[yocto] Question about wic partition creation

[Nicolas Bigaouette]

We are using Yocto (jethro and krogoth) to build an image for a device.

I organized the compilation process into multiple stages for easier 
integration with our tooling. The last stage is a call to `wic` to 
create a drive image that we can then `dd` to a real drive to get a 
workable system.

I am faced with a problem where I would like the top-level directory of 
one of the partition created by wic to have a different owner than root.

I am able to tell wic the partition information (size, filesystem, etc.) 
but I can't find a way to tell wic to change permissions of 
files/directories inside the partition...

As an example I have an entry like the following at the end of my `.wks`:
 > part /opt/mnt        --label extra  --fstype=ext4 --align 1024 
--ondisk sda --size=2040
which will add an extra partition after all others on the final image. 
An entry in `/etc/fstab` will be added so that the partition will be 
mounted to `/opt/mnt`.

Note that the partition should be empty: I'm not populating it with any 
files or directories.

But after booting the system, the directory `/opt/mnt` will have the 
permissions of the top-level directory of the created partition, and by 
default those are `0755` and owned by `root:root`.

So my question is: How can I change this so that it's owned by a 
specific uid and gid (`1000:1000`)?

I am investigating plugins for now (for example by having a 
`meta-mylayer/scripts/lib/wic/plugins/source/fsimage-mypartition.py`) 
but I still can't see how I can change the owner of the directory. 
Should I provide a rootfs-like directory which is empty but owned by the 
proper uid and gid?

Note that letting users be able to mount the partition (by adding 
`users` to `/etc/fstab`) is not what I want; it would _not_ change the 
permissions/owner of the top-level directory of the partition.

Thank you very much!

Regards,

Nicolas