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

[Declan Doherty <declan.doherty@intel.com>]

On 09/11/15 14:02, Richardson, Bruce wrote:
>
>
>> -----Original Message-----
>> From: Adrien Mazarguil [mailto:adrien.mazarguil@6wind.com]
>> Sent: Monday, November 9, 2015 1:39 PM
>> To: Richardson, Bruce <bruce.richardson@intel.com>
>> Cc: Stephen Hemminger <stephen@networkplumber.org>; Thomas Monjalon
>> <thomas.monjalon@6wind.com>; dev@dpdk.org
>> Subject: Re: [dpdk-dev] [PATCH v3 2/4] ethdev: move error checking macros
>> to header
>>
>> On Fri, Nov 06, 2015 at 05:22:27PM +0000, Bruce Richardson wrote:
>>> 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?
>>
>> Such a function shouldn't malloc() anything. The entire line should fit on
>> the stack (crashing is fine if it does not, then it's probably a bug). We
>> did something in two passes along these lines in mlx5_defs.h (not pretty
>> but
>> quite useful):
>>
>>   /* Allocate a buffer on the stack and fill it with a printf format
>> string. */
>>   #define MKSTR(name, ...) \
>>           char name[snprintf(NULL, 0, __VA_ARGS__) + 1]; \
>>           \
>>           snprintf(name, sizeof(name), __VA_ARGS__)
>>
>> Untested but I guess modifying that function accordingly would look like:
>>
>>   static inline void
>>   rte_pmd_debug_trace(const char *func_name, const char *fmt, ...)
>>   {
>>           va_list ap;
>>           va_start(ap, fmt);
>>
>>           static __thread char buffer[vsnprintf(NULL, 0, fmt, ap)];
>>
>>           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);
>>   }
>>
>
> Looks a much better option.
>
>  From this, though, I assume then that we are only looking to support the -pedantic flag in conjuction with c99 mode or above. Supporting -pedantic with the pre-gcc-5 versions won't allow that to work though, as variably sized arrays only came in with c99, and were gnu extensions before that.
>
> Regards,
> /Bruce
>

I had made some similar changes in the cryptodev patch set to allow 
these macros to be shared between the ethdev and cryptodev, but I wasn't 
aware of the -pedantic build issues. I've incorporate the changes from 
patch 1 & 2 discussed here into the cryptodev patch set. See patch 2/10 
(http://dpdk.org/ml/archives/dev/2015-November/027888.html) for the 
implementation of the rte_pmf_debug_trace function. Any comments or 
ack's are welcome :)

Declan