netdev - Re: [PATCH 1/2] igb: Allow extra 4 bytes on RX for vlan tags.

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Message-ID: <AANLkTinsWRAJ2bepa1NjQ4f0Wz46DaxWO6f_nEbmBAB0@mail.gmail.com>
Date:	Thu, 17 Feb 2011 03:04:32 -0800
From:	Jeff Kirsher <jeffrey.t.kirsher@...el.com>
To:	greearb@...delatech.com
Cc:	netdev@...r.kernel.org
Subject: Re: [PATCH 1/2] igb: Allow extra 4 bytes on RX for vlan tags.

On Thu, Feb 10, 2011 at 13:59,  <greearb@...delatech.com> wrote:
> From: Ben Greear <greearb@...delatech.com>
>
> This allows the NIC to receive 1518 byte (not counting
> FCS) packets when MTU is 1500, thus allowing 1500 MTU
> VLAN frames to be received.  Please note that no VLANs
> were actually configured on the NIC...it was just acting
> as pass-through device.
>
> Signed-off-by: Ben Greear <greearb@...delatech.com>
> ---
> :100644 100644 58c665b... 30c9cc6... M  drivers/net/igb/igb_main.c
>  drivers/net/igb/igb_main.c |    5 +++--
>  1 files changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/net/igb/igb_main.c b/drivers/net/igb/igb_main.c
> index 58c665b..30c9cc6 100644
> --- a/drivers/net/igb/igb_main.c
> +++ b/drivers/net/igb/igb_main.c
> @@ -2281,7 +2281,8 @@ static int __devinit igb_sw_init(struct igb_adapter *adapter)
>        adapter->rx_itr_setting = IGB_DEFAULT_ITR;
>        adapter->tx_itr_setting = IGB_DEFAULT_ITR;
>
> -       adapter->max_frame_size = netdev->mtu + ETH_HLEN + ETH_FCS_LEN;
> +       adapter->max_frame_size = (netdev->mtu + ETH_HLEN + ETH_FCS_LEN
> +                                  + VLAN_HLEN);
>        adapter->min_frame_size = ETH_ZLEN + ETH_FCS_LEN;
>
>        spin_lock_init(&adapter->stats64_lock);
> @@ -4303,7 +4304,7 @@ static int igb_change_mtu(struct net_device *netdev, int new_mtu)
>  {
>        struct igb_adapter *adapter = netdev_priv(netdev);
>        struct pci_dev *pdev = adapter->pdev;
> -       int max_frame = new_mtu + ETH_HLEN + ETH_FCS_LEN;
> +       int max_frame = new_mtu + ETH_HLEN + ETH_FCS_LEN + VLAN_HLEN;
>        u32 rx_buffer_len, i;
>
>        if ((new_mtu < 68) || (max_frame > MAX_JUMBO_FRAME_SIZE)) {

While testing this patch, validation found that the patch reduces the
maximum mtu size
by 4 bytes (reduces it from 9216 to 9212).  This is not a desired side
effect of this patch.

Thoughts?

-- 
Cheers,
Jeff
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