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

[Stephen Hemminger <stephen@networkplumber.org>]

On Fri, 12 Oct 2018 14:43:57 +0200
Adrien Mazarguil <adrien.mazarguil@6wind.com> wrote:

> 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.
> > >   
> >   
> 

Since zero varadic macros is a GNU extension, maybe just adding GNU source?