netdev - Re: [PATCH 3/3] offloading: Force software GSO for multiple vlan tags.

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Date:	Fri, 7 Jan 2011 20:36:36 +0100
From:	Michał Mirosław <mirqus@...il.com>
To:	Jesse Gross <jesse@...ira.com>
Cc:	David Miller <davem@...emloft.net>, netdev@...r.kernel.org,
	Ben Hutchings <bhutchings@...arflare.com>
Subject: Re: [PATCH 3/3] offloading: Force software GSO for multiple vlan tags.

Hi,

Sorry for late reply, I noticed this patch only after it went to Linus' tree.

2010/10/30 Jesse Gross <jesse@...ira.com>:
> We currently use vlan_features to check for TSO support if there is
> a vlan tag.  However, it's quite likely that the NIC is not able to
> do TSO when there is an arbitrary number of tags.  Therefore if there
> is more than one tag (in-band or out-of-band), fall back to software
> emulation.
>
> Signed-off-by: Jesse Gross <jesse@...ira.com>
> CC: Ben Hutchings <bhutchings@...arflare.com>
> ---
>  include/linux/netdevice.h |    7 +++----
>  net/core/dev.c            |   16 ++++++++++++++++
>  2 files changed, 19 insertions(+), 4 deletions(-)
>
> diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
> index 072652d..980c752 100644
> --- a/include/linux/netdevice.h
> +++ b/include/linux/netdevice.h
> @@ -2234,6 +2234,8 @@ unsigned long netdev_fix_features(unsigned long features, const char *name);
>  void netif_stacked_transfer_operstate(const struct net_device *rootdev,
>                                        struct net_device *dev);
>
> +int netif_get_vlan_features(struct sk_buff *skb, struct net_device *dev);
> +
>  static inline int net_gso_ok(int features, int gso_type)
>  {
>        int feature = gso_type << NETIF_F_GSO_SHIFT;
> @@ -2249,10 +2251,7 @@ static inline int skb_gso_ok(struct sk_buff *skb, int features)
>  static inline int netif_needs_gso(struct net_device *dev, struct sk_buff *skb)
>  {
>        if (skb_is_gso(skb)) {
> -               int features = dev->features;
> -
> -               if (skb->protocol == htons(ETH_P_8021Q) || skb->vlan_tci)
> -                       features &= dev->vlan_features;
> +               int features = netif_get_vlan_features(skb, dev);
>
>                return (!skb_gso_ok(skb, features) ||
>                        unlikely(skb->ip_summed != CHECKSUM_PARTIAL));
> diff --git a/net/core/dev.c b/net/core/dev.c
> index 8bdda70..8d74988 100644
> --- a/net/core/dev.c
> +++ b/net/core/dev.c
> @@ -1969,6 +1969,22 @@ static inline void skb_orphan_try(struct sk_buff *skb)
>        }
>  }
>
> +int netif_get_vlan_features(struct sk_buff *skb, struct net_device *dev)
> +{
> +       __be16 protocol = skb->protocol;
> +
> +       if (protocol == htons(ETH_P_8021Q)) {
> +               struct vlan_ethhdr *veh = (struct vlan_ethhdr *)skb->data;
> +               protocol = veh->h_vlan_encapsulated_proto;
> +       } else if (!skb->vlan_tci)
> +               return dev->features;
> +
> +       if (protocol != htons(ETH_P_8021Q))
> +               return dev->features & dev->vlan_features;
> +       else
> +               return 0;
> +}

This clears all features for multiply-tagged frames. At least SG,
FRAGLIST and HW_CSUM are perfectly valid for those frames.

This doesn't really matter if this function stays used only in
netif_needs_gso(). It's name and placement suggests otherwise, though.

Best Regards,
Michał Mirosław
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