[yocto] Can wic split rootfs files across partitions?

[Karl Voelker]

I am trying to build a multi-partition image with wic, with separate
partitions for / and /var. So, the / partition should get all the files
except those under /var, and the /var partition should get the files
under /var.

I thought this was possible because of the suggestion in the docs that
the mntpoint arg of a "part" command could be /usr or /home (see
http://www.yoctoproject.org/docs/2.0/dev-manual/dev-manual.html#command-part-or-partition).

However, after trying a few different things in my wks file, and looking
through a lot of the wic source code, I am starting to wonder if this
kind of thing is not actually supported. If it is supported, is there an
example somewhere? None of the examples in scripts/lib/wic/canned-wks
appear to cover this situation.

Thanks,

Karl Voelker