add CIRC_SPACE()

diff --git a/sys/dev/pci/drm/include/linux/circ_buf.h b/sys/dev/pci/drm/include/linux/circ_buf.h
index e69de29..4174255 100644 (file)
--- a/sys/dev/pci/drm/include/linux/circ_buf.h
+++ b/sys/dev/pci/drm/include/linux/circ_buf.h
@@ -0,0 +1,8 @@
+/* Public domain. */
+
+#ifndef _LINUX_CIRC_BUF_H
+#define _LINUX_CIRC_BUF_H
+
+#define CIRC_SPACE(h,t,s)      (((t) - ((h)+1)) & ((s)-1))
+
+#endif