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

[Adrien Mazarguil <adrien.mazarguil@6wind.com>]

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