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

[Dmitry Kozlyuk]

2021-05-20 17:04 (UTC+0100), 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?

Yes, only it's `S_un.S_addr`, sorry for the typo in my explanation.
Both code snippets from commit message 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.
> >   
>