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

[Wang Nan]

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@xxxxxxxxxxxx>
Signed-off-by: Wang Nan <wangnan0@xxxxxxxxxx>
---
 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;
+
+#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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