lib: c: io: implement standard FILE and DIR interfaces

lib/libc/io/stdio/readdir.c

@@ -0,0 +1,35 @@
+#include "dir.h"
+
+#include <dirent.h>
+#include <errno.h>
+#include <fcntl.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+
+struct dirent *readdir(struct __opaque_dir *dirp)
+{
+	int result = __libc_dir_move_next(dirp);
+	if (result < 0) {
+		dirp->d_flags |= DIR_ERR;
+		__set_errno(-result);
+		return NULL;
+	}
+
+	if (result > 0) {
+		return &dirp->d_current;
+	}
+
+	result = __libc_dir_refill(dirp);
+	if (result < 0) {
+		dirp->d_flags |= DIR_ERR;
+		__set_errno(-result);
+		return NULL;
+	}
+
+	if (!dirp->d_buf_datalen) {
+		return NULL;
+	}
+
+	return &dirp->d_current;
+}