Add seed operation for unix RAND method

lib/hcrypto/rand-unix.c

@@ -68,8 +68,33 @@ _hc_unix_device_fd(int flags, const char **fn)
 }
 
 static void
-unix_seed(const void *indata, int size)
+unix_seed(const void *p, int size)
 {
+    const unsigned char *indata = p;
+    ssize_t count;
+    int fd;
+
+    if (size < 0)
+	return;
+    else if (size == 0)
+	return;
+
+    fd = _hc_unix_device_fd(O_RDONLY, NULL);
+    if (fd < 0)
+	return;
+
+    while (size > 0) {
+	count = write(fd, indata, size);
+	if (count < 0 && errno == EINTR)
+	    continue;
+	else if (count <= 0) {
+	    close(fd);
+	    return;
+	}
+	indata += count;
+	size -= count;
+    }
+    close(fd);
 }