Re: [dpdk-dev] [PATCH] eal: simplify RTE_PMD_DEBUG_TRACE

[Jeff Shaw <jeffrey.b.shaw@intel.com>]

On Fri, Dec 14, 2018 at 12:50:55PM -0800, Stephen Hemminger wrote:
> Use rte_log directly, eliminating no longer used rte_pmd_dev_trace
> function. This removes variable length array which is problem on
> Windows and other compilers not doing C99.
> 
> Also, drop unused RTE_PROC_PRIMARY macros.
> 
> Reported-by: Jeff Shaw <jeffrey.b.shaw@intel.com>
> Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>
> ---
>  lib/librte_eal/common/include/rte_dev.h | 43 ++-----------------------
>  1 file changed, 3 insertions(+), 40 deletions(-)
> 
> diff --git a/lib/librte_eal/common/include/rte_dev.h b/lib/librte_eal/common/include/rte_dev.h
> index a9724dc9181c..e496da440028 100644
> --- a/lib/librte_eal/common/include/rte_dev.h
> +++ b/lib/librte_eal/common/include/rte_dev.h
> @@ -43,54 +43,17 @@ typedef void (*rte_dev_event_cb_fn)(const char *device_name,
>  					enum rte_dev_event_type event,
>  					void *cb_arg);
>  
> -__attribute__((format(printf, 2, 0)))
> -static inline void
> -rte_pmd_debug_trace(const char *func_name, const char *fmt, ...)
> -{
> -	va_list ap;
> -
> -	va_start(ap, fmt);
> -
> -	{
> -		char buffer[vsnprintf(NULL, 0, fmt, ap) + 1];
> -
> -		va_end(ap);
> -
> -		va_start(ap, fmt);
> -		vsnprintf(buffer, sizeof(buffer), fmt, ap);
> -		va_end(ap);
> -
> -		rte_log(RTE_LOG_ERR, RTE_LOGTYPE_PMD, "%s: %s",
> -			func_name, buffer);
> -	}
> -}
> -

Will this break applications that try to use this function? Because it is not
a documented function, is there no guarantee it will be present?

>  /*
>   * Enable RTE_PMD_DEBUG_TRACE() when at least one component relying on the
>   * RTE_*_RET() macros defined below is compiled in debug mode.
>   */
>  #if defined(RTE_LIBRTE_EVENTDEV_DEBUG)
> -#define RTE_PMD_DEBUG_TRACE(...) \
> -	rte_pmd_debug_trace(__func__, __VA_ARGS__)
> +#define RTE_PMD_DEBUG_TRACE(fmt, args...) \
> +	rte_log(RTE_LOG_ERR, RTE_LOGTYPE_PMD, "%s():" fmt, __func__, ## args)

Actually, MSVC does not support named variable arguments either. I think this
will work instead:

  #define RTE_PMD_DEBUG_TRACE(fmt, ...) \
          rte_log(RTE_LOG_ERR, RTE_LOGTYPE_PMD, "%s():" fmt, __func__, __VA_ARGS__)

The previous behavior was "%s: ..." not "%s():". I'm not sure if you meant to
change how the messages are displayed. I don't care either way, but maybe
users of the function would prefer the same format.