[RFC PATCH v3 07/37] bpf tools: Allow caller to set printing function

[Wang Nan <wangnan0@huawei.com>]

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.

Signed-off-by: Wang Nan <wangnan0@huawei.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 bebe99a..d7a7869 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -8,8 +8,51 @@
  */
 
 #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 10845a0..eb306c0 100644
--- a/tools/lib/bpf/libbpf.h
+++ b/tools/lib/bpf/libbpf.h
@@ -9,4 +9,8 @@
 #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