[yocto] How can I create a rootfs from packages

[Lorenz B]

Hi,

I compiled an core-image-minimal and put the resulting ipk packages on
a http-server.
I saved the package list, too.

Now I want to rebuild the rootfs image out of those ipk packages.

But if I try with opkg (from the toolchain created with meta-toolchain
recipe) some postinst scripts fail because this scripts wants to write
a file e.g. in /etc which is my real root and not the root directory
(-o option from opkg) for image creation.

I think I have to use pseudo or fakeroot to execute the postinst
scripts but I have no Idea how to intercept the postinst call.

I tried with bitbake, too. But the URL in FEED_URIS are ignored.
Instead the packages are created  (from the sstate-cache) and install
from local feed.

Can anybody help to solve my problem or give me some hints, please?

Thanks,
Lorenz