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

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

On Fri, Nov 06, 2015 at 05:10:07PM +0000, Bruce Richardson wrote:
> On Thu, Nov 05, 2015 at 04:09:18PM +0100, Adrien Mazarguil wrote:
> > 
> > I won't argue against this as it's obviously more complex than the original
> > method, however note that users of the RTE_PMD_DEBUG_TRACE() macro do not
> > have to modify their code. They shouldn't care about the implementation.
> > 
> > Also note that we can do much cleaner code if we drop the all macros
> > implementation using a (much easier to debug) static inline function,
> > only perhaps with a wrapper macro that provides __LINE__, __func__ and
> > __FILE__ as arguments. Nontrival code shouldn't be done in macros anyway.
> > 
> Getting something working with __FILE__ and probably __LINE__ would be easy enough
> with a helper macro, but __func__ is not so easy as it's not a preprocessor symbol
> [since the pre-processor has no idea what function you are in].
> 
> However, using func, here is the best I've come up with so far. It's not that
> pretty, but it's probably easier to work with than the macro version.
> 
>  #ifdef RTE_LIBRTE_ETHDEV_DEBUG
>  -#define RTE_PMD_DEBUG_TRACE(fmt, args...) \
>  -               RTE_LOG(ERR, PMD, "%s: " fmt, __func__, ## args)
>  +#define RTE_PMD_DEBUG_TRACE(...) \
>  +               rte_pmd_debug_trace(__func__, __VA_ARGS__)
>  +
>  +static inline void
>  +rte_pmd_debug_trace(const char *func_name, const char *fmt, ...)
>  +{
>  +       static __thread char buffer[128];
>  +       char *out_buf = buffer;
>  +       unsigned count;
>  +       va_list ap;
>  +
>  +       count = snprintf(buffer, sizeof(buffer), "%s: %s", func_name, fmt);
>  +       if (count >= sizeof(buffer)) { // truncated output
>  +               char *new_buf = malloc(count + 1);
>  +               if (new_buf == NULL) // no memory, just print 128 chars
>  +                       goto print_buffer;
>  +               snprintf(new_buf, count + 1, "%s: %s", func_name, fmt);
>  +               va_start(ap, fmt);
>  +               rte_vlog(RTE_LOG_ERR, RTE_LOGTYPE_PMD, buffer, ap);
>  +               va_end(ap);
>  +               free(new_buf);
>  +               return;
>  +       }
>  +
>  +print_buffer:
>  +       va_start(ap, fmt);
>  +       rte_vlog(RTE_LOG_ERR, RTE_LOGTYPE_PMD, out_buf, ap);
>  +       va_end(ap);
>  +}
>   #else
>   #define RTE_PMD_DEBUG_TRACE(fmt, args...)
>   #endif
> 
> Comments or improvements?
> 
> /Bruce

And here's the version if we are happy to have file and line number instead of
function name. I think this might be the best option.

/Bruce

 #ifdef RTE_LIBRTE_ETHDEV_DEBUG
 -#define RTE_PMD_DEBUG_TRACE(fmt, args...) \
 -               RTE_LOG(ERR, PMD, "%s: " fmt, __func__, ## args)
 +#define RTE_PMD_DEBUG_TRACE(...) \
 +       RTE_LOG(ERR, PMD, __FILE__", " RTE_STR(__LINE__) ": " __VA_ARGS__)
  #else
 -#define RTE_PMD_DEBUG_TRACE(fmt, args...)
 +#define RTE_PMD_DEBUG_TRACE(...)
  #endif