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

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Message-ID: <7529a39a-de9a-0ea9-152c-e1fca64be157@huawei.com>
Date:   Thu, 9 Jul 2020 10:30:35 +0800
From:   tanhuazhong <tanhuazhong@...wei.com>
To:     Eric Dumazet <eric.dumazet@...il.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 2020/7/8 13:36, Eric Dumazet wrote:
> 
> 
> 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 ?
> 

Yes, not like TCP (who uses NETIF_F_TSO for IPv4 and NETIF_F_TSO6 for IPv6),
UDP only has a NETIF_F_GSO_UDP_L4 for both IPv4 and IPv6.
I cannot find a better way to do it with combined IPv4 and IPv6 csum 
together.
For this issue, is there any good idea to fix it?

>> +		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;
>>
> 
>