netdev - RE: [net-next 06/14] i40e: clamp jumbo frame size

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Date:	Thu, 5 Jun 2014 08:17:34 +0000
From:	David Laight <David.Laight@...LAB.COM>
To:	'Jeff Kirsher' <jeffrey.t.kirsher@...el.com>,
	"davem@...emloft.net" <davem@...emloft.net>
CC:	Jesse Brandeburg <jesse.brandeburg@...el.com>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"gospo@...hat.com" <gospo@...hat.com>,
	"sassmann@...hat.com" <sassmann@...hat.com>
Subject: RE: [net-next 06/14] i40e: clamp jumbo frame size

From: Jeff Kirsher
> From: Jesse Brandeburg <jesse.brandeburg@...el.com>
> 
> The driver was allowing the user to set larger size MTU
> than the hardware was being configured to support.
> 
> The driver was already using VLAN_HLEN when setting the
> hardware max receivable frame size, so just add it to the
> netdev MTU set entry point as well.
...
> --- a/drivers/net/ethernet/intel/i40e/i40e_main.c
> +++ b/drivers/net/ethernet/intel/i40e/i40e_main.c
> @@ -1698,7 +1698,7 @@ static void i40e_sync_filters_subtask(struct i40e_pf *pf)
>  static int i40e_change_mtu(struct net_device *netdev, int new_mtu)
>  {
>  	struct i40e_netdev_priv *np = netdev_priv(netdev);
> -	int max_frame = new_mtu + ETH_HLEN + ETH_FCS_LEN;
> +	int max_frame = new_mtu + ETH_HLEN + ETH_FCS_LEN + VLAN_HLEN;

Personally I'd write that sum as:
	int max_frame = ETH_HLEN + VLAN_HLEN + new_mtu + ETH_FCS_LEN;
so that the lengths are in the order the fields appear in the frame.

	David



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