tci);
>>> +       if (unlikely(err))
>>> +               return err;
>>> +
>>> +       __vlan_hwaccel_put_tag(skb, vlan_proto, vlan_tci);
>>> +       return 0;
>>> +}
>>> +EXPORT_SYMBOL(skb_vlan_pop);
>>> +
>>> +int skb_vlan_push(struct sk_buff *skb, __be16 vlan_proto, u16 vlan_tci)
>>> +{
>>> +       if (vlan_tx_tag_present(skb)) {
>>> +               unsigned int offset = skb->data - skb_mac_header(skb);
>>> +               int err;
>>> +
>>> +               /* __vlan_insert_tag expect skb->data pointing to mac header.
>>> +                * So change skb->data before calling it and change back to
>>> +                * original position later
>>> +                */
>>> +               __skb_push(skb, offset);
>>> +               err = __vlan_insert_tag(skb, skb->vlan_proto,
>>> +                                       vlan_tx_tag_get(skb));
>>> +               if (err)
>>> +                       return err;
>>> +               skb->protocol = skb->vlan_proto;
>>> +               skb->mac_len += VLAN_HLEN;
>>> +               __skb_pull(skb, offset);
>>> +
>>> +               if (skb->ip_summed == CHECKSUM_COMPLETE)
>>> +                       skb->csum = csum_add(skb->csum, csum_partial(skb->data
>>> +                                       + (2 * ETH_ALEN), VLAN_HLEN, 0));
>>> +       }
>>> +       __vlan_hwaccel_put_tag(skb, vlan_proto, vlan_tci);
>>> +       return 0;
>>> +}
>>> +EXPORT_SYMBOL(skb_vlan_push);
>>> +
>>>  /**
>>>   * alloc_skb_with_frags - allocate skb with page frags
>>>   *
>>> diff --git a/net/openvswitch/actions.c b/net/openvswitch/actions.c
>>> index 7ffa377..4e05ea1 100644
>>> --- a/net/openvswitch/actions.c
>>> +++ b/net/openvswitch/actions.c
>>> @@ -206,93 +206,27 @@ static int set_mpls(struct sk_buff *skb, struct sw_flow_key *key,
>>>         return 0;
>>>  }
>>>
>>> -/* remove VLAN header from packet and update csum accordingly. */
>>> -static int __pop_vlan_tci(struct sk_buff *skb, __be16 *current_tci)
>>> -{
>>> -       struct vlan_hdr *vhdr;
>>> -       int err;
>>> -
>>> -       err = skb_ensure_writable(skb, VLAN_ETH_HLEN);
>>> -       if (unlikely(err))
>>> -               return err;
>>> -
>>> -       skb_postpull_rcsum(skb, skb->data + (2 * ETH_ALEN), VLAN_HLEN);
>>> -
>>> -       vhdr = (struct vlan_hdr *)(skb->data + ETH_HLEN);
>>> -       *current_tci = vhdr->h_vlan_TCI;
>>> -
>>> -       memmove(skb->data + VLAN_HLEN, skb->data, 2 * ETH_ALEN);
>>> -       __skb_pull(skb, VLAN_HLEN);
>>> -
>>> -       vlan_set_encap_proto(skb, vhdr);
>>> -       skb->mac_header += VLAN_HLEN;
>>> -
>>> -       if (skb_network_offset(skb) < ETH_HLEN)
>>> -               skb_set_network_header(skb, ETH_HLEN);
>>> -
>>> -       /* Update mac_len for subsequent MPLS actions */
>>> -       skb_reset_mac_len(skb);
>>> -       return 0;
>>> -}
>>> -
>>>  static int pop_vlan(struct sk_buff *skb, struct sw_flow_key *key)
>>>  {
>>> -       __be16 tci;
>>>         int err;
>>>
>>> -       if (likely(vlan_tx_tag_present(skb))) {
>>> -               skb->vlan_tci = 0;
>>> -       } else {
>>> -               if (unlikely(skb->protocol != htons(ETH_P_8021Q) ||
>>> -                            skb->len < VLAN_ETH_HLEN))
>>> -                       return 0;
>>> -
>>> -               err = __pop_vlan_tci(skb, &tci);
>>> -               if (err)
>>> -                       return err;
>>> -       }
>>> -       /* move next vlan tag to hw accel tag */
>>> -       if (likely(skb->protocol != htons(ETH_P_8021Q) ||
>>> -                  skb->len < VLAN_ETH_HLEN)) {
>>> +       err = skb_vlan_pop(skb);
>>> +       if (vlan_tx_tag_present(skb))
>>> +               invalidate_flow_key(key);
>>> +       else
>>>                 key->eth.tci = 0;
>>> -               return 0;
>>> -       }
>>> -
>>> -       invalidate_flow_key(key);
>>> -       err = __pop_vlan_tci(skb, &tci);
>>> -       if (unlikely(err))
>>> -               return err;
>>> -
>>> -       __vlan_hwaccel_put_tag(skb, htons(ETH_P_8021Q), ntohs(tci));
>>> -       return 0;
>>> +       return err;
>>>  }
>>>
>>>  static int push_vlan(struct sk_buff *skb, struct sw_flow_key *key,
>>>                      const struct ovs_action_push_vlan *vlan)
>>>  {
>>> -       if (unlikely(vlan_tx_tag_present(skb))) {
>>> -               u16 current_tag;
>>> -
>>> -               /* push down current VLAN tag */
>>> -               current_tag = vlan_tx_tag_get(skb);
>>> -
>>> -               skb = vlan_insert_tag_set_proto(skb, skb->vlan_proto,
>>> -                                               current_tag);
>>> -               if (!skb)
>>> -                       return -ENOMEM;
>>> -               /* Update mac_len for subsequent MPLS actions */
>>> -               skb->mac_len += VLAN_HLEN;
>>> -
>>> -               if (skb->ip_summed == CHECKSUM_COMPLETE)
>>> -                       skb->csum = csum_add(skb->csum, csum_partial(skb->data
>>> -                                       + (2 * ETH_ALEN), VLAN_HLEN, 0));
>>> -
>>> +       if (vlan_tx_tag_present(skb))
>>>                 invalidate_flow_key(key);
>>> -       } else {
>>> +       else
>>>                 key->eth.tci = vlan->vlan_tci;
>>> -       }
>>> -       __vlan_hwaccel_put_tag(skb, vlan->vlan_tpid, ntohs(vlan->vlan_tci) & ~VLAN_TAG_PRESENT);
>>> -       return 0;
>>> +       return skb_vlan_push(skb, vlan->vlan_tpid,
>>> +                            ntohs(vlan->vlan_tci) & ~VLAN_TAG_PRESENT);
>>>  }
>>>
>>>  static int set_eth_addr(struct sk_buff *skb, struct sw_flow_key *key,
>>> @@ -858,8 +792,6 @@ static int do_execute_actions(struct datapath *dp, struct sk_buff *skb,
>>>
>>>                 case OVS_ACTION_ATTR_PUSH_VLAN:
>>>                         err = push_vlan(skb, key, nla_data(a));
>>> -                       if (unlikely(err)) /* skb already freed. */
>>> -                               return err;
>>>                         break;
>>>
>>>                 case OVS_ACTION_ATTR_POP_VLAN:
>>> --
>>> 1.9.3
>>>
--
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