[dpdk-dev] [PATCH] doc: announce renaming of rte_ether_hdr fields

[Ferruh Yigit]

On 5/20/2021 4:50 PM, Dmitry Kozlyuk wrote:
> 2021-05-20 16:27 (UTC+0100), Ferruh Yigit:
>> On 5/20/2021 4:06 PM, Dmitry Kozlyuk wrote:
>>> 2021-05-20 15:24 (UTC+0100), Ferruh Yigit:  
>>>> On 3/3/2021 10:51 PM, Dmitry Kozlyuk wrote:  
>>> [...]  
>>>>>
>>>>> It is not mandatory to rename `d_addr`, this is for consistency only.
>>>>> Naming in `rte_ether_hdr` will also resemble `rte_ipv4/6_hdr`.
>>>>>
>>>>> Workaround is to define `struct rte_ether_hdr` in such a away that
>>>>> it can be used with or without `s_addr` macro (as defined on Windows)
>>>>> This can be done for Windows only or for all platforms to save space.
>>>>>
>>>>>     #pragma push_macro("s_addr")
>>>>>     #ifdef s_addr
>>>>>     #undef s_addr
>>>>>     #endif
>>>>>
>>>>>     struct rte_ether_hdr {
>>>>>         struct rte_ether_addr d_addr; /**< Destination address. */
>>>>>         RTE_STD_C11
>>>>>         union {
>>>>>             struct rte_ether_addr s_addr; /**< Source address. */
>>>>>             struct {
>>>>>                 struct rte_ether_addr S_un;
>>>>>                 /**< MUST NOT be used directly, only via s_addr */
>>>>>             } S_addr;
>>>>>             /*< MUST NOT be used directly, only via s_addr */
>>>>>         };
>>>>>         uint16_t ether_type; /**< Frame type. */
>>>>>     } __rte_aligned(2);
>>>>>
>>>>>     #pragma pop_macro("s_addr")
>>>>>     
>>>>
>>>> What is the problem with the workaround, why we can't live with it?
>>>>
>>>> It requires an order in include files, right?  
>>>
>>> There's no problem except a tricky structure definition with fields that
>>> violate DPDK coding rules. It works with any include order.
>>>
>>> Will fix typos in v3, thanks.
>>>   
>>
>> For following case, won't compiler take 's_addr' as macro?
>>
>>     #include <rte_ether.h>
>>     #include <winsock2.h>
>>     struct rte_ether_hdr eh;
>>     /* eh.s_addr.addr_bytes[0] = 0;
>>
> 
> Yes, it will. The macro will expand to `S_addr.S_un` and compile successfully.

will 'eh.S_addr.S_un.addr_bytes[0] = 0;' compile successfully?

> In theory, Microsoft can change the definition of `s_addr`, and while I doubt
> they will, it's a valid concern and a reason to remove workaround in 21.11.
>