Re: [dpdk-dev] [PATCH v3 2/4] ethdev: move error checking macros to header

[Bruce Richardson <bruce.richardson@intel.com>]

On Wed, Nov 04, 2015 at 11:24:18AM +0100, Adrien Mazarguil wrote:
> On Wed, Nov 04, 2015 at 02:19:36AM +0100, Thomas Monjalon wrote:
> > 2015-11-03 12:00, Bruce Richardson:
> > > Move the function ptr and port id checking macros to the header file, so
> > > that they can be used in the static inline functions there. In doxygen
> > > comments, mark them as for internal use only.
> > [...]
> > > +/**
> > > + * @internal
> > > + *  Macro to print a message if in debugging mode
> > > + */
> > > +#ifdef RTE_LIBRTE_ETHDEV_DEBUG
> > > +#define RTE_PMD_DEBUG_TRACE(fmt, args...) \
> > > +		RTE_LOG(ERR, PMD, "%s: " fmt, __func__, ## args)
> > > +#else
> > > +#define RTE_PMD_DEBUG_TRACE(fmt, args...)
> > > +#endif
> > 
> > It does not compile because Mellanox drivers are pedantic:
> > 
> > In file included from /home/thomas/projects/dpdk/dpdk/drivers/net/mlx4/mlx4.c:78:0:
> > /home/thomas/projects/dpdk/dpdk/x86_64-native-linuxapp-gcc-shared-next/include/rte_ethdev.h: At top level:
> > /home/thomas/projects/dpdk/dpdk/x86_64-native-linuxapp-gcc-shared-next/include/rte_ethdev.h:933:38: error: ISO C does not permit named variadic macros [-Werror=variadic-macros]
> >  #define RTE_PMD_DEBUG_TRACE(fmt, args...) \
> 
> I suggest something like the following definitions as a pedantic-proof and
> standard compliant method (one drawback being that it cannot be done with a
> single macro), see PMD_DRV_LOG() in drivers/net/mlx5/mlx5_utils.h which also
> automatically appends a line feed:
> 
>  #ifdef RTE_LIBRTE_ETHDEV_DEBUG
> 
>  #define STRIP(a, b) a
>  #define OPAREN (
>  #define CPAREN )
>  #define COMMA ,
> 
>  #define RTE_PMD_DEBUG_TRACE(...) \
>          RTE_PMD_DEBUG_TRACE_(__VA_ARGS__ STRIP OPAREN, CPAREN)
> 
>  #define RTE_PMD_DEBUG_TRACE_(fmt, ...) \
>          RTE_PMD_DEBUG_TRACE__(fmt COMMA __func__, __VA_ARGS__)
> 
>  #define RTE_PMD_DEBUG_TRACE__(...) \
>          RTE_LOG(ERR, PMD, "%s: " __VA_ARGS__)
> 
>  #else /* RTE_LIBRTE_ETHDEV_DEBUG */
> 
>  #define RTE_PMD_DEBUG_TRACE(...)
> 
>  #endif /* RTE_LIBRTE_ETHDEV_DEBUG */
> 
> STRIP() and other helper macros are used to manage the dangling comma issue
> when __VA_ARGS__ is empty as in the first call below:
> 
>  RTE_PMD_DEBUG_TRACE("foo\n");
>  RTE_PMD_DEBUG_TRACE("foo %u\n", 42);
> 
> -- 
> Adrien Mazarguil
> 6WIND

Is this really the best way around this? It looks like a lot more complicated
than the original solution. Do we really need to support the -pedantic flag
in our header files?

/Bruce