move iterate_on_dir() from e2fsprogs to libbb

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

libbb/iterate_on_dir.c

@@ -0,0 +1,28 @@
+/* vi: set sw=4 ts=4: */
+/*
+ * See README for additional information
+ *
+ * Licensed under GPLv2, see file LICENSE in this source tree.
+ */
+//kbuild:lib-y += iterate_on_dir.o
+
+#include "libbb.h"
+
+/* Iterate a function on each entry of a directory */
+int FAST_FUNC iterate_on_dir(const char *dir_name,
+		int FAST_FUNC (*func)(const char *, struct dirent *, void *),
+		void *private)
+{
+	DIR *dir;
+	struct dirent *de;
+
+	dir = opendir(dir_name);
+	if (dir == NULL) {
+		return -1;
+	}
+	while ((de = readdir(dir)) != NULL) {
+		func(dir_name, de, private);
+	}
+	closedir(dir);
+	return 0;
+}