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 11:19 PM, Alexander Lobakin wrote:
> External email: Use caution opening links or attachments
>
>
> From: Gavin Li <gavinl@nvidia.com>
> Date: Thu, 16 Feb 2023 16:40:33 +0800
>
>> On 2/16/2023 1:01 AM, Alexander Lobakin wrote:
>>> External email: Use caution opening links or attachments
>>>
>>>
>>> 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:
>>>>> External email: Use caution opening links or attachments
>>>>>
>>>>>
>>>>> 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?
> You wouldn't need to W/A it each time in each driver, just do it once in
> the inline itself.
> I did it once in __skb_header_pointer()[0] to be able to pass data
> pointer as const to optimize code a bit and point out explicitly that
> the function doesn't modify the packet anyhow, don't see any reason to
> not do the same here.
> Or, as I said, you can use macros + __builtin_choose_expr() or _Generic.
> container_of_const() uses the latter[1]. A __builtin_choose_expr()
> variant could rely on the __same_type() macro to check whether the
> pointer passed from the driver const or not.
ACK
>
>>>>>>> +     }
>>>>>>> +
>>>>>>> +     return 0;
>>>>>>> +}
>>> [...]
>>>
>>> Thanks,
>>> Olek
> [0]
> https://elixir.bootlin.com/linux/v6.2-rc8/source/include/linux/skbuff.h#L3992
> [1]
> https://elixir.bootlin.com/linux/v6.2-rc8/source/include/linux/container_of.h#L33
>
> Thanks,
> Olek