netdev - Re: [RFC net-next 2/2] net: disable UDP GSO feature when CSUM is disabled

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Date:   Tue, 7 Jul 2020 22:36:57 -0700
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Huazhong Tan <tanhuazhong@...wei.com>, davem@...emloft.net,
        willemb@...gle.com
Cc:     netdev@...r.kernel.org, linuxarm@...wei.com, kuba@...nel.org
Subject: Re: [RFC net-next 2/2] net: disable UDP GSO feature when CSUM is
 disabled



On 7/7/20 8:48 PM, Huazhong Tan wrote:
> Since UDP GSO feature is depended on checksum offload, so disable
> UDP GSO feature when CSUM is disabled, then from user-space also
> can see UDP GSO feature is disabled.
> 
> Signed-off-by: Huazhong Tan <tanhuazhong@...wei.com>
> ---
>  net/core/dev.c | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/net/core/dev.c b/net/core/dev.c
> index c02bae9..dcb6b35 100644
> --- a/net/core/dev.c
> +++ b/net/core/dev.c
> @@ -9095,6 +9095,12 @@ static netdev_features_t netdev_fix_features(struct net_device *dev,
>  		features &= ~NETIF_F_TSO6;
>  	}
>  
> +	if ((features & NETIF_F_GSO_UDP_L4) && !(features & NETIF_F_HW_CSUM) &&
> +	    (!(features & NETIF_F_IP_CSUM) || !(features & NETIF_F_IPV6_CSUM))) {

This would prevent a device providing IPv4 checksum only (no IPv6 csum support) from sending IPv4 UDP GSO packets ?

> +		netdev_dbg(dev, "Dropping UDP GSO features since no CSUM feature.\n");
> +		features &= ~NETIF_F_GSO_UDP_L4;
> +	}
> +
>  	/* TSO with IPv4 ID mangling requires IPv4 TSO be enabled */
>  	if ((features & NETIF_F_TSO_MANGLEID) && !(features & NETIF_F_TSO))
>  		features &= ~NETIF_F_TSO_MANGLEID;
>