netdev - Re: [PATCH net 1/1] uapi: fix big endian definition of ipv6_rpl_sr

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Date:   Mon, 25 Jan 2021 13:12:42 -0700
From:   David Ahern <dsahern@...il.com>
To:     Jakub Kicinski <kuba@...nel.org>
Cc:     Justin Iurman <justin.iurman@...ege.be>, netdev@...r.kernel.org,
        davem@...emloft.net, alex aring <alex.aring@...il.com>
Subject: Re: [PATCH net 1/1] uapi: fix big endian definition of
 ipv6_rpl_sr_hdr

On 1/25/21 12:32 PM, Jakub Kicinski wrote:
>>>>> diff --git a/include/uapi/linux/rpl.h b/include/uapi/linux/rpl.h
>>>>> index 1dccb55cf8c6..708adddf9f13 100644
>>>>> --- a/include/uapi/linux/rpl.h
>>>>> +++ b/include/uapi/linux/rpl.h
>>>>> @@ -28,10 +28,10 @@ struct ipv6_rpl_sr_hdr {
>>>>>  		pad:4,
>>>>>  		reserved1:16;
>>>>>  #elif defined(__BIG_ENDIAN_BITFIELD)
>>>>> -	__u32	reserved:20,
>>>>> +	__u32	cmpri:4,
>>>>> +		cmpre:4,
>>>>>  		pad:4,
>>>>> -		cmpri:4,
>>>>> -		cmpre:4;
>>>>> +		reserved:20;
>>>>>  #else
>>>>>  #error  "Please fix <asm/byteorder.h>"
>>>>>  #endif  
>>
>> cross-checking with other headers - tcp and vxlan-gpe - this patch looks
>> correct.
> 
> What are you cross-checking?
> 

https://tools.ietf.org/html/draft-ietf-nvo3-vxlan-gpe-10, Section 3.1
header definition and vxlanhdr_gpe in include/net/vxlan.h. The
__BIG_ENDIAN_BITFIELD part follows the definition in the spec.

Similarly for the TCP header - RFC header definition and tcphdr in
include/uapi/linux/tcp.h. TCP header shows doff + res1 order which is
comparable to cmpri + cpmre in this header as both sets are 4-bits and
start a word.