> -----Original Message----- > From: Adrien Mazarguil [mailto:adrien.mazarguil at 6wind.com] > Sent: Monday, November 9, 2015 1:39 PM > To: Richardson, Bruce <bruce.richardson at intel.com> > Cc: Stephen Hemminger <stephen at networkplumber.org>; Thomas Monjalon > <thomas.monjalon at 6wind.com>; dev at 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