linux-kernel - Re: [RFC PATCH v4 05/29] bpf tools: Allow caller to set printing function

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Date:	Fri, 29 May 2015 22:35:47 +0900
From:	Namhyung Kim <namhyung@...nel.org>
To:	Wang Nan <wangnan0@...wei.com>
Cc:	paulus@...ba.org, a.p.zijlstra@...llo.nl, mingo@...hat.com,
	acme@...nel.org, jolsa@...nel.org, dsahern@...il.com,
	daniel@...earbox.net, brendan.d.gregg@...il.com,
	masami.hiramatsu.pt@...achi.com, lizefan@...wei.com,
	linux-kernel@...r.kernel.org, pi3orama@....com
Subject: Re: [RFC PATCH v4 05/29] bpf tools: Allow caller to set printing
 function

Hi Wang,

On Wed, May 27, 2015 at 05:19:40AM +0000, Wang Nan wrote:
> By libbpf_set_print(), users of libbpf are allowed to register he/she
> own debug, info and warning printing functions. Libbpf will use those
> functions to print messages. If not provided, default info and warning
> printing functions are fprintf(stderr, ...); defailt debug printing
> is NULL.
> 
> This API is designed to be used by perf, enables it to register its own
> logging functions to make all logs uniform, instead of separated
> logging level control.
> 
> Acked-by: Alexei Starovoitov <ast@...mgrid.com>
> Signed-off-by: Wang Nan <wangnan0@...wei.com>
> ---
>  tools/lib/bpf/libbpf.c | 43 +++++++++++++++++++++++++++++++++++++++++++
>  tools/lib/bpf/libbpf.h |  4 ++++
>  2 files changed, 47 insertions(+)
> 
> diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
> index c08d6bc..49091c3 100644
> --- a/tools/lib/bpf/libbpf.c
> +++ b/tools/lib/bpf/libbpf.c
> @@ -7,8 +7,51 @@
>   */
>  
>  #include <stdlib.h>
> +#include <stdio.h>
> +#include <stdarg.h>
> +#include <string.h>
>  #include <unistd.h>
>  #include <asm/unistd.h>
>  #include <linux/bpf.h>
>  
>  #include "libbpf.h"
> +
> +#define __printf(a, b)	__attribute__((format(printf, a, b)))
> +
> +__printf(1, 2)
> +static int __base_pr(const char *format, ...)
> +{
> +	va_list args;
> +	int err;
> +
> +	va_start(args, format);
> +	err = vfprintf(stderr, format, args);
> +	va_end(args);
> +	return err;
> +}
> +
> +static __printf(1, 2) int (*__pr_warning)(const char *format, ...) =
> +	__base_pr;
> +static __printf(1, 2) int (*__pr_info)(const char *format, ...) =
> +	__base_pr;
> +static __printf(1, 2) int (*__pr_debug)(const char *format, ...) =
> +	NULL;

What about using typedef for this.. like print_fn_t ?

Thanks,
Namhyung


> +
> +#define __pr(func, fmt, ...)	\
> +do { 				\
> +	if ((func))	\
> +		(func)("libbpf: " fmt, ##__VA_ARGS__); \
> +} while(0)
> +
> +#define pr_warning(fmt, ...)	__pr(__pr_warning, fmt, ##__VA_ARGS__)
> +#define pr_info(fmt, ...)	__pr(__pr_info, fmt, ##__VA_ARGS__)
> +#define pr_debug(fmt, ...)	__pr(__pr_debug, fmt, ##__VA_ARGS__)
> +
> +void libbpf_set_print(int (*warn)(const char *format, ...),
> +		      int (*info)(const char *format, ...),
> +		      int (*debug)(const char *format, ...))
> +{
> +	__pr_warning = warn;
> +	__pr_info = info;
> +	__pr_debug = debug;
> +}
> diff --git a/tools/lib/bpf/libbpf.h b/tools/lib/bpf/libbpf.h
> index a6f46d9..430b122 100644
> --- a/tools/lib/bpf/libbpf.h
> +++ b/tools/lib/bpf/libbpf.h
> @@ -8,4 +8,8 @@
>  #ifndef __BPF_LIBBPF_H
>  #define __BPF_LIBBPF_H
>  
> +void libbpf_set_print(int (*warn)(const char *format, ...),
> +		      int (*info)(const char *format, ...),
> +		      int (*debug)(const char *format, ...));
> +
>  #endif
> -- 
> 1.8.3.4
> 
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