[yocto] Multiple images/filesystems

[Martin Townsend]

Hi,

I currently have a read only filesystem image. What I would like to do
is have part of the filesystem read/write which is basically a
particular user account, say /home/scratch
To complicate things we have two flash devices,
1) eMMC with ext3 filesystem
2) NAND with ubifs filesystem

So I would have 2 partitions for eMMC one for /home/scratch and the
other for the rest of the rootfs.
For NAND I think I need 2 UBI volumes one contains a UBIFS with
/home/scratch the other with the remaining rootfs.
I think I have to create my own image_type.bbclass file to create the
ubifs and ext3 filesystems but I don't see how I separate out the
/home/scratch from the image's rootfs.  Anyone know what the best way
to do this is.

Many Thanks,
Martin.