diff --git a/src/libbio/bbuffered.c b/src/libbio/bbuffered.c
new file mode 100644
index 0000000..dfc0cf5
--- /dev/null
+++ b/src/libbio/bbuffered.c
@@ -0,0 +1,20 @@
+#include	"lib9.h"
+#include	<bio.h>
+
+int
+Bbuffered(Biobuf *bp)
+{
+	switch(bp->state) {
+	case Bracteof:
+	case Bractive:
+		return -bp->icount;
+
+	case Bwactive:
+		return bp->bsize + bp->ocount;
+
+	case Binactive:
+		return 0;
+	}
+	fprint(2, "Bbuffered: unknown state %d\n", bp->state);
+	return 0;
+}