tools lib api: Add debug output support

Adding support for warning/info/debug output within libapi code. Adding
following macros:

pr_warning(fmt, ...)
pr_info(fmt, ...)
pr_debug(fmt, ...)

Also adding libapi_set_print function to set above functions. This will
be used in perf to set standard debug handlers for libapi.

Adding 2 header files:
debug.h
- to be used outside libapi, contains
libapi_set_print interface

debug-internal.h
- to be used within libapi, contains
pr_warning/pr_info/pr_debug definitions

Signed-off-by: Jiri Olsa <[e-mail]>
Cc: David Ahern <[e-mail]>
Cc: Namhyung Kim <[e-mail]>
Cc: Peter Zijlstra <[e-mail]>
Link: http://lkml.kernel.org/r/[e-mail]
Signed-off-by: Arnaldo Carvalho de Melo <[e-mail]>

tools/lib/api/Build

···
 libapi-y += fd/
 libapi-y += fs/
 libapi-y += cpu.o
+libapi-y += debug.o

tools/lib/api/Makefile

···
 CFLAGS := $(EXTRA_WARNINGS) $(EXTRA_CFLAGS)
 CFLAGS += -ggdb3 -Wall -Wextra -std=gnu99 -Werror -O6 -U_FORTIFY_SOURCE -D_FORTIFY_SOURCE=2 -fPIC
 CFLAGS += -D_LARGEFILE64_SOURCE -D_FILE_OFFSET_BITS=64
+CFLAGS += -I$(srctree)/tools/lib/api
 
 RM = rm -f
 

tools/lib/api/debug-internal.h

···
+#ifndef __API_DEBUG_INTERNAL_H__
+#define __API_DEBUG_INTERNAL_H__
+
+#include "debug.h"
+
+#define __pr(func, fmt, ...)	\
+do {				\
+	if ((func))		\
+		(func)("libapi: " fmt, ##__VA_ARGS__); \
+} while (0)
+
+extern libapi_print_fn_t __pr_warning;
+extern libapi_print_fn_t __pr_info;
+extern libapi_print_fn_t __pr_debug;
+
+#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__)
+
+#endif /* __API_DEBUG_INTERNAL_H__ */

tools/lib/api/debug.c

···
+#include <stdio.h>
+#include <stdarg.h>
+#include "debug.h"
+#include "debug-internal.h"
+
+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;
+}
+
+libapi_print_fn_t __pr_warning = __base_pr;
+libapi_print_fn_t __pr_info    = __base_pr;
+libapi_print_fn_t __pr_debug;
+
+void libapi_set_print(libapi_print_fn_t warn,
+		      libapi_print_fn_t info,
+		      libapi_print_fn_t debug)
+{
+	__pr_warning = warn;
+	__pr_info    = info;
+	__pr_debug   = debug;
+}

tools/lib/api/debug.h

···
+#ifndef __API_DEBUG_H__
+#define __API_DEBUG_H__
+
+typedef int (*libapi_print_fn_t)(const char *, ...);
+
+void libapi_set_print(libapi_print_fn_t warn,
+		      libapi_print_fn_t info,
+		      libapi_print_fn_t debug);
+
+#endif /* __API_DEBUG_H__ */