netdev - [PATCH v3 bpf-next 4/9] libbpf: return previous print callback from libbpf_set

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Date:   Sat, 27 Jul 2019 20:25:26 -0700
From:   Andrii Nakryiko <andriin@...com>
To:     <bpf@...r.kernel.org>, <netdev@...r.kernel.org>, <ast@...com>,
        <daniel@...earbox.net>, <sdf@...ichev.me>
CC:     <andrii.nakryiko@...il.com>, <kernel-team@...com>,
        Andrii Nakryiko <andriin@...com>
Subject: [PATCH v3 bpf-next 4/9] libbpf: return previous print callback from libbpf_set_print

By returning previously set print callback from libbpf_set_print, it's
possible to restore it, eventually. 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@...com>
---
 tools/lib/bpf/libbpf.c | 5 ++++-
 tools/lib/bpf/libbpf.h | 2 +-
 2 files changed, 5 insertions(+), 2 deletions(-)

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index 8741c39adb1c..ead915aec349 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -74,9 +74,12 @@ static int __base_pr(enum libbpf_print_level level, const char *format,
 
 static libbpf_print_fn_t __libbpf_pr = __base_pr;
 
-void libbpf_set_print(libbpf_print_fn_t fn)
+libbpf_print_fn_t libbpf_set_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)
diff --git a/tools/lib/bpf/libbpf.h b/tools/lib/bpf/libbpf.h
index 5cbf459ece0b..8a9d462a6f6d 100644
--- a/tools/lib/bpf/libbpf.h
+++ b/tools/lib/bpf/libbpf.h
@@ -57,7 +57,7 @@ enum libbpf_print_level {
 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_set_print(libbpf_print_fn_t fn);
 
 /* Hide internal to user */
 struct bpf_object;
-- 
2.17.1