netdev - Re: [RFC][net-next-2.6 PATCH v2] 8021q: set hard_header_len when VLAN offload features are toggled

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Message-ID: <AANLkTimTc2QwgsXk8qeU7ZBu977nOFLGQTx9sE5f4f-L@mail.gmail.com>
Date:	Wed, 27 Oct 2010 16:04:11 -0700
From:	Jesse Gross <jesse@...ira.com>
To:	John Fastabend <john.r.fastabend@...el.com>
Cc:	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"bhutchings@...arflare.com" <bhutchings@...arflare.com>
Subject: Re: [RFC][net-next-2.6 PATCH v2] 8021q: set hard_header_len when VLAN
 offload features are toggled

On Wed, Oct 27, 2010 at 2:40 PM, John Fastabend
<john.r.fastabend@...el.com> wrote:
> On 10/26/2010 7:05 PM, Jesse Gross wrote:
>> On Tue, Oct 26, 2010 at 2:59 PM, John Fastabend
>> <john.r.fastabend@...el.com> wrote:
>>> Toggling the vlan tx|rx hw offloads needs to set the hard_header_len
>>> as well otherwise we end up using LL_RESERVED_SPACE incorrectly.
>>> This results in pskb_expand_head() being used unnecessarily.
>>>
>>> This add a check in vlan_transfer_features  to catch the ETH_FLAG_TXVLAN
>>> flag and set the header length. This requires drivers to add the
>>> ETH_FLAG_TXVLAN to vlan_features.
>>>
>>> Signed-off-by: John Fastabend <john.r.fastabend@...el.com>
>>
>> I think this addresses all of the original problems.  However, I don't
>> think that we want to have drivers claim to support vlan offloading as
>> a feature for vlan packets.  That implies some type of QinQ
>> functionality to me.  In addition, if the vlan device claims to
>> support offloading and a second vlan device is stacked on top of it,
>> then the two will clobber skb->vlan_tci.  It's probably simpler to
>> just keep track of whether vlan offloading is currently enabled so we
>> can find out whether it changed.
>>
>
> Agreed. Rather then trying to be clever this is probably the easiest.
>
> --- a/net/8021q/vlan.c
> +++ b/net/8021q/vlan.c
> @@ -334,6 +334,12 @@ Hunk #1, a/net/8021q/vlan.c static void vlan_transfer_features(struct net_device *dev,
>        vlandev->features &= ~dev->vlan_features;
>        vlandev->features |= dev->features & dev->vlan_features;
>        vlandev->gso_max_size = dev->gso_max_size;
> +
> +       if (dev->features & NETIF_F_HW_VLAN_TX)
> +               vlandev->hard_header_len = dev->hard_header_len;
> +       else
> +               vlandev->hard_header_len = dev->hard_header_len + VLAN_HLEN;
> +

Great, that's even simpler than I was thinking.

I think this series is ready to go.
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