netdev - Re: [PATCH] xen-netfront, xen-netback: Use correct minimum MTU values

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Date:   Mon, 16 Oct 2017 16:43:34 +0200
From:   Eduardo Otubo <otubo@...hat.com>
To:     Mohammed Gamal <mgamal@...hat.com>
Cc:     netdev@...r.kernel.org, xen-devel@...ts.xenproject.org,
        paul.durrant@...rix.com, wei.liu2@...rix.com,
        linux-kernel@...r.kernel.org, vkuznets@...hat.com,
        cavery@...hat.com, cheshi@...hat.com
Subject: Re: [PATCH] xen-netfront, xen-netback: Use correct minimum MTU values

On Mon, Oct 16, 2017 at 03:20:32PM +0200, Mohammed Gamal wrote:
> RFC791 specifies the minimum MTU to be 68, while xen-net{front|back}
> drivers use a minimum value of 0.
> 
> When set MTU to 0~67 with xen_net{front|back} driver, the network
> will become unreachable immediately, the guest can no longer be pinged.
> 
> xen_net{front|back} should not allow the user to set this value which causes
> network problems.
> 
> Reported-by: Chen Shi <cheshi@...hat.com>
> Signed-off-by: Mohammed Gamal <mgamal@...hat.com>
> ---
>  drivers/net/xen-netback/interface.c | 2 +-
>  drivers/net/xen-netfront.c          | 2 +-
>  2 files changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/net/xen-netback/interface.c b/drivers/net/xen-netback/interface.c
> index ee8ed9da..4491ca5 100644
> --- a/drivers/net/xen-netback/interface.c
> +++ b/drivers/net/xen-netback/interface.c
> @@ -486,7 +486,7 @@ struct xenvif *xenvif_alloc(struct device *parent, domid_t domid,
>  
>  	dev->tx_queue_len = XENVIF_QUEUE_LENGTH;
>  
> -	dev->min_mtu = 0;
> +	dev->min_mtu = ETH_MIN_MTU;
>  	dev->max_mtu = ETH_MAX_MTU - VLAN_ETH_HLEN;
>  
>  	/*
> diff --git a/drivers/net/xen-netfront.c b/drivers/net/xen-netfront.c
> index 523387e..8b8689c 100644
> --- a/drivers/net/xen-netfront.c
> +++ b/drivers/net/xen-netfront.c
> @@ -1316,7 +1316,7 @@ static struct net_device *xennet_create_dev(struct xenbus_device *dev)
>  	netdev->features |= netdev->hw_features;
>  
>  	netdev->ethtool_ops = &xennet_ethtool_ops;
> -	netdev->min_mtu = 0;
> +	netdev->min_mtu = ETH_MIN_MTU;
>  	netdev->max_mtu = XEN_NETIF_MAX_TX_SIZE;
>  	SET_NETDEV_DEV(netdev, &dev->dev);
>  
> -- 
> 1.8.3.1
> 

Acked-by: Eduardo Otubo <otubo@...hat.com>

-- 
Eduardo Otubo
Senior Software Engineer @ RedHat