[PATCH bpf-next] selftests/bpf: cgroup_helpers.c: Fix strncpy() fortify warning

[Rong Tao <rtoax@foxmail.com>]

From: Rong Tao <rongtao@cestc.cn>

Move libbpf_strlcpy() to libbpf_common.h, and replace strncpy() with
libbpf_strlcpy(), fix compile warning.

We can't use libbpf_internal.h directly, because it introduces a lot of
header dependency issues. So move libbpf_strlcpy() into libbpf_common.h,
and if you need to use the libbpf_strlcpy() function, you need to include
the header file libbpf.h

How to reproduce this compilation warning:

$ make -C samples/bpf
cgroup_helpers.c: In function ‘__enable_controllers’:
cgroup_helpers.c:80:17: warning: ‘strncpy’ specified bound 4097 equals destination size [-Wstringop-truncation]
   80 |                 strncpy(enable, controllers, sizeof(enable));
      |                 ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Signed-off-by: Rong Tao <rongtao@cestc.cn>
---
 tools/lib/bpf/libbpf_common.h                | 19 +++++++++++++++++++
 tools/lib/bpf/libbpf_internal.h              | 19 -------------------
 tools/testing/selftests/bpf/cgroup_helpers.c |  3 ++-
 tools/testing/selftests/bpf/xsk.c            | 19 -------------------
 4 files changed, 21 insertions(+), 39 deletions(-)

diff --git a/tools/lib/bpf/libbpf_common.h b/tools/lib/bpf/libbpf_common.h
index 9a7937f339df..9d5132e0bec9 100644
--- a/tools/lib/bpf/libbpf_common.h
+++ b/tools/lib/bpf/libbpf_common.h
@@ -70,4 +70,23 @@
 		};							    \
 	})
 
+/* Copy up to sz - 1 bytes from zero-terminated src string and ensure that dst
+ * is zero-terminated string no matter what (unless sz == 0, in which case
+ * it's a no-op). It's conceptually close to FreeBSD's strlcpy(), but differs
+ * in what is returned. Given this is internal helper, it's trivial to extend
+ * this, when necessary. Use this instead of strncpy inside libbpf source code.
+ */
+static inline void libbpf_strlcpy(char *dst, const char *src, size_t sz)
+{
+	size_t i;
+
+	if (sz == 0)
+		return;
+
+	sz--;
+	for (i = 0; i < sz && src[i]; i++)
+		dst[i] = src[i];
+	dst[i] = '\0';
+}
+
 #endif /* __LIBBPF_LIBBPF_COMMON_H */
diff --git a/tools/lib/bpf/libbpf_internal.h b/tools/lib/bpf/libbpf_internal.h
index 377642ff51fc..902110ffb7a6 100644
--- a/tools/lib/bpf/libbpf_internal.h
+++ b/tools/lib/bpf/libbpf_internal.h
@@ -191,25 +191,6 @@ static inline void *libbpf_reallocarray(void *ptr, size_t nmemb, size_t size)
 	return realloc(ptr, total);
 }
 
-/* Copy up to sz - 1 bytes from zero-terminated src string and ensure that dst
- * is zero-terminated string no matter what (unless sz == 0, in which case
- * it's a no-op). It's conceptually close to FreeBSD's strlcpy(), but differs
- * in what is returned. Given this is internal helper, it's trivial to extend
- * this, when necessary. Use this instead of strncpy inside libbpf source code.
- */
-static inline void libbpf_strlcpy(char *dst, const char *src, size_t sz)
-{
-	size_t i;
-
-	if (sz == 0)
-		return;
-
-	sz--;
-	for (i = 0; i < sz && src[i]; i++)
-		dst[i] = src[i];
-	dst[i] = '\0';
-}
-
 __u32 get_kernel_version(void);
 
 struct btf;
diff --git a/tools/testing/selftests/bpf/cgroup_helpers.c b/tools/testing/selftests/bpf/cgroup_helpers.c
index e914cc45b766..e3bfe2b13018 100644
--- a/tools/testing/selftests/bpf/cgroup_helpers.c
+++ b/tools/testing/selftests/bpf/cgroup_helpers.c
@@ -11,6 +11,7 @@
 #include <fcntl.h>
 #include <unistd.h>
 #include <ftw.h>
+#include <bpf/libbpf.h>
 
 #include "cgroup_helpers.h"
 
@@ -77,7 +78,7 @@ static int __enable_controllers(const char *cgroup_path, const char *controllers
 		enable[len] = 0;
 		close(fd);
 	} else {
-		strncpy(enable, controllers, sizeof(enable));
+		libbpf_strlcpy(enable, controllers, sizeof(enable));
 	}
 
 	snprintf(path, sizeof(path), "%s/cgroup.subtree_control", cgroup_path);
diff --git a/tools/testing/selftests/bpf/xsk.c b/tools/testing/selftests/bpf/xsk.c
index 0b3ff49c740d..4b6890e2a0a9 100644
--- a/tools/testing/selftests/bpf/xsk.c
+++ b/tools/testing/selftests/bpf/xsk.c
@@ -521,25 +521,6 @@ static int xsk_create_bpf_link(struct xsk_socket *xsk)
 	return 0;
 }
 
-/* Copy up to sz - 1 bytes from zero-terminated src string and ensure that dst
- * is zero-terminated string no matter what (unless sz == 0, in which case
- * it's a no-op). It's conceptually close to FreeBSD's strlcpy(), but differs
- * in what is returned. Given this is internal helper, it's trivial to extend
- * this, when necessary. Use this instead of strncpy inside libbpf source code.
- */
-static inline void libbpf_strlcpy(char *dst, const char *src, size_t sz)
-{
-        size_t i;
-
-        if (sz == 0)
-                return;
-
-        sz--;
-        for (i = 0; i < sz && src[i]; i++)
-                dst[i] = src[i];
-        dst[i] = '\0';
-}
-
 static int xsk_get_max_queues(struct xsk_socket *xsk)
 {
 	struct ethtool_channels channels = { .cmd = ETHTOOL_GCHANNELS };
-- 
2.31.1