netdev - Re: [PATCH V2 net-next 4/6] tun: Add support for SCTP checksum offload

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Date:   Wed, 2 May 2018 13:17:50 -0400
From:   Vlad Yasevich <vyasevic@...hat.com>
To:     Marcelo Ricardo Leitner <marcelo.leitner@...il.com>,
        Vladislav Yasevich <vyasevich@...il.com>
Cc:     netdev@...r.kernel.org, linux-sctp@...r.kernel.org,
        virtualization@...ts.linux-foundation.org,
        virtio-dev@...ts.oasis-open.org, mst@...hat.com,
        jasowang@...hat.com, nhorman@...driver.com
Subject: Re: [PATCH V2 net-next 4/6] tun: Add support for SCTP checksum
 offload

On 05/02/2018 10:56 AM, Marcelo Ricardo Leitner wrote:
> On Wed, May 02, 2018 at 11:53:47AM -0300, Marcelo Ricardo Leitner wrote:
>> On Tue, May 01, 2018 at 10:07:37PM -0400, Vladislav Yasevich wrote:
>>> Adds a new tun offload flag to allow for SCTP checksum offload.
>>> The flag has to be set by the user and defaults to "no offload".
>>
>> I'm confused here:
>>
>>> +++ b/drivers/net/tun.c
>>> @@ -216,7 +216,7 @@ struct tun_struct {
>>>  	struct net_device	*dev;
>>>  	netdev_features_t	set_features;
>>>  #define TUN_USER_FEATURES (NETIF_F_HW_CSUM|NETIF_F_TSO_ECN|NETIF_F_TSO| \
>>> -			  NETIF_F_TSO6)
>>> +			  NETIF_F_TSO6|NETIF_F_SCTP_CRC)
>>
>> Doesn't adding it here mean it defaults to "offload", instead?
>>
>> later on, it does:
>>                 dev->hw_features = NETIF_F_SG | NETIF_F_FRAGLIST |
>>                                    TUN_USER_FEATURES | NETIF_F_HW_VLAN_CTAG_TX |
>>                                    NETIF_F_HW_VLAN_STAG_TX;
> 
> Missed to paste the next line too:
>                 dev->features = dev->hw_features | NETIF_F_LLTX;
> 

Yes, as a software device, we can default it to on.  However, qemu will 0-out
the features and then set them up based on the guest (just like regular checksum).

-vlad