YAFFS1 codebase provides a sendfile method while YAFFS2 does not.  Any
reason not to?  Without it, loopback mounts of files in yaffs fails.
Suggested patch below has been minimally sanity tested with a loopback
mount of a VFAT filesystem contained in a YAFFS file (which hints as to
why folks want to do this -- bad block aware FAT).

Thanks -- Todd

Index: yaffs_fs.c
===================================================================
RCS file: /home/aleph1/cvs/yaffs2/yaffs_fs.c,v
retrieving revision 1.38
diff -u -r1.38 yaffs_fs.c
--- yaffs_fs.c	15 Dec 2005 20:27:56 -0000	1.38
+++ yaffs_fs.c	5 Jan 2006 21:16:12 -0000
@@ -171,6 +171,10 @@
 	.mmap = generic_file_mmap,
 	.flush = yaffs_file_flush,
 	.fsync = yaffs_sync_object,
+#if (LINUX_VERSION_CODE > KERNEL_VERSION(2,5,0))
+	.sendfile = generic_file_sendfile,
+#endif
+
 };
 
 static struct inode_operations yaffs_file_inode_operations = {