libbpf: Add pathname_concat() helper

Move snprintf and len check to common helper pathname_concat() to make the
code simpler.

Signed-off-by: Wang Yufen <wangyufen@huawei.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/1663828124-10437-1-git-send-email-wangyufen@huawei.com

src/libbpf.c

@@ -2097,19 +2097,30 @@ static bool get_map_field_int(const char *map_name, const struct btf *btf,
 	return true;
 }
 
+static int pathname_concat(char *buf, size_t buf_sz, const char *path, const char *name)
+{
+	int len;
+
+	len = snprintf(buf, buf_sz, "%s/%s", path, name);
+	if (len < 0)
+		return -EINVAL;
+	if (len >= buf_sz)
+		return -ENAMETOOLONG;
+
+	return 0;
+}
+
 static int build_map_pin_path(struct bpf_map *map, const char *path)
 {
 	char buf[PATH_MAX];
-	int len;
+	int err;
 
 	if (!path)
 		path = "/sys/fs/bpf";
 
-	len = snprintf(buf, PATH_MAX, "%s/%s", path, bpf_map__name(map));
+	err = pathname_concat(buf, sizeof(buf), path, bpf_map__name(map));
-	if (len < 0)
+	if (err)
-		return -EINVAL;
+		return err;
-	else if (len >= PATH_MAX)
-		return -ENAMETOOLONG;
 
 	return bpf_map__set_pin_path(map, buf);
 }
@@ -7968,17 +7979,9 @@ int bpf_object__pin_maps(struct bpf_object *obj, const char *path)
 			continue;
 
 		if (path) {
-			int len;
+			err = pathname_concat(buf, sizeof(buf), path, bpf_map__name(map));
-
+			if (err)
-			len = snprintf(buf, PATH_MAX, "%s/%s", path,
-				       bpf_map__name(map));
-			if (len < 0) {
-				err = -EINVAL;
 				goto err_unpin_maps;
-			} else if (len >= PATH_MAX) {
-				err = -ENAMETOOLONG;
-				goto err_unpin_maps;
-			}
 			sanitize_pin_path(buf);
 			pin_path = buf;
 		} else if (!map->pin_path) {
@@ -8016,14 +8019,9 @@ int bpf_object__unpin_maps(struct bpf_object *obj, const char *path)
 		char buf[PATH_MAX];
 
 		if (path) {
-			int len;
+			err = pathname_concat(buf, sizeof(buf), path, bpf_map__name(map));
-
+			if (err)
-			len = snprintf(buf, PATH_MAX, "%s/%s", path,
+				return libbpf_err(err);
-				       bpf_map__name(map));
-			if (len < 0)
-				return libbpf_err(-EINVAL);
-			else if (len >= PATH_MAX)
-				return libbpf_err(-ENAMETOOLONG);
 			sanitize_pin_path(buf);
 			pin_path = buf;
 		} else if (!map->pin_path) {
@@ -8041,6 +8039,7 @@ int bpf_object__unpin_maps(struct bpf_object *obj, const char *path)
 int bpf_object__pin_programs(struct bpf_object *obj, const char *path)
 {
 	struct bpf_program *prog;
+	char buf[PATH_MAX];
 	int err;
 
 	if (!obj)
@@ -8052,17 +8051,9 @@ int bpf_object__pin_programs(struct bpf_object *obj, const char *path)
 	}
 
 	bpf_object__for_each_program(prog, obj) {
-		char buf[PATH_MAX];
+		err = pathname_concat(buf, sizeof(buf), path, prog->name);
-		int len;
+		if (err)
-
-		len = snprintf(buf, PATH_MAX, "%s/%s", path, prog->name);
-		if (len < 0) {
-			err = -EINVAL;
 			goto err_unpin_programs;
-		} else if (len >= PATH_MAX) {
-			err = -ENAMETOOLONG;
-			goto err_unpin_programs;
-		}
 
 		err = bpf_program__pin(prog, buf);
 		if (err)
@@ -8073,13 +8064,7 @@ int bpf_object__pin_programs(struct bpf_object *obj, const char *path)
 
 err_unpin_programs:
 	while ((prog = bpf_object__prev_program(obj, prog))) {
-		char buf[PATH_MAX];
+		if (pathname_concat(buf, sizeof(buf), path, prog->name))
-		int len;
-
-		len = snprintf(buf, PATH_MAX, "%s/%s", path, prog->name);
-		if (len < 0)
-			continue;
-		else if (len >= PATH_MAX)
 			continue;
 
 		bpf_program__unpin(prog, buf);
@@ -8098,13 +8083,10 @@ int bpf_object__unpin_programs(struct bpf_object *obj, const char *path)
 
 	bpf_object__for_each_program(prog, obj) {
 		char buf[PATH_MAX];
-		int len;
 
-		len = snprintf(buf, PATH_MAX, "%s/%s", path, prog->name);
+		err = pathname_concat(buf, sizeof(buf), path, prog->name);
-		if (len < 0)
+		if (err)
-			return libbpf_err(-EINVAL);
+			return libbpf_err(err);
-		else if (len >= PATH_MAX)
-			return libbpf_err(-ENAMETOOLONG);
 
 		err = bpf_program__unpin(prog, buf);
 		if (err)