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

[Dmitry Kozlyuk <dmitry.kozliuk@gmail.com>]

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.
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.