From: Jim Baxter <jim_baxter@mentor•com>
To: Ben Hutchings <bhutchings@solarflare•com>
Cc: <netdev@vger•kernel.org>
Subject: Re: VLAN driver question
Date: Wed, 19 Jun 2013 16:57:11 +0100 [thread overview]
Message-ID: <51C1D4D7.1000904@mentor.com> (raw)
In-Reply-To: <1371566484.1956.16.camel@bwh-desktop.uk.level5networks.com>
Thank you Ben, that is very helpful.
On 18/06/13 15:41, Ben Hutchings wrote:
> On Mon, 2013-06-17 at 20:12 +0100, Jim Baxter wrote:
>> I have a network card that has a single flag to indicate if a received
>> packet contains a vlan packet.
>>
>> Can I use this to accelerate the kernels handling of the packet with
>> something like the following?
>>
>> /* Handle received VLAN packets */
>> if ((ndev->features & NETIF_F_HW_VLAN_CTAG_RX) && ebdp &&
>> (ebdp->cbd_esc &
>> BD_ENET_RX_VLAN)) {
>> /* Push and remove the vlan tag */
>> struct vlan_hdr *vlan_header;
>> u16 vlan_tag;
>> vlan_header = (struct vlan_hdr *) skb->data;
>> vlan_tag = ntohs(vlan_header->h_vlan_TCI);
>> __vlan_hwaccel_put_tag(skb, vlan_tag);
>> skb->len -= VLAN_HLEN;
>> skb->data += VLAN_HLEN;
>> vlan_set_encap_proto(skb, vlan_header);
>
> You have to move the Ethernet addresses forward as well. Imagine this
> device is being bridged - the Ethernet header won't be regenerated, so
> it has to be immediately before the network header.
>
Unless I have misunderstood, the Ethernet header is already copied
across to the skb by the Driver I am editing with the lines:
skb_reserve(skb, NET_IP_ALIGN);
skb_put(skb, pkt_len - 4); /* Make room */
skb_copy_to_linear_data(skb, data, pkt_len - 4);
skb->protocol = eth_type_trans(skb, ndev);
Thinking about it though I should actually use the flag from the driver
to create an skb of the size (pkt_len - 4 - VLAN_HLEN) and extract the
vlan header from data so it is not copied to the skb, does this sound
sensible?
>> }
>>
>> napi_gro_receive(&fep->napi, skb);
>
> I've been meaning to add a core function to do
> pull-out-VLAN-tag-and-GRO, although I'm more interested in
> napi_gro_frags(). Perhaps you could add the generic wrapper for
> napi_gro_receive()?
>
>> Also I cannot find any documentation stating what the difference is
>> between NETIF_F_HW_VLAN_CTAG_RX and NETIF_F_HW_VLAN_CTAG_FILTER, can
>> anyone define it?
>> The FILTER word on NETIF_F_HW_VLAN_CTAG_FILTER suggests it may be
>> applicable to received packets.
>
> NETIF_F_HW_VLAN_CTAG_RX means the device will extract VLAN tags so they
> aren't received inline.
>
> NETIF_F_HW_VLAN_CTAG_FILTER means the device can filter by VID. The
> driver's ndo_vlan_rx_{add,kill}_vid operations will be called to update
> the filter.
>
> Ben.
>
Jim
next prev parent reply other threads:[~2013-06-19 15:57 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-06-17 19:12 VLAN driver question Jim Baxter
2013-06-18 14:41 ` Ben Hutchings
2013-06-19 15:57 ` Jim Baxter [this message]
2013-06-19 16:33 ` Ben Hutchings
2013-06-20 19:05 ` Jim Baxter
2013-06-21 15:42 ` Ben Hutchings
2013-06-21 17:02 ` Jim Baxter
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