Re: [PATCH net-next v1 3/3] net/mlx5e: TC, Add support for VxLAN GBP encap/decap flows offload

[Gavin Li <gavinl@nvidia.com>]

On 2/16/2023 1:01 AM, Alexander Lobakin wrote:
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>
> From: Gavin Li <gavinl@nvidia.com>
> Date: Wed, 15 Feb 2023 16:30:04 +0800
>
>> On 2/15/2023 11:36 AM, Gavin Li wrote:
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>>>
>>>
>>> On 2/14/2023 11:26 PM, Alexander Lobakin wrote:
>>>> External email: Use caution opening links or attachments
>>>>
>>>>
>>>> From: Gavin Li <gavinl@nvidia.com>
>>>> Date: Tue, 14 Feb 2023 15:41:37 +0200
> [...]
>
>>>>> @@ -96,6 +99,70 @@ static int mlx5e_gen_ip_tunnel_header_vxlan(char
>>>>> buf[],
>>>>>         udp->dest = tun_key->tp_dst;
>>>>>         vxh->vx_flags = VXLAN_HF_VNI;
>>>>>         vxh->vx_vni = vxlan_vni_field(tun_id);
>>>>> +     if (tun_key->tun_flags & TUNNEL_VXLAN_OPT) {
>>>>> +             md = ip_tunnel_info_opts((struct ip_tunnel_info
>>>>> *)e->tun_info);
>>>>> +             vxlan_build_gbp_hdr(vxh, tun_key->tun_flags,
>>>>> +                                 (struct vxlan_metadata *)md);
>>>> Maybe constify both ip_tunnel_info_opts() and vxlan_build_gbp_hdr()
>>>> arguments instead of working around by casting away?
>>> ACK. Sorry for the confusion---I misunderstood the comment.
>> This ip_tunnel_info_opts is tricky to use const to annotate the arg
>> because it will have to cast from const to non-const again upon returning.
> It's okay to cast away for the `void *` returned.
> Alternatively, use can convert it to a macro and use
> __builtin_choose_expr() or _Generic to return const or non-const
> depending on whether the argument is constant. That's what was recently
> done for container_of() IIRC.

I've fixed vxlan_build_gbp_hdr in V2. For ip_tunnel_info_opts, it's 
confusing to me.

It would be as below after constifying the parameter.

static inline void *ip_tunnel_info_opts(const struct ip_tunnel_info *info)
{
     return (void *)(info + 1);
}
Is there any value gained by this change?

>
>>>>> +     }
>>>>> +
>>>>> +     return 0;
>>>>> +}
> [...]
>
> Thanks,
> Olek