Re: [dpdk-dev] [PATCH] ethdev: add function name to log message

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

On Fri, Oct 12, 2018 at 11:45:01AM +0100, Ferruh Yigit wrote:
> On 10/12/2018 11:42 AM, Ferruh Yigit wrote:
> > On 10/11/2018 6:59 PM, Stephen Hemminger wrote:
> >> @@ -161,8 +161,9 @@ extern "C" {
> >>  
> >>  extern int rte_eth_dev_logtype;
> >>  
> >> -#define RTE_ETHDEV_LOG(level, ...) \
> >> -	rte_log(RTE_LOG_ ## level, rte_eth_dev_logtype, "" __VA_ARGS__)
> >> +#define RTE_ETHDEV_LOG(level, fmt, ...)		\
> >> +	rte_log(RTE_LOG_ ## level, rte_eth_dev_logtype, \
> >> +		"%s():" fmt, __func__, ## __VA_ARGS__)
> > 
> > +1 to adding function name, but
> > 
> > failsafe is giving build error [1] with clang because of ## usage [2], that is
> > why I add this as ` "" __VA_ARGS__` at first place but you can't do this trick
> > if __VA_ARGS__ used after fmt.
> > 
> > I am not aware of a solution for this, __VA_OPT__(,) also didn't worked with clang.
> 
> +cc Adrien & Gaetan,
> 
> I saw Adrien put some "workaround" to this for mlx5

Yes, through RTE_FMT() (rte_common.h). Something like this:

 #define RTE_ETHDEV_LOG(level, fmt, ...) \
     rte_log(RTE_LOG_ ## level, \
             rte_eth_dev_logtype, \
             "%s():" fmt, \
             __func__, \
             ## __VA_ARGS__)

Can be rewritten like that:

 #define RTE_ETHDEV_LOG(level, ...) \
     rte_log(RTE_LOG_ ## level, \
             rte_eth_dev_logtype, \
             RTE_FMT("%s():" RTE_FMT_HEAD(__VA_ARGS__,), \
                     __func__, \
                     RTE_FMT_TAIL(__VA_ARGS__,)))

Although not too pretty and convenient, it does the job. In short:

- Remove "fmt" argument from prototype.
- Enclose format string and its arguments in RTE_FMT().
- Replace "fmt" with RTE_FMT_HEAD(__VA_ARGS__,).
- Replace "## __VA_ARGS__" with RTE_FMT_TAIL(__VA_ARGS__,).
- Yes, trailing commas are mandatory in RTE_FMT_(HEAD|TAIL)().
- Note it quietly appends a dummy "%.0s" argument to the format string.

> > [1]
> > .../build/include/rte_ethdev.h:166:26: error: token pasting of ',' and
> > __VA_ARGS__ is a GNU extension [-Werror,-Wgnu-zero-variadic-macro-arguments]
> >                 "%s():" fmt, __func__, ## __VA_ARGS__)
> >                                        ^
> > 
> > [2]
> > This seems because of "-pedantic" argument driver uses, and other PMDs using
> > "-pedantic", like mlx,  will have same error although they are disable by
> > default and error not observed in default build.
> > 
> 

-- 
Adrien Mazarguil
6WIND