Re: [PATCH] samples: bpf: xdp1: remove duplicate code to find protocol

[Yonghong Song <yhs@fb.com>]

On 8/8/21 10:19 AM, Muhammad Falak Reyaz wrote:
> On Sun, Aug 8, 2021 at 10:23 PM Yonghong Song <yhs@fb.com> wrote:
>>
>>
>>
>> On 8/8/21 5:24 AM, Muhammad Falak R Wani wrote:
>>> The code to find h_vlan_encapsulated_proto is duplicated.
>>> Remove the extra block.
>>>
>>> Signed-off-by: Muhammad Falak R Wani <falakreyaz@gmail.com>
>>> ---
>>>    samples/bpf/xdp1_kern.c | 9 ---------
>>>    1 file changed, 9 deletions(-)
>>>
>>> diff --git a/samples/bpf/xdp1_kern.c b/samples/bpf/xdp1_kern.c
>>> index 34b64394ed9c..a35e064d7726 100644
>>> --- a/samples/bpf/xdp1_kern.c
>>> +++ b/samples/bpf/xdp1_kern.c
>>> @@ -57,15 +57,6 @@ int xdp_prog1(struct xdp_md *ctx)
>>>
>>>        h_proto = eth->h_proto;
>>>
>>> -     if (h_proto == htons(ETH_P_8021Q) || h_proto == htons(ETH_P_8021AD)) {
>>> -             struct vlan_hdr *vhdr;
>>> -
>>> -             vhdr = data + nh_off;
>>> -             nh_off += sizeof(struct vlan_hdr);
>>> -             if (data + nh_off > data_end)
>>> -                     return rc;
>>> -             h_proto = vhdr->h_vlan_encapsulated_proto;
>>
>> No. This is not a duplicate. The h_proto in the above line will be used
>> in the below "if" condition.
>>
>>> -     }
>>>        if (h_proto == htons(ETH_P_8021Q) || h_proto == htons(ETH_P_8021AD)) {
>>>                struct vlan_hdr *vhdr;
>>>
>>>
> Apologies :(
> I now realize, it could be double vlan encapsulated.
> Would it make sense to add an explicit comment for newbies like me ?
> I can send a patch, if it is okay.

This is not the first time people sending a patch trying to remove this
"duplicated" code. I think it is okay to send a patch with comments to 
say this is intended to handle nested vlan, so we can save everybody's 
time. Thanks.

> 
> -mfrw
>