Re: [PATCH bpf-next v1 09/11] libbpf: Add bpf_stream_printk() macro

[Eduard Zingerman <eddyz87@gmail.com>]

On Wed, 2025-05-07 at 10:17 -0700, Kumar Kartikeya Dwivedi wrote:

[...]

> diff --git a/tools/lib/bpf/bpf_helpers.h b/tools/lib/bpf/bpf_helpers.h
> index a50773d4616e..1a748c21e358 100644
> --- a/tools/lib/bpf/bpf_helpers.h
> +++ b/tools/lib/bpf/bpf_helpers.h

[...]

>  /* Use __bpf_printk when bpf_printk call has 3 or fewer fmt args
> - * Otherwise use __bpf_vprintk
> + * Otherwise use __bpf_vprintk. Virtualize choices so stream printk
> + * can override it to bpf_stream_vprintk.
>   */
> -#define ___bpf_pick_printk(...) \
> -	___bpf_nth(_, ##__VA_ARGS__, __bpf_vprintk, __bpf_vprintk, __bpf_vprintk,	\
> -		   __bpf_vprintk, __bpf_vprintk, __bpf_vprintk, __bpf_vprintk,		\
> -		   __bpf_vprintk, __bpf_vprintk, __bpf_printk /*3*/, __bpf_printk /*2*/,\
> -		   __bpf_printk /*1*/, __bpf_printk /*0*/)
> +#define ___bpf_pick_printk(choice, choice_3, ...)			\
> +	___bpf_nth(_, ##__VA_ARGS__, choice, choice, choice,		\
> +		   choice, choice, choice, choice,			\
> +		   choice, choice, choice_3 /*3*/, choice_3 /*2*/,	\
> +		   choice_3 /*1*/, choice_3 /*0*/)
>  
>  /* Helper macro to print out debug messages */
> -#define bpf_printk(fmt, args...) ___bpf_pick_printk(args)(fmt, ##args)
> +#define __bpf_trace_printk(fmt, args...) \
> +	___bpf_pick_printk(__bpf_vprintk, __bpf_printk, args)(fmt, ##args)
> +#define __bpf_stream_printk(stream, fmt, args...) \
> +	___bpf_pick_printk(__bpf_stream_vprintk, __bpf_stream_vprintk, args)(stream, fmt, ##args)
                           ^^^^^^^^^^^^^^^^^^^^  ^^^^^^^^^^^^^^^^^^^^
                           These two parameters are identical,
                           why is ___bpf_pick_printk is necessary in such case?
> +
> +#define bpf_stream_printk(stream, fmt, args...) __bpf_stream_printk(stream, fmt, ##args)
> +
> +#define bpf_printk(arg, args...) __bpf_trace_printk(arg, ##args)
>  
>  struct bpf_iter_num;
>