[PATCH bpf-next 4/9] libbpf: add libbpf_swap_print to get previous print func

[Andrii Nakryiko <andriin@fb.com>]

libbpf_swap_print allows to restore previously set print function.
This is useful when running many independent test with one default print
function, but overriding log verbosity for particular subset of tests.

Signed-off-by: Andrii Nakryiko <andriin@fb.com>
---
 tools/lib/bpf/libbpf.c   | 8 ++++++++
 tools/lib/bpf/libbpf.h   | 1 +
 tools/lib/bpf/libbpf.map | 5 +++++
 3 files changed, 14 insertions(+)

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index 8741c39adb1c..0c254b6c9685 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -79,6 +79,14 @@ void libbpf_set_print(libbpf_print_fn_t fn)
 	__libbpf_pr = fn;
 }
 
+libbpf_print_fn_t libbpf_swap_print(libbpf_print_fn_t fn)
+{
+	libbpf_print_fn_t old_print_fn = __libbpf_pr;
+
+	__libbpf_pr = fn;
+	return old_print_fn;
+}
+
 __printf(2, 3)
 void libbpf_print(enum libbpf_print_level level, const char *format, ...)
 {
diff --git a/tools/lib/bpf/libbpf.h b/tools/lib/bpf/libbpf.h
index 5cbf459ece0b..4e0aa893571f 100644
--- a/tools/lib/bpf/libbpf.h
+++ b/tools/lib/bpf/libbpf.h
@@ -58,6 +58,7 @@ typedef int (*libbpf_print_fn_t)(enum libbpf_print_level level,
 				 const char *, va_list ap);
 
 LIBBPF_API void libbpf_set_print(libbpf_print_fn_t fn);
+LIBBPF_API libbpf_print_fn_t libbpf_swap_print(libbpf_print_fn_t fn);
 
 /* Hide internal to user */
 struct bpf_object;
diff --git a/tools/lib/bpf/libbpf.map b/tools/lib/bpf/libbpf.map
index f9d316e873d8..e211c38ddc43 100644
--- a/tools/lib/bpf/libbpf.map
+++ b/tools/lib/bpf/libbpf.map
@@ -184,3 +184,8 @@ LIBBPF_0.0.4 {
 		perf_buffer__new_raw;
 		perf_buffer__poll;
 } LIBBPF_0.0.3;
+
+LIBBPF_0.0.5 {
+	global:
+		libbpf_swap_print;
+} LIBBPF_0.0.4;
-- 
2.17.1