oops.  i read the last diff backwards, and my conclusion was wrong.

Reference: /n/atom/patch/applied/fixarenas
Date: Thu Mar 20 15:47:12 CET 2014
Signed-off-by: quanstro@quanstro.net

--- /sys/src/cmd/venti/srv/fixarenas.c	Thu Mar 20 15:46:54 2014
+++ /sys/src/cmd/venti/srv/fixarenas.c	Thu Mar 20 15:46:54 2014
@@ -130,12 +130,12 @@
 	int i, j, k, n;
 
 	if(offset >= partend){
-		memset(buf, 0xFB, sizeof buf);
+		memset(buf, 0xFB, len);
 		return buf;
 	}
 	
 	if(offset+len > partend){
-		memset(buf, 0xFB, sizeof buf);
+		memset(buf, 0xFB, len);
 		len = partend - offset;
 	}