diff --git a/tools/perf/util/util.c b/tools/perf/util/util.c
index 6ea0b4a..b1d5376 100644
--- a/tools/perf/util/util.c
+++ b/tools/perf/util/util.c
@@ -152,16 +152,14 @@
 	return value;
 }
 
-/*
- * Read exactly 'n' bytes or return an error.
- */
-ssize_t readn(int fd, void *buf, size_t n)
+static ssize_t ion(bool is_read, int fd, void *buf, size_t n)
 {
 	void *buf_start = buf;
 	size_t left = n;
 
 	while (left) {
-		ssize_t ret = read(fd, buf, left);
+		ssize_t ret = is_read ? read(fd, buf, left) :
+					write(fd, buf, left);
 
 		if (ret <= 0)
 			return ret;
@@ -174,6 +172,22 @@
 	return n;
 }
 
+/*
+ * Read exactly 'n' bytes or return an error.
+ */
+ssize_t readn(int fd, void *buf, size_t n)
+{
+	return ion(true, fd, buf, n);
+}
+
+/*
+ * Write exactly 'n' bytes or return an error.
+ */
+ssize_t writen(int fd, void *buf, size_t n)
+{
+	return ion(false, fd, buf, n);
+}
+
 size_t hex_width(u64 v)
 {
 	size_t n = 1;