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

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Message-ID: <513e8605-2687-132b-f967-4c33538adc34@huawei.com>
Date:   Thu, 9 Jul 2020 10:55:27 +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 2020/7/9 10:47, Eric Dumazet wrote:
> 
> 
> On 7/8/20 7:30 PM, tanhuazhong wrote:
>>
>>
>> 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?
> 
> This could be done in an ndo_fix_features(), or ndo_features_check()
> 
> Or maybe we do not care, but this should probably be documented.
> 

Thanks for your suggestion.
If only check NETIF_F_HW_CSUM here is more acceptable?

> 
>