[dpdk-dev] [EXT] Re: [PATCH v4] doc: announce API changes for Windows compatibility

[Dmitry Kozlyuk]

2021-08-02 12:45 (UTC+0000), Akhil Goyal:
> > 21/07/2021 21:55, Dmitry Kozlyuk:  
> > > Windows headers define `s_addr`, `min`, and `max` as macros.
> > > If DPDK headers are included after Windows ones, DPDK structure
> > > definitions containing fields with these names get broken (example 1),
> > > as well as any usage of such fields (example 2). If DPDK headers
> > > undefined these macros, it could break consumer code (example 3).
> > > It is proposed to rename structure fields in DPDK, because Win32 headers
> > > are used more widely than DPDK, as a general-purpose platform compared
> > > to domain-specific kit, and are harder to fix because of that.
> > > Exact new names are left for further discussion.
> > >
> > > Example 1:
> > >
> > >     /* in DPDK public header included after windows.h */
> > >     struct rte_type {
> > >         int min;    /* ERROR: `min` is a macro */
> > >     };
> > >
> > > Example 2:
> > >
> > >     #include <rte_ether.h>
> > >     #include <winsock2.h>
> > >     struct rte_ether_hdr eh;
> > >     eh.s_addr.addr_bytes[0] = 0;    /* ERROR: `addr_s` is a macro */
> > >
> > > Example 3:
> > >
> > >     #include <winsock2.h>
> > >     #include <rte_ether.h>
> > >     struct in_addr addr;
> > >     addr.s_addr = 0;      /* ERROR: there is no `s_addr` field,
> > >                              and `s_addr` macro is undefined by DPDK. */
> > >
> > > Commit 6c068dbd9fea ("net: work around s_addr macro on Windows")
> > > modified definition of `struct rte_ether_hdr` to avoid the issue.
> > > However, the workaround assumes `#define s_addr S_addr.S_un`
> > > in Windows headers, which is not a part of official API.
> > > It also complicates the definition of `struct rte_ether_hdr`.
> > >
> > > Signed-off-by: Dmitry Kozlyuk <dmitry.kozliuk at gmail.com>
> > > Acked-by: Khoa To <khot at microsoft.com>
> > > ---
> > > +* net: ``s_addr`` and ``d_addr`` fields of ``rte_ether_hdr`` structure
> > > +  will be renamed in DPDK 21.11 to avoid conflict with Windows Sockets  
> > headers.  
> > > +
> > > +* compressdev: ``min`` and ``max`` fields of ``rte_param_log2_range``  
> > structure  
> > > +  will be renamed in DPDK 21.11 to avoid conflict with Windows Sockets  
> > headers.
> > 
> > The struct rte_param_log2_range should also be renamed to include
> > "compress" prefix.
> > But as we break the struct API, it is not an issue I guess.
> >   
> > > +* cryptodev: ``min`` and ``max`` fields of ``rte_crypto_param_range``  
> > structure  
> > > +  will be renamed in DPDK 21.11 to avoid conflict with Windows Sockets  
> > headers.
> > 
> > Acked-by: Thomas Monjalon <thomas at monjalon.net>
> >   
> Can we have a local variable named as min/max?
> If not, then I believe it is not a good idea.

Yes, except for inline functions in public headers.
The only problematic one I know of is this (rte_lru_x86.h):

static inline int
f_lru_pos(uint64_t lru_list)
{
	__m128i lst = _mm_set_epi64x((uint64_t)-1, lru_list);
	__m128i min = _mm_minpos_epu16(lst); /* <<< */
	return _mm_extract_epi16(min, 1);
}

Fixing it breaks neither API nor ABI, thus no explicit deprecation notice.