i considered submitting this patch anonomously since it's so ugly.

the problem is that the kfs file structure depends on the architecture,
because the Dentry structure has an embedded structure at a 2 byte
boundary.  this means that 32-bit machines will pad it out with 2
extra bytes, and 64-bit machiens will pad it with 6 extra bytes.

to preserve the on-disk layout, the c structure was #pragma packed
and explicit padding was added as necessary.

adding proper marshalling code looked to be a bit daunting, but
that seems like a better long-term solution.

Reference: /n/atom/patch/applied2013/kfs64bitclean
Date: Mon Oct 14 23:34:42 CES 2013
Signed-off-by: quanstro@quanstro.net

--- /sys/src/cmd/disk/kfs/portdat.h	Mon Oct 14 23:31:28 2013
+++ /sys/src/cmd/disk/kfs/portdat.h	Mon Oct 14 23:31:28 2013
@@ -39,7 +39,16 @@
 	long	version;
 };
 
+/*
+ * oh rats!  this structure deeply assumes a 32-bit machine.
+ * to make this work for 64-bit, without breaking old kfs
+ * images, some dirty tricks are necessary.  first we have to
+ * pack the structure, but that packs too well,  the short
+ * "badplanning" fills in the traditional hole.
+ */
+
 /* DONT TOUCH, this is the disk structure */
+#pragma pack on
 struct	Dentry
 {
 	char	name[NAMELEN];
@@ -53,6 +62,7 @@
 		#define	DREAD	0x4
 		#define	DWRITE	0x2
 		#define	DEXEC	0x1
+	short	badplanning;
 	Qid9p1	qid;
 	long	size;
 	long	dblock[NDBLOCK];
@@ -61,6 +71,7 @@
 	long	atime;
 	long	mtime;
 };
+#pragma pack off
 
 /* DONT TOUCH, this is the disk structure */
 struct	Tag