To build YAFFS in the Linux kernel tree you need to run the patch-ker.sh
script from the yaffs source directory, giving your choice as to whether
you wish to copy (c) or link (l) the code and the path to your kernel
sources, e.g:

./patch-ker.sh c /usr/src/linux

This will copy the yaffs files into fs/yaffs2 and modify the Kconfig
and Makefiles in the fs directory.

./patch-ker.sh l /usr/src/linux

This does the same as the above but makes symbolic links instead.

After you've run the script, go back to your normal kernel making procedure
and configure the yaffs settings you want.

Prolems? Contact the yaffs mailing list:

http://www.aleph1.co.uk/mailman/listinfo/yaffs